The aim of this paper is to examine future LED use in the commercial lighting market. Research was undertaken to identify the main factors that restrict the use of LEDs throughout the lighting industry. Insights will also be gained into potential uses of LEDs once their current issues have been resolved. This work fulfils the following objectives:

1. To gain an insight into the commercial lighting market, including:greater insight into commercial lighting applications and current technology used in commercial lighting.

2. To gain an insight into LED technology, including of past and current uses of LEDs in the commercial market and the advantages and disadvantages LEDs have over other lighting methods.

3. To gain an insight into how LEDs are and will be developing in the future, including areas LEDs need to develop in so that they can compete with other lighting methods and what effect this will have on future use in the commercial market.

In order to achieve the previously outlined objectives a number of key questions will need to be answered.

1. What types of commercial lighting are there that LEDs are currently used in?

2. What factors are there stopping LEDs from being used in a more widespread way throughout the commercial lighting market?

3. How can one expect LEDs to develop in the future, and what effect will this have on their use in the commercial lighting market?

This will show how current LED technology is being used and will give insights into specific features LED lighting and how these are being exploited in commercial applications and will highlight the downfalls of LED technology and the areas in which they need development. The focus is on how companies are developing LEDs to show where they see the short falls of LEDs lie which will give insights into where the market views LED technology is heading.

The following section will give an overview of the commercial lighting market. This will include looking briefly at types of commercial lighting and the technologies that are currently used in these areas. Research into this area has led to the main lighting manufacturers in the market, namely Philips lighting and Osram. Philips list the applications for commercial lighting to include office, retail, healthcare, hospitality, industry, urban, roads, sports, horticulture, habitat lighting, and petrol station lighting (Philips, n.d), the website for osram states similar areas. Philips also list commercial LED applications as being hospitality, offices, signage, retail and outdoor (Philips, n.d). Osram on the other hand sell LEDs under fewer categories. These being general lighting, decorative lighting and signage (Osram, n.d). The fact that these two main suppliers of LEDs seem to differ in their opinion of how LEDs can be used gives a good indication of how the LED market is at the minute. LEDs are rapidly developing and as such their current use does not necessarily reflect what they will be used for in the future. For the purpose of this work commercial lighting will be classified into the following categories:

• Office Lighting – this will include general-purpose lighting of office spaces and buildings.
• Display Lighting – this concerns applications such as retail and other types of display including art exhibitions and display stands.
• Exterior Flood Lighting – this will look at types of exterior lighting where large areas are lit including sports areas and road lighting.
• Exterior Decorative Lighting - this area focuses on types of lighting where the level of illumination is not necessarily the most important factor. This type of application will focus on the decorative lighting of buildings and other structures, for example the O₂ centre (formerly the millennium dome).

Table 1 below shows the various forms of commercial lighting that will be looked at with reference to the use of LED technology. The table highlights the current technology that is widely used and the features that a light source requires to be suitable for use in that application. These criteria will be compared with the characteristics and limitations that LEDs have in order to gain insights into what applications LEDs are likely to be used for in the future.

Table 1. Commercial lighting applications and their requirements

The following section will look at the available literature on the subject of LED lighting. This will be used to ascertain what the restrictions are that need development to allow for widespread use of LEDs in the commercial lighting market.

2.1. Past uses of LEDs

“LEDs have gained broad recognition as the ubiquitous little lights that tell us our monitors are on, the phone is off the hook or the oven is hot.” (Steigerwald, et al., 2002)

When most people think of LEDs the above often outlines what many people would think of first. The first LEDs to be commercially available were red and had luminous efficacies of 0.15 lumens per watt (lm/W) (Steranka, et al., 2002). With light outputs as low as this the only use they could have was as indicator LEDs. Developments in 1994 by Hewlett Packard saw LEDs developed at 25lm/W; however, with only 3 lumens per LED they were still confined to “those applications where the user was expected to look directly at the LED” (Steigerwald, et al., 2002) . Although this lack of brightness did stop them from being used for general lighting applications, the rise in luminous output did open up new areas of use. Indeed this rise in luminous output “enabled the first LED stop lights in automobiles, LED red traffic signals and single colour outdoor signs” (Steigerwald, et al., 2002) . Overall, past LED use was dominated by the indicator market, with little to no use found in the lighting sector.

2.2. Current uses of LEDs

When looking at what applications use the greatest number of LEDs there is one area that still vastly outweighs all the others. “In terms of number of LEDs sold, indicators and other small signal applications in 2002 still consume the largest volume of LEDs, with annual global consumption exceeding several LEDs per person on the planet” (Steigerwald, et al., 2002) . This may come as no surprise; it is hard to find an electronic product that does not include the use of an indicator LED somewhere on it. It is recent developments in high power LEDs that have bought about their use in lighting applications.

LED usage in the current commercial lighting market is heavily biased towards one area, this being exterior decorative lighting. As previously stated, lighting here requires light sources that can supply various colours, direct the light to a specified point and also to be able to emit a large amount of light. Previous forms of LED could not compete with other sources of light due to their lower light output. However “demand for LEDs is strong in architectural lighting applications” (Mintel, 2008) “as a results of associated product advantages including a long life span and high energy efficiency” (Mintel, 2008). The view of these advantages is something that is shared by many; “maintenance and excellent visibility are the main drivers for using LEDs in this application” (Arik, et al., 2002).

As well as being decorative, display lighting is another area where LEDs are starting to be the preferred light source. This can include anything from displaying artwork in a museum to highlighting clothes in a high street shop. Whatever the application the reason for choosing LEDs is often the same. Their small size allows for them to be discreetly built into the scene they are displaying. Their long life allows for low maintenance reducing costs to the user. Costs are further reduced by LEDs high luminous efficacies. Another key point for many display applications is that the LEDs do not throw any heat onto the item they are illuminating, a key point for displaying food and other perishable or delicate items.

2.2.1. The O₂ Centre – Exterior Decorative Lighting

In 2007 Philips lighting were “charged with creating a striking visual design made up of a combination of floodlighting and LEDs” (LEDs magazine, 2007b) for the O₂ Centre (formerly the millennium dome). This example of display lighting is a good illustration of a large-scale project that would see “1.8 million LEDs installed around the exterior” (LEDs magazine, 2007b)

Each of the 12 yellow masts emerging from the top of the dome now encorporate 6 philips blue BendiLED hoops used to represent the O₂ bubbles. These BendiLED hoops have also been used to highlight each of the 12 LED displays screens around the perimeter of the dome. Figures 1 and 2 show the O₂ centre after the LEDs have been installed.

Figure 1. The O2 Centre lit using Philips LEDs

Figure 2. LED display screens

Figure 3. Victoria Square glass dome lit using Philips LEDs

Figure 4. Conventional Painting Display lighting compared with LED alternative

Figure 5. Large image lit using MU.SE, top right using traditional lighting, bottom right with a yellow light spectrum

As can been seen from Figure 5 the BendiLED hoops on the 12 masts are installed in hard to reach areas. One advantage of LEDs, their long life span, has made them good candidates for exactly this sort of application. Having to replace a broken lamp in these fittings would be a high cost job and so anything that can reduce how often this needs to be carried out will be of benefit to the user. Lights such as the Cosmo White shown in Figure 4 have a burn time of around 30,000 hours. Manufacturers of LED technology claim burn times of anything from 50,000 to 100,000 hours. If these figures are true the use of LEDs could mean that time between maintenance could be doubled or even tripled. How reliable data from manufacturers actually is, is something that many are unsure of. This will be looked at in more detail in a later section. However, within the current market it seems as though the products are living up to people's expectations with more companies using LEDs for these applications.

2.2.2. Victoria Square, Belfast – Exterior Decorative Lighting

Another example of decorative lighting using LEDs can be found at the Victoria shopping centre in Belfast, shown in Figure 3.

Again carried out by Philips lighting, 400 of their iColor® MR g2 fixtures were fitted to the glazing intersections. The choice to use LEDs was made for a number of reasons.

“Aesthetically they can generate millions of colours and dynamic effects without gels, filters of mechanical scrollers. Moreover, operationally they require very little maintenance and produce little to no radiated heat.” (Philips, n.d).

Here, much like with the O₂ centre, it can be seen that the extended life of LEDs and the benefits this brings to maintenance needs, was a big factor in choosing LEDs over other light sources. Moreover, in this case the ease with which they can create different colours and effects without changing the fittings was beneficial. The system that has been installed is said to be “capable of playing a large quantity of light show effects” (Philips, n.d). This is all controlled via an ethernet based remote control and so the user can create the effect they want from ground level without even touching any of the fittings. It is this high level of adaptability that has helped make LEDs popular for decorative lighting.

2.2.3. Osram MU.SE – Display Lighting

A good example of LEDs being used for display lighting is their use in the Osram MU.SE (short for museum selection) project luminaire. Developed for the Bellini exhibition in Rome the MU.SE uses LEDs as they are “small and durable, require little maintenance, consume very little power and emit no heat onto the exhibit” (Osram, 2008). This last point is important due to not wanting to damage the painting in any way. Another important factor in protecting the painting is “that an excessive proportion of infrared waves and UV emissions will cause colours to fade and damage the surface of paintings” (Osram, 2008). The risk of heat from infrared waves and damaging UV emissions does not exist when lighting with LEDs. This allows for the LEDs to be placed near to the paintings instead of projecting their light from across the room. Figure 4 shows how the LED system can be used in comparison to conventional lighting solutions.

As can be seen with the LED system the lights can be much closer to the painting without damaging it, making the display more compact. As well as being less damaging to the paintings LEDs also have benefits in energy consumption. The MU.SE LED system “consumes only 3,330 kWh over 25 years at 4,000 hours of operation a year compared with 13,500 kWh for conventional light sources” (Osram, 2008). These sort of energy saving correspond to about 5 tons of CO₂.

Alongside saving money through the energy efficiency, users can also save money because of the LEDs long lifetime. “Where as conventional systems needs to be maintained every six months, the MU.SE can run for 12.5 years without an inspection,” (Osram, 2008). Above all of these benefits the light produced by the LEDs in MU.SE is set up to show the paintings off the best way possible. Figure 5 compares the effect achieved when a painting is lit using the MU.SE LED system compared with other conventional lighting systems.

Using the LED system the painting is lit so that the colours are represented, as they should be. “LED luminaires provide the “purest” form of white light. There are no disturbing deviations in the light and the light can be finely controlled” (Osram, 2008). It is this fine control over the light that means the best lighting effect for each display can be achieved with the lighting system effectively being tuned to each setting's requirements. This tuneable nature of LEDs, and the ease at which it can be done is a feature that sets them apart from many other types of light source available.

2.3.Developments in LED Technology

As has been seen in the previous examples there are areas where LEDs have made a significant impact on the commercial lighting market. However, there are still a number of areas where companies would like to employ the use of LEDs but the technology currently available is not sufficient to fulfil their requirements. This section will look at how the technology is developing so that LEDs can be used in more commercial applications.

2.3.1. Luminous Output and Efficacy

Unsurprisingly one of the main areas in which companies are trying to develop LEDs is in the amount of light that is emitted from a single chip and also the amount of light that can be emitted for the least amount of energy consumption. As previously stated the first LEDs developed were only capable of producing small light outputs. “Developments in the 1980s and 1990s led to the introduction of high brightness LEDs, where the devices produced enough light to provide illumination, although initially at very low levels” (Arik, et al., 2002). Indeed it is true that these developments in high brightness or high power LEDs have continued up until the present day and will continue until LEDs have reached the sort of light outputs and efficacies that are promised. This focus on the development of light output reflects the view that as the luminous output of LEDs increases the number of applications that they can be used for will also increase.

Figure 6 shows the graph (Arik, et al., 2002). used to demonstrate how they view LED usage will change as the luminous output increases. This shows that for LEDs to be used in general lighting applications they need to have a luminous output of over 100 lumens. In order to compete with other light sources with respect to luminous efficacy, LEDs will need to produce over 100 lumens per watt of energy consumed. Tubular fluorescents have efficacies of 60 – 110 lm/W and compact fluorescents have efficacies of 50 – 70 lm/W(Boyce, 2003).

Figure 6. Application Opportunities for LEDs based on Light Output Arik et al, 2002

If LEDs are to replace these in general lighting applications it is the luminous efficacy that will need development. It can be assumed that this is what companies will look to do, as “general illumination is the ultimate vision for LEDs” (Arik, et al., 2002). Steigerwald, et al (2002) speak of how for the past 30+ years LED luminous output has been following what is know as Haitz's law. This predicted that the luminous output of LEDs would double every 18-24 months. Figure 7 shows how the luminous output of LEDs has developed over the past 30+ years (note the increase in light output per LED package).

Figure 7. Haitz's Law for LED output – Luminous output has doubled every 18 -24 months for the past 30+ years (Steigerwald et al., 2002)

Although it is important that this continues to happen this may be down to the chips themselves just getting smaller and so more chips can be put into a light fitting or lamp and so the light output will go up. The figure that is most important to the industry at the minute is the luminous efficacy or lm/W. This is the figure that shows how much light is produced for every watt of energy consumed. The higher this is the less energy the user will have to pay to run the light compared with a light source with a lower luminous efficacy Steranka, et al (2002) . write of how over the past 40 years the luminous efficacy of LEDs has been increasing by a factor of roughly 10 per decade. The increases made can be seen in Figure 8.

Figure 8. Improvements in LED luminous efficacy over the last 40 years Steranka, et al (2002)

The main points of interest of this graph are the position of the best LED devices compared to the fluorescent lamps. When comparing these it can be seen that by the late 90s various colours of LED were approaching similar efficacies as fluorescent lamps. At the date this graph was produced however, white LEDs were still a fair way behind. Since then white LEDs have come a long way and are now competing with the fluorescent lamps. Recent papers state “Osram is claiming a record for luminous flux and efficacy from an LED driven at 350mA” (LEDs magazine, 2008d). Here they claim to have developed a white LED that emits 136 lm/W when driven at 350mA. Compared to fluorescent tubes with efficacies of up to 110 lm/W, LEDs with these sorts of efficacies pose energy saving potential.

The main way that LEDs have developed to improve their efficacy is in the way that white light is produced. This is done in a number of different ways. One method is to have red green and blue LEDs all on one chip. When the correct levels of the three colours are mixed white light is produced. This colour mixing approach is often know as RGB and is the most efficient way of producing white light from LEDs. However, this is less popular than the main other method due to having to use more than one LED. As the LEDs age at different rates the mix of colour can change and so the quality of white light will deteriorate. “In more sophisticated versions, onboard electronics adjust the individual drive currents to change the correlated colour temperature” (Steigerwald, et al., 2002). This method helps to solve the issues with colour mixing but requires constant feedback and complex electronics all of which raise the cost to produce consistent white light.

“By far the most common LED-based white light source is the phosphor coated LED (pc-LED)” (Steigerwald, et al., 2002). This uses a blue LED coated in a complimentary yellow phosphor. As the blue light from the LED shines through the phosphor white light is emitted. Developments in the phosphors used have accounted for the major advances in the luminous efficacy of white LEDs. For the 136 lm/W LED previously mentioned Osram say “the key to success was a perfectly matched system of optimised chip technology, a highly advanced and extremely efficient light converter (phosphor) and a special high-performance package” (LEDs magazine, 2008d). The keyword here is efficient. As the phosphor technology has become more efficient the amount of light lost in converting the blue light from the LED to white light has been reduced. Consequently, the overall efficiency and efficacy of the LEDs have also increased.

2.4.100 Champs-Elysées – General Lighting

To show how their LEDs are developing, companies often set up projects where they use their latest developments in a new way. One example of this is the offices at 100 Champs-Elysées. Here Philips lighting have lit the entire office building using only LEDs in the hope to achieve “both functional and decorative lighting” (LEDs magazine, 2008b)

Figure 9 shows the LED luminaires that have been used. The fittings each contain 16 or 12 high power (2.6w) LEDs depending on their position in the office. These are installed into the suspended ceiling to provide “an average of 300 lux everywhere and 500 lux on the working planes” (LEDs magazine, 2008b).

Figure 9. Office lit entirely with LEDs

Projects like this act as “a moment of truth and are proof that LEDs are making inroads into the heart of the lighting industry” (LEDs magazine, 2008b). Being able to light an office with only LEDs to the required light levels does indeed prove that the technology is capable of being used in this way. The job now is to be able to make the technology live up to all its hype in terms of energy saving. This will make people actually want to use LEDs instead of more proven light sources, such as fluorescent tubes.

2.5. North Dumpling Island – General and Decorative Lighting

Another project, again undertaken by Philips, has this time seen not only a whole building but a whole island lit using only LEDs. North Dumpling Island is 3 acres in size and is owned by Dean Kamen. It was after the US coast guard cut the electrical power to the lighthouse on the island in favour of solar power that Dean “decided to convert the island to LEDs”(LEDs magazine, 2008c). Figure 10 shows a few examples of how LEDs have been used on the island to create both functional and decorative lighting effects.

Figure 10. North Dumpling Island LED usages

The conversion means that the island achieves a “net zero energy, meaning its energy use will be negated by its energy generation” (LEDs magazine, 2008c). This has been made possible firstly by switching to solar power but also by large energy savings through the switch to LED lighting. Savings have been made through replacement of the incandescent sources within the properties “cutting their lighting related energy by 70%” (LEDs magazine, 2008c). It is not only the efficiency of LEDs that has helped to save energy on the island. With the decorative floodlighting “improvement in the “usefulness” of illumination via the directional nature of LED sources, which, unlike the island's former floodlighting system, project their light exactly where it is needed for greater efficiency” (LEDs magazine, 2008c).

Much like with lighting an entire office, the cost of the LEDs compared to other light sources would be much greater. However when speaking about the island Kamen said “with increasing strain on our world's energy resources, our goal is to make North Dumpling a small but prominent example of what can be achieved on a larger scale with today's emerging energy saving technologies.” (LEDs magazine, 2008c). With energy saving of this scale achievable with the technology already available it can be seen that with further development in terms of function and efficiency LEDs will become an ever increasingly attractive form of lighting. This will be especially true for energy efficiency. Rising government interest in energy saving now means that by 2011 all sales of inefficient GLS A-shaped lamps, everyday lamps used in light fittings all over the country, will cease. It is believed that this will “lead to increase sales of compact fluorescents and LEDs” (Mintel, 2008)

2.6. Organic LEDs (OLEDs)

Up until this point, the focus of this paper has been on inorganic LEDs. However, there is another area that is quickly developing and is hotly tipped to be the “next light source to gain widespread use, after light bulbs, fluorescent lamps, and compact fluorescent lamps.” (Karpuik, 2006). This opinion of OLEDs seems to be one held across the industry, “OLEDs are projected to become the main type of room lighting in the medium to longer term” (Mintel, 2008). Exactly how long it will take for OLEDs to become this widespread is not clear and depends on how quickly they can be developed. Figure 11 shows an example of what an OLED looks like.

Visually the main difference between an LED and an OLED is that an LED is a point source of light and an OLED is an area source. It is this ability to have large areas of emitting material that is perceived to be one of the OLEDs main advantages. This feature along with others has led many to believe that as the OLED develops it “will open up entirely new applications.” (Mintel, 2008) Along with being an area source, the type of areas that they will be able to be applied to is also of interest. OLEDs will be “capable of being used in a variety of different ways as flat, transparent and, in the future also, flexible sources of light.” (LEDs magazine, 2008a). These features do indeed open up a new host of applications not currently achievable with current light sources. For example a flexible OLED could be made into a curtain that can be used as a normal during the day, put away when light is not needed. When it gets dark the curtain is drawn and can be used to light the room. Alternatively, a transparent OLED could be used as a window, once again meaning that during the day it would let light from outside through and when it gets dark it can emit its own light and illuminate the room. “Almost any surface, whether flat or curved, could become a light source: walls, curtains, ceilings, cabinets or tables. Since OLEDs are transparent when turned off, the devices could even be installed as windows or skylights to mimic the feel of natural light after dark.” (Gizmag, 2006).

Much like with inorganic LEDs, OLED technology is being developed so that it is bigger and brighter to enable use in a wider range of applications. These developments, although happening quickly, are still behind inorganic LED technology. BASF and Osram have recently made claims of developing a white OLED capable of 60 lm/W, about which the two companies say they “have completed a major step towards commercial OLED lighting” (LEDs magazine, 2008a).

The widespread interest in OLEDs and in particular the development of this technology has led to a number of different projects being set up. Each of these projects sets a number of goals that want to be achieved and also a time scale in which they are to be done. An example is the OLLA project (Organic Light Emitting Diodes for ICT & Lighting Applications). The aims of this were to develop an OLED with an “efficacy of 50 lm/W, lifetime of 10,000 hours from an initial brightness of 1000 cd/m, with a tile size of 15x15 cm” (OLLA project, 2008). A group of 24 companies were involved from 8 different European countries and aimed to achieve these goals over a 45-month period. Similar projects such as the Next-Generation-Lighting Initiative in the United States and the Lighting 21 program in Japan are happening all over the world.

By the time of its conclusion on 1st July 2008, the OLLA project had successfully met its targets by developing an OLED with “an efficacy of 50.7 lm/W at an initial brightness of 1000cd/m” (OLLA project, 2008). This work is seen throughout the lighting industry as “laying the groundwork for transforming OLEDs into a commercially viable technology.” (Karpuik, 2006). The number of projects, companies and countries involved in the development of the OLED gives a good indication of how important this technology is deemed to be. Already started on the 1st September 2008, just two months after the OLLA projects conclusion, a number of the companies involved in the OLLA project are now working on the OLED 100 project. This is set to run for 36 months and has the following targets:

• High power efficacy – 100 lm/W
• Long lifetime – 100,000 hours
• Large area – 100 x 100 cm
• Low Cost – 100€ /m
• System Integration / standardisation / application

These targets have been set to enable the OLEDs to be able to compete with the leading equipment in both “existing and upcoming lighting solutions” (OLED 100, 2008). This includes “efficacies of up to 100 lm/W (fluorescent tubes) and lifetimes of up to 100,000 hours (inorganic LEDs)” (OLED 100, 2008). The project is due to end on the 31 August 2011 and so it is likely that OLED technology will not be able to compete with other lighting types on a commercial scale until a number of years after this date. Success, however, will prove OLEDs can compete with the best lighting technology available. This will put them in a good position to “become the main type of room light” (Mintel, 2008).

Although the aim of OLED 100 is to put the OLED in a position where it can compete with the inorganic LED, it is believed by some that “the two technologies should be regarded as complementary rather than having an effect on each other” (Nathan, et al., 2007). This view is held due to the point and area source differences in the technologies. This difference in how the two types of LEDs emit their light is believed by some to mean that they will both be suitable for different applications. This theory falls down where both types of LED aim to be used for the purpose of general illumination. Various companies have made estimations about both types of LED stating, “OLEDs are projected to become the main type of room lighting” (Mintel, 2008). and that “general illumination is the ultimate vision for LEDs” (Arik, et al., 2002). (Arik, et al., 2002). As to which type will eventually win out as the dominant lighting source for general illumination, it can be assumed that it will be the source with the best efficacies and lowest cost.

Every effort has been made to get the most up to date information available, with the majority of sources being published in the last few years. However, the speed at which the LED market is developing can mean that information published only a matter of months ago may already be superseded by new technological advances. To overcome this the next section will look at interviews held with professionals who work in the area of commercial LED lighting. These people will not only have the most up to date knowledge that cannot be found in books or journals, but will also have first hand experience in using the technology. This will be useful in giving insights into how LEDs actually measure up in practice compared to the technical data that companies release about them.

3.1 Constraints of Interviews

Although interviews will give the most up to date information they do have their limitations. The main issue with gathering data in this way will be the number of people able to be interviewed. The time it takes to organise an interview and also the unwillingness of some people to be interviewed will limit the results gathered. This will mean that the opinions expressed may not totally represent the whole market. As with any sort of survey the more participants that take part the more reliable any trends that emerge will be. With this in mind it will be issues that more than one person raises that will be of most importance and can be regarded as to represent the views of the commercial lighting market.

The importance of eliminating “cues which lead the interviewees to respond in a particular way” (Robson, 1996) cannot be underestimated. It can easily happen that “interviewees seek to please the interviewer by giving the 'correct' responses.” (Robson, 1996). It is therefore important that leading questions are avoided in order not to distort any data gathered. The interviews carried out will be semi structured in that there will be a number of topics that will be discussed but the exact questions to be asked will not be decided until the interview has begun. “Face to face interviews offer the possibility of modifying one's line of enquiry, following up interesting responses and investigating underlying motives in a way that postal or other self-administered questionnaires cannot” (Robson, 1996). This is the exact reason for choosing a semi structured interview over a questionnaire. As the interview develops further topics will arise and from this a greater insight into the commercial LED market will be aquired.

Interviews also offer benefits in the standard of information that can be gathered as “the interviewer is in a good position to be able to judge the quality of the responses” (Walliman, 2005). The interviewer can read body language and facial expressions to ensure the question has been fully understood. This is something that can not be judged easily when using questionnaires or other research methods where the researcher is not present when the questions are answered. Non-verbal cues can also be used to help understand the meaning of a response given “possibly changing or even, in extreme cases, reversing its meaning” (Robson, 1996).

3.2.Interview Structure

Although the interviews will remain open to change as they happen there will be a number of topics that will be covered as a minimum. (Robson, 1996). compares a semistructured interview to a shopping list of topics requiring responses where considerable freedom in the sequencing of the questions is given to the interviewer. The areas to be covered in each interview will be as follows:

• In what areas does the interviewee's company currently use LED technology?
• What short falls does the interviewee see in current LED technology that are stopping them being used in other applications?
• How do they see LED technology developing in the future and what areas will it be used in?

These topics will be expanded on significantly to gain useful and insightful responses from each interviewee. Interviews were held with the managing director of Projection Lighting, and the technical services manager at Osram (UK) Ltd.

3.2.1. Areas of Current LED Usage

Unsurprisingly when talking to technical services manager of Osram, the list of areas in which they already sell LEDs is much the same as can be found on their website. “Discreet LED components direct into the electronics industry, automotive, general lighting, display lighting, accent lighting, LED luminaires – most are already covered” (Ford, 2009). Projection Lighting on the other hand seem to have focused on the “interior lighting and down lighting,” area of general lighting. This would fall under Osram's general lighting, “we do have some LEDs that are now just starting to be used for general lighting but mainly as low wattage equivalents – e.g. LED equivalent of a 20w spot lamp” (Ford, 2009). Whatever areas are sold into it is evident that in each company LEDs are not the major light source for commercial lighting applications. The reasons for this will be looked at in the next section.

3.2.2. Current Issues with LED Technology

As has already been identified from literature available, the main area in which LEDs have and need to develop is their total light output and luminous efficacy. This is something that is backed up by both interviewees, the main areas that need development are said to be “the total light output capability of the LEDs and some efficiency improvements” (Ford, 2009). managing director of Projection Lighting sees development needed in both luminous efficacy and also the quality and “colour of the light output” (Heald, 2009). Despite companies quoting luminous efficacies of around 100 lm/W it is often the case that these figure are not actually achievable in practice. “The manufacturers state the best outputs they have achieved in lab tests” (Heald, 2009) in truth, however, these figures are never going to be achieved in real life, “the best you're going to get out of an LED is 70 lm/W. That's once it's in a fitting and in situ” (Heald, 2009). With these figures it can be seen that to compete with fluorescent lamps, with efficacies of up to 110 lm/W, a certain amount of development is needed in this area.

The quality of light emitted needs to be looked at in conjunction with another issue of current LED technology, their overall cost. The quality of the most expensive LEDs made by the main manufacturers is of a good standard, the issue arises when users by cheap LED fittings. “Here every thing is price driven”, “they see poorly made fittings that give out harsh blue light and they get put off” (Heald, 2009). All across the commercial lighting market in this country, not just with LEDs, cost is the main driving factor. It is therefore the case that the high quality needs to be achieved for a lower cost. “In the short to medium term LEDs will be able to replace fluorescent from a technical point of view (light output – if you have enough of them/efficiency and life) but they will be many times more expensive for the same application – maybe up to 100x more 'per meter' currently” (Ford, 2009).

In many ways the above statements can be applied to both inorganic LEDs and OLEDs. It is true to say though that, “OLED technology is some way behind in both efficiency and output” (Ford, 2009). This has a great deal to do with the relative ages of both types of LED, with OLEDs being a much younger technology and as such are not as far developed.

3.2.3. Future Developments and Uses of LED Technology

As previously highlighted, it is viewed that the main short falls of LED technology are in luminous efficacy/output and cost. Unsurprisingly it is also believed that these are the main two areas in which LEDs will develop in the coming years. Ford (2009) states, “LED efficiency and light output are expected to keep increasing rapidly in the next few years”. Gary Heald (2009) goes further to map out a projected time line for the development of LEDs luminous efficacy, “currently available LEDs can have 100 lm/W. In a years time this will be 120 lm/W and the year after that 140 lm/W”. This sort of estimate of LED efficacy exceeding that of fluorescent lamps “in the short to medium” (Ford, 2009) is held across the lighting market. It is estimated that LEDs “have the potential to reach 250 lm/W” (Heald, 2009) this is something that is backed up by the literature available where LEDs have been tested that give off “300 lumens of visible light for every watt of energy” New Scientist. 2008

During the review of the literature it has also been made apparent that developments in phosphors have been key to the development of luminous efficacies/output in LEDs. The interview with managing director of Projection Lighting further backs this up. (Heald, 2009) talks of remote phosphors and tuneable LED systems and how they will be the “backbone of LED development”. These systems allow for fine control over the quality of light emitted from the LED and, through the development of new phosphors, also increase the efficiency of the LEDs. This all works together to improve the quality and overall usefulness of the LEDs.

The quality of light emitted is only really an issue for interior use of LEDs. When it comes to exterior lighting, especially flood lighting, users are not especially worried about the colour of light. “Quality of light in exterior applications is not regarded as important. We have only just moved away from using SOX lamps for streetlights etc. The lights that give an orange tint to everything” (Heald, 2009) Because of this is can be seen that for LEDs to be used more in exterior flood lighting “it's only really the luminous efficacy of LEDs that needs to be improved” (Heald, 2009)

The cost of LEDs is not something that can be lowered easily or quickly. This is something that will happen over time, “as more LEDs are used costs will come down” (Ford, 2009). This of course is true of any new technology. It is also viewed that the price will fall due to the wide range of areas that LEDs are being developed for outside of the lighting market, for example “LCD flat panel TVs use LED backlights” (Heald, 2009) and “the motor industry” (Heald, 2009) is another large developer of LEDs. The more widespread the use of LEDs is the quicker their price will fall.

As already seen LED technology has developed a long way since its creation in 1962. However, if a more widespread use throughout the commercial lighting market is to be adopted further development in a number of areas is still required. This section will identify what these areas are and how LEDs need to develop to overcome the issues.

4.1. Luminous Efficacy

Throughout much of this paper the issue of luminous efficacy has come up repeatedly. This is important for two reasons. The first is to do with there being more applications LEDs can be used for if their light output is higher, as illustrated in figure 10. The second reason is to do with the growing government and public interest in energy saving, “energy efficiency is increasingly important reflecting rises in energy costs, along with increased awareness in energy conservation and legislation aiming to reduce carbon emissions” (Mintel 2008). As the luminous efficacy of LEDs rises so too will their energy saving potential, thus making them an attractive source of light for people wanting to save energy.

At the moment manufacturers quote the best LEDs to have efficacies of around 100 lm/W, around the same as fluorescent tubes. These figures are achieved in laboratory conditions and as such the end user will not get the same performance once the LED is installed, “the best you're going to get out of an LED is 70 lm/W” (Heald, 2009). Because of this LEDs are not yet an improvement in energy efficiency over the more established fluorescent tubes. It is, however, clear that LEDs are heading in the right direction and as long as they keep developing as they are, they will one day supersede other lighting technologies. Figure 12 shows how LEDs and fluorescent tubes develop from when they are first invented to when they reach “maturity”, that is they are developed to a point where the maximum output is gained from the technology .

Figure 12 shows how the life of the technology can be broken down into two stages. The first “development” is where LED technology currently is. As has been shown throughout this paper LEDs are improving on an almost daily basis. They are starting to compete with the luminous efficacies of fluorescent lamps and are set to surpass them soon. The second stage is where fluorescent lamps have reached. Development of fluorescent lamps has come to a near stand still with their luminous efficacy seeming to have reached a maximum. LEDs are a way off reaching this stage and so it will be the development from where the technology is now that will see them achieve luminous efficacies greater than fluorescent lamps. “The best way of putting it is that LEDs are just coming of age” (Heald, 2009)

Figure 11. A white lab scale OLED Prototype measuring 7x7 cm

Figure 12. Development stages of LED and fluorescent lamps

4.2. Cost

The second main stumbling point for LEDs presently is their overall cost. Exactly how too much they are is not clear and depending on whom you talk too different opinions are expressed. “A typical incandescent bulb produces approximately 600 lumens and retails for less than $1. A similar amount of light output from LEDs would cost about $60 based on current LED lamp pricing” (Arik, et al., 2002), this was in 2002. However, even in 2009 people hold the view that LEDs are ”many more times more expensive for the same application – maybe 100x more 'per meter' currently” (Ford, 2009). Where ever you look though it is clear that “the short term growth in this sector is likely to be constrained by price, as LEDs are believed to be around 20 to 30 times more expensive than filament lamps and 10 to 15 times more expensive than CFL and other fluorescent lamps” (Mintel, 2008).When talking about cost it is necessary to take into account more than just the upfront cost, “LED costs must count things far outside of just the fitting. Their longevity and energy saving costs all count” (Heald, 2009). Fluorescent lamps can be expected to last for 20,000 hours where as LED lamps can last for anything from 50,000 up to 100,000 hours. This would mean that LED technology would last for 2 to 5 times longer than fluorescent technology. With this and the energy saving potential that LEDs have, it can be assumed that LEDs are likely to cost more to buy than other light sources. Even considering this, LEDs are still too expensive to be a viable alternative for many applications, “ People currently installing them are doing so on a cost vs. benefit basis considering some of the unique features of LEDs” (Ford, 2009). A good example of this is where LEDs have taken off in exterior decorative lighting where the benefits of long life and adjustability outweigh the added cost of using LEDs.

4.3. Availability

One issue LEDs would have if they were to be used in a large scale currently would be the quantity they are available in. “Within three years the technology will have surpassed the fluorescent tubes but won't be available in quantities to replace the tubes totally” (Heald, 2009). This will of course be something that would change once the demand for LEDs gets larger. Much like with cost until there is the demand for large number of LEDs their availability in large quantities will not change.

LED technology has developed to a point where there are a number of areas that it can be used in successfully. The main area is exterior decorative lighting, here the LEDs long life and high levels of adjustability of light colour and brightness make them useful despite still being expensive compared to other light sources. Another current use is that of display lighting. Here the fact that LEDs are small and do not project any heat or UV rays onto the item they are lighting is advantageous. This is especially true where the items to be lit are delicate such as paintings or food.

The main area of future LED development is in luminous efficacy. Currently LEDs have luminous efficacies on par or slightly lower than fluorescent lamps. These are the main rivals to LEDs being used in the application of general illumination. It is the belief that the phosphor coatings of LEDs will, in the short to medium term, develop so that LEDs technology will surpass fluorescent tubes facilitating better energy saving opportunities. “LEDs have the potential to reach 250 lumens per watt” (Heald, 2009). Also as the luminous efficacies and output of LEDs increases they will be able to be used for flood lighting. It is likely that they will feature in this application before general illumination, as the quality of light is not as important for flood lighting.

Development of OLEDs will see transparent and flexible version become available. Because of this they will be able to be used in innovative ways not seen before. This fits in with the views that LEDs and OLEDs “should be regarded as complementary rather than having an effect on each other” (Nathan, et al., 2007). Table 2 and 3 show 4 commercial lighting areas identified earlier and summarises where LEDs need to develop to be suitable for each application.

Table 2. Areas for LED development in commercial applications

Table 3. How LED developments will affect use in commercial applications

Table 2 shows that in many areas the restricting factors are the luminous efficacy followed by the cost. The LED market is developing at a fast pace with the aim of becoming an alternative to other sources of lighting.

Predicting the future can obviously never be 100% certain, but it is definitely the view of the industry that LEDs and OLEDs will play a key part in energy saving lighting in years to come, “LEDs are expected to represent at least one third of the general lighting market by 2020” (Mintel, 2008). The speed at which this actually happens depends highly on how quickly the high quality LEDs produced in labs with high luminous efficacies, become commercially available at a reasonable price.

The focus of further research could be on LED cost. The commercial market is highly driven by cost and as such research into the projected costs would be both interesting and valuable with respect to LED use. Within this research areas such as the current cost, projected future cost and time scales should be looked at. This would give a clearer view of when LED technology is likely to be able to compete on a cost level in the commercial market.