Imagine a room that is brightly lit but with no visible light fittings. Easy to do on a bright sunny day, but at night-time that is precisely what LED lighting can do – a real vision of the future. Although up to now a larger number of LEDs have had to be used to achieve the brightness levels of conventional light sources, their small size makes them extremely versatile and provides the impetus for new luminaire designs.
|OSTAR Lighting LED|
Even large LEDs are significantly smaller than fluorescent lamps or light bulbs. The Ostar from OSRAM Opto Semiconductors, for example, is hexagonal in shape and can be used to create either two-dimensional or three-dimensional arrangements. It produces lots of light (420 lm at 700 mA) in a very small space.
Powerful effects can also be achieved in furniture lighting. LEDs such as the 0.3 mm-high SmartLED or the slightly larger SideLED from OSRAM can be incorporated unobtrusively in furniture designs to produce small but impressive lighting effects. In such applications the LEDs themselves are no longer seen as light sources.
Excellent heat dissipation means that the LEDs are extremely safe. Their long life of up to 50,000 hours and therefore their low maintenance requirements enable LEDs to be fully integrated, and there is no need to make sure they can be easily accessed. Glass cabinets can be lit more effectively with LEDs than with fluorescent lamps. OSRAM MultiLED, for example, has three individually controllable colour chips in red, green and blue which can be mixed to produce any colour.
The right white for any situation
LEDs can do much more than provide light year after year after year while consuming very little electricity. They can create moods with crisp cool spotlighting or by simulating the cheering effect of natural sunlight – both are possible with modern converter technology.
The OSRAM Golden Dragon LED, for example, offers three different white tones with colour temperatures of 3250 K, 4200 K and 5600 K corresponding to warm white, neutral white and daylight white.
|Turning Torso tower|
This is a useful option not only for the domestic market but also for shop windows. During the day, the white light ensures that products appear in their natural colours. In the evening, coloured LEDs can create an eye-catching display all of their own. White LEDs such as the Golden Dragon or the Power TopLED from OSRAM can be mixed with coloured LEDs of the same type, which can be switched on and off as required.
Museums are another ideal application for light with different colour temperatures. Works of art can be highlighted without a spotlight to be seen. Thanks to the optimised heat dissipation of the SMT package there is no thermal stress on the illuminated objects, and sophisticated lighting solutions can be set up so that the lighting mood can be actively changed.
Use in outdoor lighting
As soon as the sun goes down, spotlights come on in every major city to bathe important buildings in light. Up to now this has involved high maintenance costs. The long life, low maintenance costs and low power consumption of LEDs make them particularly attractive not only indoors but also for outdoor applications. Compared with neon tubes they can save up to 80 percent of operating costs.
|Nutcracker at Boston Ballet|
It is not just on façades that LEDs can be used outdoors, they could revolutionise street lighting. Because LEDs are so small and weigh so little, the fittings do not have to be as bulky, either to accommodate the LEDs or to protect them from the weather. If equipped with a photo-voltaic system, LED path lighting need not be connected to an external power supply. This would also have an impact on operating costs. Again, the long life of LEDs would mean that there would be little or no need for maintenance work.
New technology for more light
Despite the many benefits, LEDs have only recently come into the reckoning for general lighting applications. For a long time, LEDs were not bright enough to warrant their use for room or façade lighting. A combination of new technologies has now overcome this weakness.
The process uses the substrate exclusively for growing the crystal and then it is removed. All that is left is a thin light-generating layer that is so close to the surface that almost all the light escapes at the top. With thin-film chips, numerous LEDs from OSRAM Opto Semiconductors have been given a huge boost in brightness. The Golden Dragon for example achieves a typical luminous efficacy of 40 lm/W in the cold white colour, 36 lm/W in neutral white and 32 lm/W in warm white, in each case with an operating current of 350 mA. This and the Ostar are two high-power LEDs that are now suitable for general lighting.
New technologies alone are not enough however to achieve maximum performance. The right combination is needed. Several chips connected in series ensure a much higher luminous efficacy. If a lens is then added to the LED, performance is improved still further. The best example is the Ostar Lighting high-power LED. This has six chips connected in series, producing a luminous flux of 300 lm. Combined with a suitable lens, peak output is boosted to 420 lm.
Producing coloured light the direct way
As in the case of conventional light sources, LEDs can bring colour to general lighting applications. The benefit of LEDs in this respect is well documented. They produce colour directly without having to filter them out of the visible spectrum. The result is much higher colour saturation than with other light sources, which in turn means more brilliant vibrant colours. Unsaturated colours, in other words white and mixed colours such as magenta and ice blue, can be created by a process known as luminescence conversion.
|Bostonian shoe store|
The light source of the future
In just a few years, LEDs have managed to gain a firm foothold in the general lighting market. Their enormous flexibility and impressive economy mean they can be used in an extremely wide range of areas and applications. What’s more, they are particularly kind to the environment. They contain no lead or mercury and comply with RoHS and WEEE directives.
New developments have not only closed the gap in brightness between LEDs and conventional light sources, they have given LEDs properties that surpass those of their rivals. However this is just the start for LEDs. Over the next few years they are expected to get better and better and better.