LEDs for general lighting

First, despite the marketing hype, technically there ain't no such thing as a "white" LED; typical contemporary (since the latter '90s), current-production commercial "white" LEDs in reality are Gallium Nitride-based (GaN) blue emitters (450-470 nm wavelength) the "lens" or package of which has been doped with a scintilator (sorta like a phosphor such as those which povide the luminance and chrominance of a CRT, but different), usually based on a combination of Cerium - Ce, Yttrium - Y, Aluminum - A, and Garnet - G, which upon excitation by the emmitter overlays the blue output with a broad spectrum bias centered on 580 nm (yellow), with variations of the composition of the doping resulting in shifts of apparent color temperature varying from warmish slightly yellow to cooler bluish (see: Variations of light characteristics of white LAEDs. Due to the way the human eye responds to the various wavelengths of light, the emmitted output appears to be white when viewed directly, however, the reflected illumination characteristics render red and green objects illuminated thereby noticeably, often objectionably, less vivid than is the case when such objects are illuminated by actual full spectrum white light (see: Raman Scattering. Earlier attempts at producing "white" LEDs involved the use of Near Ultraviolet emmitters, with other package doping, but were unsuccessful as the effect of ultraviolet radiation negatively impacts the transparent plastic package, or "lens" in which the actual LED semiconductor is embedded.

That said (and no doubt more than you wanted to know), while the illuminative efficiency of such emmitters individually is not high, ganging multiple emmitters, whether in the same package (again, the "package" is the transparent envelope or "lens" in which the actual light-emmitting semiconductor diode is embedded) or fabricating suitably configured arrays of emmitters does geometrically increase the effective light output. Current production Solid State Lighting Devices are of the latter type, arrays of many individual emmitters configured as a lamp assembly. Electrical efficiencies are on the order of around 30-35 lumens/watt, substantially greater than that afforded by incandescent illuminators which average from around 15-16 lumens/watt for conventional tungsten lamps to around 20 to 25 lumens/watt for halogen lamps, primarily due to the fact LEDs do not generate anywhere near the heat, or infrared, output per input watt as`compared to conventional incandescent illuminators.

While in terms of lumens-per-watt and lumens-per-unit-of-cost, florescent lighting still is far and away at the head of the pack, at least for today, ongoing LED illumination research and development promises near-term market feasability of substantially higher electrical efficiencies, though production considerations will allow both florescent and incandescent illuminators to enjoy considerable cost-per-lumen advantage for the foreseeable future.

The short version: "white light" LED illumination, presently at around 30 to 35 lumens-per-watt efficiency, is an emergent technology with great promise, though there are yet significant hurdles to be overcome before it achieves a cost-benefit advantage over conventional florescent and incandescent illumination in general lighting applications. That day certainly is coming, but it ain't quite here yet.

Thanks. Yes I know that LEDs are predominantly monochromatic by virtue of the way they generate visible light but in terms of general lighting, we are looking to improve and increase efficacy by decreasing heat losses in junction energy level transition AND increasing phosphor efficiency. I have heard of a company in the US called CREE that has set a rather impressive standard withing the last few months of approx. 130 lumens per watt but, of course, it is neither commercially available nor, when it is, will it be directly available for new luminary design by the general public.

Still, I think Solid State Illumination Technology is very, very close to exceeding some of the best fluorescent lighting systems currently available. I have some OSRAM High Output T5s running around 80 lumens per watt in my own workshop and they are quite extrodinary but I still look forward to Solid State Illumination just on general principles.

I agree there's major potential there. The future's gonna be different.



But then, it always is, isn't it?

Yes, it will be very different.

Now if we could just do the same with solid state heat pumps on a larger scale ...

Electroluminescent technology for general indoor light could easily beat out any further development of LED's in this application.

For instance, LED products in the retrofit PAR lamp and MR16 can only provide flood light configurations. Art galleries, for instance, rely on a variety of beam spread and expecially the very narrow spot (12 deg. typically). You need a single filament centered in the reflector and lense system to achieve that. Electroluminescence is already the wave of the future for Hi Def television displays and SONY already has introduced a 17" device (although very pricey). The techology has the potential to actually illuminate an entire ceiling or wall!