06-Nov-02: We continue to receive enquiries about using LEDs for room lighting, street lighting, car headlamps, and so on. The bottom line is this: white LEDs are about the same efficiency as tungsten halogen lamps, but use only 70mW of electrical power. Simple mathematics tells you that if you want the equivalent of a 70W lamp you will need to use a thousand LEDs! No doubt LEDs will rise in efficiency, but it will be hard to beat the efficiency of gas discharge lamps (e.g. fluorescent lamps, sodium lamps for street-lighting). Before you ask us about this type of project, please read our previous replies on the subject, as reproduced below.
>Read your article on making cave lamps using LEDs. I am about to refurbish >an office area (approx 700') and have thought of replacing the old lighting >by flooding the ceiling with LED's. Any ideas or thoughts you may have >would be appreciated. Too expensive! LEDs will rival conventional lighting one day, but they just arent bright enough at the moment. A fairly dim LED torch might use 12-20 LEDs. Now think how many torches you need to light a room to 'daylight' levels. Or - to give you a calculation - LEDs are currently about the same efficiency as halogen lamps (which is about a fifth that of fluorescent lamps). Each LED is about 70 milliwatts. If youve got ten x 80W strip lights that's 800W, so you need five times as many LEDs, that's 4000W-worth. At 70mW each, that's almost 60 thousand. And at, perhaps 50p each ... that's a lot of money. It would look nice though.
> I have some questions about the use of LED lighting as street > lights. > 1. Is it possible today to develop enough light from LED to be used > for street lighting? No. High-pressure sodium lamps have an efficiency of at least 86 lm/W, which is over five times that of a white LED. monochromatic yellow LEDs are bit better, so lets be optimistic and say four times. so you would need to replace a standard 70W sodium lamp with 280W worth of LEDs. At 72mW per LED that's nearly 4000 LEDs - the cost would be prohibitive. > 3. Would such lighting require: > A. a regular ballast; > B. one of the newer electronic ballasts; > C. a new type of ballast; or > D. no ballast LEDs require their own special form of ballast. The design problems in dealing with large LED arrays are not trivial.
> I was just browsing the internet and looking for a way to build my > own LED circuts and also find suppliers for all of the components. > My main goal is not for cave lamps, but for my lighting system on > my Jeep ( 12V back-up lights(white), brake lights(red), turning > signals(amber)). Multi-LED lamps sound a good idea for car (and bicycle) lights. Amber and Red LEDs are a lot cheaper than white ones. In fact you could fairly easily knock something up from red and amber LEDs, because you wouldnt need the same complexity of circuitry that we do for caving lamps, where we want to boost the voltage from a small battery.
This page, http://www.caves.org.uk/led/led-myths-2.html was last modified on Tue, 26 Nov 2002 00:00:00 +0000