I ran across this site because I was looking, unsucessfully, for reasonable 5mm white 5 to 10 degree LEDs and couldn't help answering. I'm probably repeating information that's already covered elsewhere, sorry.
I have been designing automotive LED lighting for some time now and have never seen a 20 degree 5 mm LED anywhere near 40 cd. Perhaps this is not a 5mm LED. There is no free lunch. There is a limit to LED efficiency. The only to increase brightness is to reduce the half angle or increase the power and the current is limited to 25 or 30 mA continuously for 5mm LEDs. You can of course increase the current significantly and the LEDs will work for awhile, which may be a bunch in some applications.
The lifetime of a car is considered to be 4000 hours (200k miles at 50 mph as I see it) so you you can knock quite a bit off the standard 100k LED lifetime. However, I haven't found any good information on the effect of overcurrent on LEDs, that is do all fail quickly, or a higher percentage fail. The specs say a certain percentage drop below 50% or 70% brightness over their lifetime. It doesn't say whether they are 1% below the threshold or off. I also know that ambient temperatures can get fairly high inside a housing so I don't push the specs.
$6.93 is an outrageous price. I have found that the price per light output favors the lowly 5mm led over fancier high outputs, especially if you have to add heatsinks.
If you go to leadingLEDs.com (for example) you will see 15 degree 12 CD 5 mm LEDs for $ 0.17 each in small quantities. These are offshore LEDs but I have had good luck with them. They all use the same LED chips so the question is the packaging. With a 100 khr life I probably won't be around long enough to quibble about "long life". The offshore website for leadingLEDs, LEDz has some good information on the lifetimes of various chips.
A 15 degree LED will light about 10' across at half or more brightness at 40 ft. This is probably too narrow for most automotive applcations, as aiming becomes a serious issue. Narrower yet and you probably need some servo controlled aiming device. At $0.17 per LED you are better off using gobs of 5mm LEDs with a wider angle and lower power. Most of the heat in LEDs is dissipated through the leads unless you use a fancy, large and expensive heatsink. I commonly use close to 100 30 degree LEDs for stop or turn.
I also have a simple single PNP transistor current control circuit. Otherwise if you try for efficiency and string your LEDs in strings with resistors so the resistors drop 2 or 3 volts at 12v they will drop 5 to 7 volts at 15 volts and the current will be much greater, about 2-1/2 times as much, so you either have dim LEDs at 12 volts or over current at 15 volts. The commonly accepted voltage for alternators is 14.5v but I have seen alternators pumping out 15 to 15.5v and once 16v.
- stephen
I hope this is the correct forum to ask this question. I saw this 5 mm LED on the besthongkong website:
