[OT] Anyone experienced with white LEDs?

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Tue Feb 4 18:40:01 2003

>From: "Roger Merchberger" <zmerch_at_30below.com>
>
>I'm looking at building a personal lighting project possibly using white
>LEDs instead of regular miniature bulbs, and as I browsed the Mouser
>catalog, I got a whole lot more confused than less...
>
>I'm trying to get the maximum amount of light for current expended, and the
>numbers seem to be nonstandard, or at least not enough info is provided... :-/
>
>Example:
>
>P. 217, "Super Flux LED Lamps"
> The white one shows at 20mA it will put out 400-600 "Iv (mcd)"
>P. 216, "Blue & White LED Lamps"
> The brightest white they have is listed as: "2200->3200
> "Luminous Intensity" but with no mention of current or value
> (mcd? ucd? )

Hi
 I'm not sure what "Luminous Intensity" means but mcd means
milli-candles and ucd means micro-candles.

>P. 199, "Thru-Hole White LED Lamps"
> "Luminous Intensity" ? current would output 1.7->2.3->2.6
> (min/typical/max) mcd...
>
>
>and on P. 206, there's a few colored LEDs output listed as "Foot Lamberts"...
>
>And Digi-Key has these Surface Mount Incandescent Lamps... :-O The look
>cool, but how hot do they get? (It's a very small installation area... It's
>still an idea I'm forming, but if it works out, it's a *kewl* idea...)
>
>Any good websites w/info on how to figure out how many LEDs I'd need to
>make about a 40W (or more) lightbulb worth of light?

 This is not so easy to figure. You need to know how efficient
the LED's are, relative to standard bulbs. It seems like I saw
something that said that LEDs were not quite as efficient as
fluorescent lamps but still better than incandescents. If we figured
them at twice as efficient, you'd need 20W's of LEDs. Watts is
just the current times the voltage. You figure this for each LED
and add them all together. LEDs do require a circuit to limit
the current. When you figure your total light output, you don't
count the loss in the control circuit. Of course, for the final
tally, you'll need to include this as well.
 When driving a number of LED's, it is better to drive a large
number in series because you only need one current limiting
circuit. The count of LED's would depend on the voltage source
you have available. You'd have the total LED voltage plus
the drop needed across your current limiting cicuit.
Dwight

>
>-- Also, my college electronics braincells are rather weak, as I can't
>remember if the wattage rating means "total dissapated wattage" or "total
>wattage of the circuit branch it's in"... [1]
>
>... I'm getting too old for this ...
>
>Any help/pointers would be *massively cool*...
>
>Thanks!
>"Merch"
>
>[1] - I want to use SMT current limiting resistors [2] (fewer holes to
>drill...) and the highest wattage ratings I can find is 1/8W... in a 6V
>20mA circuit it's running real close... (I could run ~17mA to get a margin
>of error... but I want the max light I can get...) RatShaq has 1.2A 6V
>wall-warts for a reasonable $, and I wanna build a "different" light
>fixture. Of course, I want a *usable* light fixture... ;-)
>
>[2] - I wish I could find SMT white LEDs... :-/
>
>--
>Roger "Merch" Merchberger -- sysadmin, Iceberg Computers
>zmerch_at_30below.com
>
>What do you do when Life gives you lemons,
>and you don't *like* lemonade?????????????
Received on Tue Feb 04 2003 - 18:40:01 GMT