# LED

Discussion in 'Electronic Design' started by Jennie, Oct 5, 2004.

1. ### JennieGuest

I have a FR200 radio with a light bulb attached. I am looking to hook up a
LED that is the best energy miser.

I am using a 5mm LED that is rated 20mA and 3.6 Volts - radio shack

FR200 = 4.5 Volts 3 AA Batteries at 1.5 each...Volts is series Volts
increase and Amps stays the same.

R = (Vs - Vr) / I

R = (4.5 - 3.6) / .020 = 45 ohms

What is the most energy miser bright LED out there? One to give me lots of
light time?

2. ### JennieGuest

Is this the right newsgroup to ask this type of ?

3. ### JennieGuest

Where are the high efficiency leds?

4. ### John PopelishGuest

You can operate any LED at a current well below its specified maximum,
with an almost proportional decrease in light output. Experiment with
the ones you have with current at .01 and .005 amp and see if the
light is bright enough. The only way yo make the battery last longer
is to find one that has high efficiency, so you can run at the lowest
possible current.

5. ### John PopelishGuest

sci.electronics.basics would be better.

7. ### John PopelishGuest

LEDs are sold many places. Where did you get the last one? The key
specification is the luminous intensity (usually specified in mcd or
millicandelas). Divide that number by the specified current and you
get millicandelas per milliamp. This is the conversion from current
to light efficiency.

For example, these LEDs sold through Digikey have the following specs:

http://rocky.digikey.com/WebLib/Fairchild/Web Data/MV8W00.pdf
typical 2500 mcd at 20 ma, 125 mcd/ma.

http://rocky.digikey.com/WebLib/Lumex/Web Data/SSL-LX5093XUWC-TR.pdf
typical 2300 mcd at 20 ma, 115 mcd/ma.

Whatever kind you get, run it at the lowest current that gives enough
light.

8. ### JennieGuest

MCD 1100 at 20mA, 55mcd/ma Is the lower the number, mcd/ma, a more
efficient LED?

9. ### John PopelishGuest

No. Millicandela is about 1/1000 of the light of a candle. More MCD
is more light (what you want) for the same current (what you have to
pay). The same way higher miles (what you want) per gallon (what you
have to pay) is a more efficient automobile.

10. ### JennieGuest

Thanks, where is a good explanation of how a led works, etc....

11. ### Jonathan KirwanGuest

HP's 2nd edition of "Optoelectronics/Fiber Optics Applications Manual." (If you
can find them after I sucked up a dozen of them from various sellers on the web
last year and sent them to people I knew would be interested.)

Jon

12. ### ClarenceGuest

http://csm.jmu.edu/physics/hughes/APL_66_115.pdf

OR

http://www.engineering.vcu.edu/fac/morkoc/learning/science.pdf

AND

http://www.lumileds.com/pdfs/protected/AB12.PDF

OR if you really need it and will pay for it.

http://ao.osa.org/abstract.cfm?id=25107

16. ### Rich GriseGuest

Some time ago, there was a thread about letting a big cap discharge
through a LED, and "does it dim continuously, or wink out at the end",
so I did the experiment. From 20 mA down to 10 I didn't see any
noticeable change in brightness (probably would have if I'd had 2),
and it gave light "smoothly", all the way down to 0.

So do some experiments. I wouldn't be surprised if there's a LED
that would give you a usable indicator at just a couple of mA.

Good Luck!
Rich

17. ### Spehro PefhanyGuest

My super-greens are usefully bright (under room lighting, narrow
angle) at just 250uA.

Best regards,
Spehro Pefhany

18. ### JennieGuest

Some LED's glass is so distorted the light has to be distorted too..

19. ### JennieGuest

Where do u get the LED's?