Electronics guru required - dull down my LED tail lights

stevew_zzr · Post by **stevew_zzr** » Mon Mar 13, 2006 12:26 pm

http://www.toymods.net/forums/showthread.php?t=87 <-

"you cannot dim LED's PROPERLY by reducing the voltage driving them. They will dim possibly ~5-10%, and then they'll just shut down. To properly dim an LED you have to vary the current to the LED whilst maintiaining a voltage just a little higher than the forward bias voltage (usually the rated as "typical operating voltage").

To do this you need a simple transistor circuit using a very common 30c transistor and suitable resistors and a trimpot to vary current. I have done it before, but it's buried in the "celica box" somewhere....

in most cases, running your typical 3.0-4.0V operating voltage LED at around 20-50mA from your car you should use approx 570 ohm resistor."

Maty10 · Post by **Maty10** » Mon Mar 13, 2006 9:27 pm

Ahhh stevew_zzrbet me to it!

You can't vary the brightness of a LED by changing its voltage, that's a design goal so they can work on digital voltages with noise, etc.

Hence why they are used in flashlights, batteries can go flat, but you still get the same colour and (near) strength light. Unlike incandenct globes that go yellow and dimmer.

To vary a LEDs brightness you have to switch them on and off really really fast (hence the mention of a transistor).

Post by **dave#3** » Tue Mar 14, 2006 8:27 pm

Anyone want to buy four LED tail-lights ? Hardly used, one female owner

This is all getting way too hard

Stereo · Post by **Stereo** » Tue Mar 14, 2006 8:56 pm

dave#3 wrote:Anyone want to buy four LED tail-lights ? Hardly used, one female owner

This is all getting way too hard

Do LED's generate any heat? I thought that they didnt... and if not... why not cover the rear tail light with a perferated film that matches the paintwork..
The tail light will almost disapear until you turn the lights on... and they will be dimmed a whole bunch... but when you are braking they will be quite bright...

Or... how about having only ONE led? They are after all twice as bright, you would need to centre the bulb somehow if possible...

stevew_zzr · Post by **stevew_zzr** » Tue Mar 14, 2006 11:10 pm

Just go to a local Jaycar store or something like that, ask if they can help you with a simple transistor/resistor combo that works ?

YAPPA · Post by **YAPPA** » Wed Mar 15, 2006 6:25 pm

dave#3 wrote:Thanks Gos,

I assume "100k" is a 100 kilo ohm.

If ya ask me, a 100 thousand dollars is a fuggen huge price to pay for a tail light that will just fuk up ya power to weight ratio