AndyB

I have two questions about LEDs and I am posting them together since I think the same person(s) could answer both.

1) What color amber/yellow LED would best match the Z's turn signals / parking lights in front?

Amber 598 nm center wavelength
yellow orange 611 nm
amber yellow 595 nm
yellow 588 nm
red-orange 624 nm

something else?

2) What is the best way to build a circuit for several LEDs? I can think of two obvious ways off the bat.

For the example assume the LEDs are 2V Vf at 50 mA and I want to hook up 3 of them. (nice round numbers for the example)

For a 12V system I could wire in series a 120 ohm resistor and the three leds. (total power .3 watts). ie.

+12V---R---LED1--LED2--LED3---GND

OR I could hook each LED in series with its own 200 ohm resistor. (total power 1.8 watts)

+12v---R--LED--GND

Which circuit would you recomend and why?

To me it seems option 1 costs less money, fewer parts, and less power. But it also sums the variances in the forward voltages of the LEDs. (hard to contrl the brightness)

Option two is a little more work, parts, and money, but seems like it would be a little more robust in design.

Please let me know what you think.

ares

iTrader: (2)

I use orange LEDs at wavelength of 605. I find them to be a close match.

then again I havent tried those others your quoting, so they might be closer.

I use the first method, mainly because my application doesnt require that. brightness isnt variable, they are on/off with the turn signals or parking lights, no other controls, if I planed to vary the current to it, then yes, I think I would use the second layout. resistors are cheap anyway, even radioshack has em for 20cents.

DIGItonium

iTrader: (1)

I'd think sticking to Amber LEDs would be the way to go since they conform to SAE standards.

For my turn signal bulbs... I should've given the Luxeons 350mA instead of ~100mA current since the flashing doesn't make it generate much heat. Someday.... :-D

AndyB

Well I found an electrical engineer at work to talk to. (A real EE wiz).

He suggested circuit 1 for a very good reason. He said that if the LED will be near each other then putting them in series will ensure they get the same current. That means they will have (roughly) the same brightness.

Since each LED and resistor can have some variance, circuit style 1 will help make them match.

Just figured I would share that.

DIGItonium

iTrader: (1)

He's correct on that. To figure out how many LEDs to connect in series given the voltage supplied. Get the LED voltage spec like (2.8V... take the max voltage from source and divide by 2.8V drop) The resistor is current limiting, and I recommend using at least 1/2 Watt to dissipate enough heat.

For my Luxeons, I'm using ceramic resistors (blue/grey looking) that can dissipate a maximum 1W.