Wiring LEDs

Support Q&A
1

Before I let the magic smoke out of a bunch of stuff by just trying things, I thought I’d ask here.

I have a situation where I want to light up several LEDs to the same brightness. There are 4 different LEDS: Part numbers 350-2979-ND, 350-2956-ND, 350-2595-ND and 350-2121-ND, Green, Red, White and Yellow. They will be powered by a 12 volt supply. I would like them to show as close to the same brightness as possible. They all show a different voltage and current requirements. Using Ohm’s law, I calculated the various values for resisters

Part Number   Color    V    I      Resistor  Resistor color
350-2979-ND   Green   1.9  0.007    1714     Brown-Grey-Red
350-2956-ND   Red     2    0.02     600      Blue-Yellow-Brown
350-2595-ND   White   3.3  0.03     400      Yellow-Red-Brown
350-2121-ND   Yellow  2.1  0.02     600      Blue-Yellow-Brown

When ordering the resistors, I’ll recalculate to reduce the current by 10 percent to prolong device life.

Am I doing this correctly? Is 10% enough? Will the brightness be the same between the colors?

2

Hello,
You are correct the 10% is a good way to extend the life, the problem is the Millicandela Rating of the parts are all different so you can get the parts to all turn on, but the brightness will not be the same.

3

Unfortunately no, human eyes are far more sensitive to some colors than others. So different color LEDs producing the exact same millicandelas of light will appear to be different.

The only practical solution is to ball park the values like you’ve done, try it out, then adjust the resistor values up on the ones that seem too bright.

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4

Hi bart
The best way I’ve found is using a potentiometer on each LED for initial testing. Once you have the LED brightness all set where you want them and verify they are running within current/voltage specs, disconnect the pots from the circuit and measure the resistance values. Then you will know exactly what fixed resistance values you need.

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5

Thank you all for the quick responses.
I was aware of the human eye factor. Like a lot of things, it seems the older the eyes get the more pronounced the situation gets.

Guess I’ll just play with some values and see how it goes!

Bart

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