How much does voltage affect the light frequency output of an LED?

Question

I have a large array of LEDs that I need to be true to their datasheet light frequency emission (ex 635 nm.) The LEDs require V_typ @ 20 mA ranging from 2.2 V to 1.2 V. Some are within 0.1 V of each other.

In the interest of minimizing the number of Zener power circuits I need to add, could I put both a 1.8 V and 1.9 V on a 1.8 V power source without much light frequency deviation? Any way to know how much or guess the direction of the deviation?

I just remember from past experience that over-volting orange LEDs color-shifted them to yellow. I never knew if this was a bandgap/voltage thing or just overheating LED caused it.

Answer 1

Use a ready made LED driver. Based on the number of LEDs and current needed, you can choose drivers available. An example is this from analog devices.

Depending n type of power supply you have, you can narrow down to a suitable LED driver.

You can also build a constant current driver using one opamp and a transistor. I can suggest.

• The wavelength will vary slightly when the temperature of the LED is varied. I have not come across variation in wavelength due to change in drive current

• Reference for wavelength vs temperature
  : https://dammedia.osram.info/media/resource/hires/osram-dam-3993183/LA%20G6SP_EN.pdf

Answer 2

You need to control the LED current, and let the LED choose its own voltage.

Typically, you use a constant voltage power supply somewhat higher than the highest forward voltage of the LEDs you are using. Add a resistor in series with each LED to limit its current to its typical value - generally somewhat less than the Absolute Maximum current listed in the datasheet.