Hello,

Perhaps the following pages might be of interest:
https://micro.magnet.fsu.edu/primer/lightandcolor/ledsintro.html
https://electronicsclub.info/leds.htm
http://www.gizmology.net/LEDs.htm
https://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/

Bertus

 

When I saw an LED for the first time in the '60ies I joked that its junction was red hot!

I still have some 70's LEDs that about all they do is glow red. Low lumen visual indicator that would be useless in bright sunshine.

 

First father-in-law gave me a beautiful LED watch back in late 70's. All you had to do was push a button to see the numbers. In the shade. Forget reading it in daylight. And the battery had to be changed quite often too. No wonder why he gave it to me. He didn't want it.

LED's have come a long way since then. I just wish we had these super-bright LED's back then. THAT would have made a huge difference in a project we were building way way way back then. An LED mounted on a spinning plate being driven by an audio signal. Every time the signal went positive the LED would light. Its brightness would depend on the amplitude. The effect was really cool - especially if you'd been smoking an illegal substance (not advocating for smoking of any kind - or vaping). We had to turn out ALL the lights and wait till after dark to enjoy the show. Bruce Hornsby usually put on some of the best shows, and he never had any idea he was doing so. Piano music seemed to produce some of the best effects.

Anyway, LED's are fun to mess with. I have several jars of different sorts. 5 mm, 3 mm, rectangular, multi-color LED's. Surface mount and through hole. Granddaughter went to a "Lighted" skating party. She wanted to put an LED flashlight on the toe of her skates, like headlights. She handled that project but I hung a cheap vest with small batteries in the pocket with LED's forming a pattern on the back. She would have won first place but she admitted her grandpa made it for her. She got honorable mention. Kids!

 

So as I thought, different color of LED uses a different current and voltage. For making my circuit, with different colors of LEDs, I would have to convert the right voltage for the different colors of LEDs, right?

A better way of thinking about different LEDs is that they don’t use a different voltages, but rather they drop different voltages.

What different LEDS use is different currents. And if the wrong current is provided, the LED will fail.

Thus, current must be limited when using LEDs. There are many ways to do this, but the simplest is with a resistor - a current limiting resistor. To calculate the appropriate resistor, we use Ohms law.

Like this;

• Vs is the supply voltage
• Vf is the voltage drop
• I_led is the desired current
• R is the resistor value

This is the equation to calculate the resistor:

R = (Vs - Vf) / I_led​

Here is an example for a red LED that drops 2V and needs 10mA. The LED circuit is supplied with 6V

R=(6-2)/0.01
=4/0.01
= 400Ω
​

 

What they "really" do is the Voltage (electromotive force) adds energy to the substrate (the voltage drop across the LED) and "pushes" the valence electrons into a higher orbit which they cannot sustain. As the electrons fall back into their valence orbit they release the added energy as light.