forward voltage of LED diode

[shanmei]

I found all the LED diode have a minimal forward voltage of 1.7V. Anyone knows that whether there are some LED diode with forward voltage less than 1V, and the forward current is less than 20mA? Thank you.

 

[schmitt trigger]

Forward voltage drop depends on the LED wavelength.
IR diodes indeed have forward voltages of around 1.7 volt, blue diodes are over 3 volts.

But less than 1 volt?
No.

 

[shanmei]

Oh, that is the reason. Thank you.

 

[c_mitra]

Anyone knows that whether there are some LED diode with forward voltage less than 1V, and the forward current is less than 20mA?

Current is not the issue, it is the voltage drop. That is the barrier energy.

Say you have a forward drop of 1V. One electron crossing the barrier will get an energy of 1 eV - this is in energy terms approx 1.2um wavelength of light.

See for more information https://en.wikipedia.org/wiki/Photon_energy

And this is assuming 100% efficiency. If you have an IR LED, the minimum voltage drop will be around 1.3V (100% efficiency) to get a photon of 1000nm wavelength (typical for IR LEDs).

If you want 500nm wavelength, you will need a larger voltage drop: about 2.6V.

Add about 100-300mV extra for other losses.