3 ms·
Fun fact: When you accelerate an electron across a potential of 4.5 volts, and then stop it suddenly, you get a photon with 4.5 electron volts of energy. That’
by fallingfrog 5y ago
Fun fact: When you accelerate an electron across a potential of 4.5 volts, and then stop it suddenly, you get a photon with 4.5 electron volts of energy. That’s why different colors have different voltage drops.
So a blue LED has about a 4.5 volt voltage drop, and a red LED has about a 2.2 volt drop. And a blue photon has about 4.5 electron volts of energy, at a wavelength of around 350nm, and a red photon has about 2.2 electron volts, at a wavelength of about 600nm.
- JKCalhoun 5y agoThank you. I had understood that the wavelength of an LED correlated with the voltage drop but did not know why. (I had just assumed it was a characteristic of the physical materials needed to obtain the various colors.)
- tyingq 5y agoExpanding on that a bit, generally, the shorter the wavelength the higher the voltage drop. So UV leds have the the highest, followed by violet, blue, green, yellow, orange, red, then infrared. Then white being a special case since it's typically 3 leds (r/g/b) and not one.
- jpmattia 5y ago> Fun fact: When you accelerate an electron across a potential of 4.5 volts, and then stop it suddenly, you get a photon with 4.5 electron volts of energy. That’s why different colors have different voltage drops. This explanation does violence to conservation of momentum, since \hbar / \lambda is miniscule for the photon compared to the electron. The correct explanation involves recombination with a hole across the bandgap, which is how momentum is conserved in the interaction, and the motion of the electron is not involved other than transport for electrons to find holes for recombining.