How can a small electric current produce a particular color of light?
An LED is a forward-biased semiconductor junction. Electrons from the n-type side and holes from the p-type side meet in the active region. When an electron recombines with a hole, the lost energy can leave as a photon. The material's band gap sets the approximate photon energy, so changing material changes the color. Current changes how many recombination events are represented per moment; it does not make each photon travel faster.
Select a part. Change a control. Follow the motion.
Material selects the approximate photon energy (and therefore color); forward current controls the rate of charge delivery and, in this schematic, the rate of emitted events.
In this model, what changes when you raise current while keeping the material selected?
The blue n-type region supplies electrons and the orange p-type region supplies holes. The central band is an active junction where they may recombine.
Raise current
Increase forward current. More charge-delivery markers and more highlighted recombination events appear per cycle in this teaching model. The current is a rate input, not a photon-speed control.
Choose a material
Select red, green, or blue material. The band-gap label and emitted-color swatch change because photon energy is approximately the band-gap energy: E ≈ hν.
Separate rates from energy
Current mainly changes the number of events represented. Material changes the energy/color assigned to each event. Real brightness also depends on efficiency, temperature, optics, and device construction.
The main parts
p-type side
A schematic region with mobile holes, shown as open orange circles.
n-type side
A schematic region with mobile electrons, shown as filled blue circles.
Active junction
The region where an electron and hole can recombine; the drawing is not to scale.
Emitted photon
An orange/blue ray marks an emission event. Its path is schematic, not a measured trajectory.
LED terminals
The applied forward-bias path supplies charges to the junction; conventional current direction is not drawn as electron motion.