Question

Data:

The initial voltage was around 8.045 V after it was charged.

LED #1: Red, 1.55 V

LED #2: Orange, 1.81 V

LED #3: Yellow, 1.64 V

LED #4: Green, 1.77 V

Question:

How does voltage and color change going from LEDs with the highest phosphorous percentage to the lowest? Explain your data in terms of band gap energy. As part of your explanation, rank the LEDs in order of increasing band gap energy (lowest to highest).

Answer 1

Shorter wavelengths of light are made from higher energy photons. Red is longer wavelength / lower energy than Yellow than Green than Blue which is shorter wavelength / higher energy.

Now we have energy of the emitted photon is given by

E = hf = hc/λ.

So with this logic, higher the wavelength lower will be the band gap energy. So, to get the electron to hike up to the higher state, we apply voltage. Higher voltage = more energy.

Wavelength range of different color LEDs-

LED color	Wavelength Range (nm)
Red	625-760
Orange	600-625
Yellow	577-600
Green	492-577

So by this logic we have,
Red LED < Orange LED< Yellow LED< Green LED (LEDs in order of increasing band gap energy)