Actually, the historical discovery of quantization is that Max Planck postulated that light was quantized in order to get the radiation spectrum of black bodies to come out correctly. Albert Einstein then argued forcefully for this quantization to be a real phenomenon rather than a mathematical curiosity ( trick) in the analysis of the photoelectric effect. The quantization of light energy means that, according to Planck's formula
Energy = constant x frequency of light.
The constant is 'Planck's constant' and the frequency is measured in cycles per second. You can find out how much energy is carried by any photon in the electromagnetic spectrum just by multiplying its frequency of vibration by Planck's constant.