The energy of each photon is given by E=hv, where E = energy, h = Planck constant and v is the frequency.

The relationship between frequency (v and wavelength l) is given by c = vl where c = speed of light. From this it can be seen that v=c/l so E = hc/l.

The difference between intensity and energy can be best shown in the photoelectric effect. Shining of very bright light of low energy (towards the red end of the spectrum) produces no electricity - a weak light of high energy (blue end) produces an electric current.