Red has highest wavelength and violet has lowest wavelength. We know that relationship between energy as follows.
E = hv = h\(\frac cλ\)
h and c are remains constant.
∴ E ∝ \(\frac 1λ\)
Energy is inversely proportional to wavelength. Red coloured light has lower energy and least intensity. So red coloured lamp is preferable as bed light.
