From Planck's hypothesis, the energy of a photon, of frequency vis E=hv=λhc
where c is speed of light and a. the wavelength.
In the visible part, red colour has maximum wavelength λ=8000A˚ ∴E=8000×10−106.6×10−34×3×108
Also, 1eV=1.6×10−19J ∴E=8000×10−10×1.6×10−196.6×10−34×3×108=1.547eV