A 75 W light source consumes 75 W of electric power. Typically only about 5% of this energy is emitted as visible light of wavelength 555 nm. (a) Calculate the frequency of the emitted visible light. (b) How many photons per second of visible light does the source emit? (c) Is the frequency of light the same thing as as the number of photons emitted per second? Frequency, Wavelength & Speed: Frequency (ν) of light wave is the number of waves emitted by light source. Wavelength (λ) of light wave is the distance traveled by the wave in one complete cycle. Speed (V) of light wave is the distance traveled by light in 1s. We relate these quantities through equation given by: V=νλ. Energy of photon emitted by source of light is given by: E=hν. (h is Planck's Constant and its value is found as: h=6.624J.s) Energy of photon can also be written as: E=chλ