A bulb emits light of λ=4500Å . The bulb is rated as 150 watt and, 8 percent of the energy is emitted as light. How many photons are emitted by the bulb per second?

Energy of one photon =hcλ                                  =6.625×10−34×3×108J4500×10−10=4.42×10−19JEnergy emitted by the bulb =150×8100J           n×4.42×10−19=150×8100J