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 600 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?

Answer 1

(a) frequency = c/(wavelength)
(b) 75 W/(h*f)
where f it the frequency and h is Plank's constant.
(c) certainly not. Frequency does not depend upon brightness. Photons per second does.

Answer 2

By the way, your "posted by" name is an incorrect statement, which disagrees with the facts and the question itself. What is that all about?