1. The problem statement, all variables and given/known data Under favorable circumstances the human eye can detect 1.0e-18 J of electromagnetic energy. How many 600-nm photons does this represent? (Modern Physics, Arthur Beiser, 6th Edition, Pg. 89) 2. Relevant equations My answer is unreasonably low. My mistake is probably very simple, but I'm not sure what it is. Any ideas? 3. The attempt at a solution First, I attempted to find the energy in a single photon with a wavelength of 600nm. Since E=hf, I simply multiplied h and f. I found f by the relationship f=c/lambda. So, (6.626e-34)(3e8)/(600e-9) = 3.313e-19 Then, I just divided the total amount of energy by this amount (the amount of energy in a single proton). (1.0e-18)(3.313e-19) = 3.02 I'm guessing that the eye can detect more than 3 photons at a time :-) but I'm not sure what I'm doing wrong. Help!