1. The problem statement, all variables and given/known data You need to design a photodetector that can respond to the entire range of visible light (400 nm - 700 nm). What is the maximum possible work function? 2. Relevant equations E = hf = hc/lambda 3. The attempt at a solution For 400nm, I got E = 3.11 eV and for 700nm I got 1.78 eV. The solution is that the maximum work function is 1.78eV or less, and I do not understand why because 3.11eV is beyond the threshold for 400nm light to emit right? So shouldn't the answer be 3.11eV or greater?