Why is the resistance of light-dependent resistors wavelength-dependent?

The resistivity of the semiconducting CdS in LDRs is dependent on the intensity of the incident light. This makes sense, given that the more photons (with sufficient photon energy) hit the material, the more electrons are excited into the conductivity band, and resistivity decreases.

However, it also depends on the wavelength (photon energy) of the light. I don't see why this is the case, given that in the photoelectric effect, only a certain energy is required to excite an electron, and if the photon energy is higher, the electron will simply have higher kinetic energy). Thus it would seem that the number of electrons released is not wavelength-dependene.

I found this question, which seems to cover a similar topic, but it doesn't deal with LDRs or semiconductors specifically.

• The active area is some thickness. The absorption coefficient is a function of wavelength. Combine the two and... Dec 13 '16 at 17:53