Many considerations enter into the choice of a detector for radiative measurements. If time
response is important, photon detectors are significantly faster than thermopile or thermistor
detectors, and therefore have a much wider frequency response. Photodetectors saturate, while
thermopile sensors may slowly change their characteristics over time. Some instruments have
variations of sensitivity with the incident angle of the incoming radiation; this factor may be
important for solar insolation measurements. Other considerations include wavelength sensitivity,
cost, and allowable operating temperatures.