The time required for the detector output to go from the initial value to a percentage (e.g. 99%) of the final value. In the case of an exponential behaviour of the detector can be related to the time constant . The rise time is the time required for the detector output to vary between given percentages (e.g. from 10% to 90%) of the final value. Similarly, the fall time is the time required for the detector output to vary between given percentages (e.g. from 90% to 10%) of the initial value.