How ocelli differ from compound eyes

How ocelli differ from compound eyes:
Ocelli possess only a single structure inpite of having multiple units. That’s why they are called simple eyes. Adult insects possess ocelli along with compound eyes. Ocelli are found at their back or face. Dragon fly and may flies also have ocelli, these appear as tiny swellings.
Functions of ocelli:
? Ocelli are helpful in detection of small changes in light intensity.
? Ocelli can affect changes in behavior because it has been found that they are associated with some largest neurons of the nervous system.
? Ocelli control circadian rhythms in some types of insects by performing activity of light detection that falls on their body and then nervous system conveys message to different regions of the body.
? In an experiment performed on Cockroaches it has been found that the stimulation of light caused by ocelli has the ability to alter the the features of the optomotor performance .