The Night Eye will switch the day night function of the HabiStat Day/Night Pulse or Dimming thermostats on and off. It does this by sensing the light level. When it is light the day time temperature will be set and when it is dark the lower night time temperature will be activated. The difference between the on and off levels has been adjusted so that the unit does not flicker at the triggering point nor will it switch on and off due to minor variations in brightness. The Night Eye should not be used with anything but HabiStat Day/Night Thermostats. The output plug is specifically matched to fit these thermostats. Under no circumstances should it be removed. Night Eye units will often replace the time switches that have been used to regulate the day/night cycle with day/ night Habistat thermostats in vivaria.