Ah!, its not as simple as that, as consider where would the sensor be?,
somewhere near the light I'll wager, so when the light comes on how's it
going to tell when its dark again?.

When it turns on, it does so only for a period, such as 15 minutes. Then it
turns off again. If it is still dark, it will relight. This appears to the
user as a very brief flicker.

Christian.