On Tue, 05 May 2009 18:01:34 +0000, The Medway Handyman wrote:

Yerbut, nobut, yerbut. At the front of handyman towers I have a dawn
dusk lantern (no PIR) with an 11w thingy bulb (sorry, lamp) and about 8'
away on the front of the garage I have a 500w halogen light (manually
switched, no PIR).

If I'm loading the van at night & switch on the 500w jobby, the dawn
dusk goes out, until the 500w is switched off again. So (a) how come
the 11w lantern doesn't switch itself off evey time it switches on and
(b) its seems to react to a 500w halogen just like sunlight.


The sensor on the 11w dawn/dusk will be a very primitive (i.e. cheap)
photocell used to trigger a solid state switch. All it measures is
brightness - it doesn't care what it is, unlike solar cells. The normal
(cheap) Cadmium Sulphide photocell is sensitive to the whole visible
range and a bit further, into the infra red.

Your 500W halogen light will be kicking out a LOT of infrared (or, as
many people know it, heat).

The reason it doesn't switch itself off is (usually) simply because the
sensor is let back a bit into the case - light travels in straight lines
so its own light doesn't reach its own sensor.