On Sat, 11 Feb 2017 08:10:58 +0000, Brian Gaff wrote:

Might also be a nice idea to have some silica Gell inside as well.
However, some floodlights that look like they were built to withstand a
nuclear attack on a nearby 'listed' building still get water inside,
apparently, so I think the point is that there will always be some
moisture in sealed units.

Unless you can make the weather seals *gas-tight*, moisture will
eventually accumulate inside such fittings. Silica-gel will only delay
the inevitable unless you include a heating element to dry it out on a
regular basis.

Aside from the issues of ingress by suicidal flora and fauna, it's often
best to have as much ventilation as possible without compromising
protection against horizontal driving precipitation. In some locations,
this might be defeated by the more severe forms of precipitation which
can be driven by up-draughts a considerable way towards any exposed
connections taking shelter from the elements in such an 'open air'
protective shroud.

One thing to consider, if adding a couple of 3 or 4 mm drain holes in
something like a PIR controlled 300 or 500 watt halogen security
floodlight, is the possibility of rainwater being rapidly sucked into the
enclosure when the lamp switches off causing a rapid drop in temperature
which generates a vacuum. The resulting spray could well impinge on the
still hot lamp's envelope causing it to crack or shatter from the ensuing
localised rapid cooling. Even something as apparently humble as a drain
hole needs to be properly engineered if you wish to minimise interference
by Murphy of "Murphy's Law" fame.

The modern world of manufacturing seems to be tackling the issue of
Murphy's Law by, in effect, waving two fingers at Murphy and saying, "We
can make them faster than you can break them!" Things can be designed to
be proofed against Murphy's Law, it's known in the trade as "Over-
Engineering", something not normally countenanced by the "Bean-Counters"
so we rarely see such wonders in real life these days. :-(

--
Johnny B Good