On Thu, 6 Jan 2000, David McDonald wrote:
> BA to establish and actively promote guidelines/standards for spotlighting
> birds, including maximum wattages for spotlights in various situations.
Power consumption (wattage) of the spotlight may not be useful because
the shape of the beam will have a significant effect on the light reaching
the bird at a given distance.
For example, I have two spotlights. One is a 30+ year old rugged metal
spotlight which consumes ~25 watts and a cheap new plastic spotlight which
consumes ~50 watts. However the old ~25 watt spotlight has a narrower
more focused beam and is signicantly brighter at typical spotlighting
distances.
Distance is even more important. The light reaching a bird will drop
(at least in principle) with the square of its distance from you. So a
bird 10m from you will receive (in principle) 25x the light of a bird
50m from you.
The relevant measure is probably illumination(lux) at minimum
viewing distance.
I must admit, I'm not worried in general about spotlighting birds
after reading Jack Pettigrew's opinion previously on birding-aus:
http://www.cse.unsw.edu.au/birding-aus/hypermail/1997/0544.html
A side note for the birding-with-children audience, I was dissappointed
with the cheap plastic spotlight (admittedly only $20) until I took my
4 year old son spotlighting, a couple of months ago.
He carried a torch but wasn't confident with just its light.
The "superfluous" light from the cheap spotlight provided enough
low-level illumination of the trail and surroundings to let him explore
confidently. We spent a happy 2.5 hours on Lady Carrington Drive in
Royal NP (Sydney), even though it wasn't a great night (spiders, moths,
sleeping WB Scrubwren, Bush? Rat, Brushtail Possum carrying young).
Andrew Taylor
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