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Re: Osram HWL E27 lamps? -- or - Watts hot and Watts not

> HID lamps tend to run fairly hot anyway. If water
> splashes on them they 
> can shatter. There is also some concern about UV
> radiation. A shield is 
> normally used with these lamps to address these concerns.

All good points, but he first one can be a bit
misunderstood.  Aquarium metal halides and fluorescents
(PCs or others) are not especially hot compared to other
bulbs of similar wattage.  In fact they are terrifically
cooler than incandescents of similar wattage.  There are
some HID street lamps that run cooler at the same wattage
as fluorescents and metal halide HIDs, but you'd never want
one of those steetlamp bulbs on an aquarium -- they only
have one color from the spectrum.

Within each type of bulb, certainly there is some
variation.  but, that is relatively small especially in
light  of (excuse me) other relevent factors concerning
aquarium temps, like open or closed top, fans (and the
variation in effectivenes of different fans is tremendous),
room temps, lighting periods, other heat sources such as
filters/pumps, etc.

General rule of thumb: what puts a lot of heat onto or into
your aquarium when dealing with lights is the wattage. 
More specific rule of thumb:  multiply the watts by 0.65
and that is a rough estimate, in watts, of the heat you
have to deal with -- the other 35% of the input energy is
given off as light above the infrared frequencies.  

Generally, when determining whether a lamp is hot or not,
it's not the color-kelvin or kind of bulb, it's what's the
watts that matters.

Scott H.

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