Lumens vs GN

Hi guys,

I know this is effectively comparing apples and bananas but here goes :-

A friend of mine is in the process of setting up a small studio and has been advised to get himself a couple of 500W halogen floodlights.

Wikpedia says that halogen lamps produce about 19-20 lumens/watt so it looks like he'll be getting circa 9500-10000 lumens.

How does this equate to a Guide Number, I'm sure there must be a loose correlation somewhere as exposure for all lighting is based on :-
Duration of exposure
Light Intensity
Distance of subject from light source
Etc

So all comments (especially those which help solve the riddle) are most welcome

regards
Bernard

You can't make an equivalent. With constant lights, like halogen, you can alter the shutter speed to change the exposure. With a flash, the shutter speed doesn 't do much to the exposure of the main subject, unless there is some other form of lighting also involved, which is kind of unlikey in a studio set-up.

On the other hand, if I was your friend, I'd look at full spectrum fluorescent bulbs for studio work. The halogen type lights generate so much heat that you have to be really careful when getting them close to your subject(s). Burns can be a very serious problem. The halogen bulbs are also very fragile while hot, which is a pain when handling the lights.

On the other hand, you can easily use umbrellas and softboxes with the fluorescent lights. Softboxes are a definite fire hazard with the halogens, and the umbrellas will "yellow" in a very short time due to the heat.

Guide Numbers are not usually quoted for any kind of studio lighting since output will be dependent on what sort of modifier is on the lamp e.g. reflector type, brolly, softbox etc.

Yves points out all the disadvantages and generally contiuous lights are really for video. 500 watts isn't really very much at all and pro ones will cost as much if not more than studio strobes.

If he really wants continuous light then cold fluorescent migh be a better bet eg link at £236

but this is almost the same price and will offer much more versatility link

Thanks Yves, Ken

As I said "apples & bananas".

You've confirmed just about everything that I'd commented on during the discussion I had with him. But as it was over a pint or two it might have been a good idea so I thought I'd ask as it got me thinking.

I certainly wouldn't consider them in my garage, there's too much wood dust and shavings everywhere. His garage looks like the set for an operating theatre


regards
Bernard