does multiple lights = added output

J

james d

Member
Hi guys,

I'm just wonder, say if I got two hmi's at 1.2kw

Does that give me near the same output and throw as a 2.5kw hmi?

Will 5 1.2kw strung together give me the same output as a 6kw hmi OR is the throw bigger on these single units?

This method also applying to other types of lights.

Thanks!
 
In theory, yes. Doesn't mean it'll work out exactly that way in practice, especially when mixing brands.

Plus, it'll be affected by distance, flood/spot level, etc.
 
ok great.
@David W - Am I right in understanding you when you say that banks of lights WILL NOT give the same throw as a large light?

I am thinking about investing in several DIY 1kw builds is why I ask.
I have just got a nice digital ballast with a bulb rated at 6000k, I can get 5500k in the future. I have not tested this photographically but the cri rating on all e40 bulbs I can find are in the 60 range. Not sure if this will cause a problem until I test.


So If I can bank the light then this could prove effective in not having to rent out suitable HMI's light with insurance etc. if I have a bank of them my self.

The benefits mean also I could seperate them and spread them out. Attach the outputs to different power sources etc.

And then when needed, String them together for a larger light source.

One thing which might cause a problem could it be when exterior lighting and using a generator, striking 4+ 1kw hmi's 1 by 1 off a 6.5kw honda is going to be a problem?
 
The problem you'll run into with a DIY fixture is that you will never get the same beam quality that a real HMI PAR or fresnel will give you (unless you're retrofitting an existing tungsten fixture), that is, highly focused and easily controllable. This tends to be more preferable if you have to light up larger areas. With a DIY light that will have a very wide spread, you can't always back it off far away enough to light a space evenly while still having a sufficient level of light to expose. For soft light, ganging up several 1k metal halide lamps through a thick diffusion could be a real alternative to renting a 4k though.
 
Photometric data is pretty difficult to interpret. The real critical area to think about is that whatever lighting you are using, and wherever you put it, to compare brightness you use a meter and it tells you the amount of light that is falling on it. What rarely works is to assume that the power consumption of a lightsource is an indication of how much, and what quality light come out. Two 1.2s vs one 2.5 can be compared in terms of the power they are consuming, but having two light sources introduces variables that mess up the experiment. Firstly, large Fresnels have larger lenses, which let out more light. Comparing two light sources with one being double the wattage often doesn't produce much extra light to the eye. A 650W Fresnel looks brighter on an object 6ft away than a 1.2K on something 12ft away. If you put two 1.2K discharge sources next to each other, then the light landing on a person goes up, but not in any shadows you see. The nose, for example produces a grey shadow, not a black one - so the subject looks different. A small focus adjustment to narrow the beam can produce the same brightness increase as the swap to 2.5 from 1.2K. So the paper 3dB gain in brightness from doubling the power isn't really that much, as many people assert a 2dB increase or decrease can't be detected by most people, only a meter. A row of 1K lights produces an effect totally different to a single 5K, but uses the same electricity. It certainly does not look the same.

You use the word 'throw'. I expect you are really talking about distance. As in, you have to use a distant lighting position by necessity, so 'throw' usually dictates a narrower angle beam, simply to not stick light where it is wasted, and to concentrate the beam. Look at the charts from some of the Arri Fresnels - you can see that even a gradual narrowing of the beam width ups the light level at the measuring position drastically. So you can see a spotted down 650W can be subjectively brighter than a flooded 2.5K discharge! When I'm lighting something big, I look at the subject, and the places I can place the light source. The distance will indicate the kind of power I need. I would never double up a light source - I don't think I have ever done that. If there is a fixed budget, then one of the features of the lighting design is placement compromise. If you need more light on the subject, you can move the source in closer, you can narrow the beam width, or up the output. Deciding which will work best is a bit of an art. I remember years ago, a 'name' responding to a student question about lighting equipment. "what would you do if your key wasn't bright enough?". He looked confused and just said - "get a bigger one".
 
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