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# Calculating lighting needs

Discussion in 'Lighting and Electrics' started by hemismith, Oct 22, 2010.

1. ### hemismithMember

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Sorry to post yet another thread -- I found a good web site and did some more reading, but a lot of thoughts are going through my head and I'm still as confused as ever (although that may never change).

When I look at the size and illumination of the lighting area, I'm wondering how much I factor angles into that. For example, from a 45 degree angle the circle becomes an oval 1.4 times as wide. Do I reduce the illumination figures accordingly, or do I assume that the surfaces they are hitting (i.e. sides of faces) are also angled towards the light and therefore no reduction is necessary?

And what is a good max illumination figure to shoot for? 100-200 fc?

2. ### shibenWell-Known Member

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It is always good to take your angles into account. A program like vectorworks will show you the pool of light at a given focus point from a given instrument. The main thing you want to think about is how many areas you NEED for control reasons. For example, a show I designed over the summer needed to have 13 areas for control reasons, so the instruments I chose were in response to that need, rather than "I can cover this stage with this instrument". So what you should do is figure out how many areas you need to have to control, then figure out what lights will cover how much area, with the ovals taken into consideration, and then get those.

The max illumination sounds about right, I like to be able to go as high as possible, because you can always back a dimmer off and make the light less intense, but you cant push a light higher than its max output.

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3. ### FooterSenior TeamSenior TeamPremium Member

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Also, remember that you are not lighting the floor, you are lighting 6' above the floor. When working on a section, always draw a line at 6' and build your areas and select fixtures based on that.

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4. ### hemismithMember

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Thanks. I'll have to check out lighting design software when I get a chance.

Yes, I do typically calculate needs based on areas -- my next big show has 14. But right now my immediate need is just to light the whole stage. But this brings up another thought: If I pick one light for one area and another for a different sized area, the intensities will be different. True, I can alway back off, but unless I specifically want a different intensity it seems I could just use the same light with an iris or shutters to change the area covered.

5. ### hemismithMember

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Good reminder, thanks!

6. ### shibenWell-Known Member

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An even easier solution is to try and make all your areas about the same size. I try and go for an area size that I can use a 36º S4 to fill it, usually about an 8'd circle. The problem with shutters and irises is you dont actually get the same intensity. When you iris an instrument down, you make it a lot dimmer. Backing the hotter light off is usually the better option.

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7. ### hemismithMember

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Thanks, I like that approach.

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