Lighting calculations

[AndyJones]

Hello everyone

 

I'm doin an event in a venue, were I know how high my lighting bars are, and were abouts I want my light. I am planning on using lots of parcans, but I want to know how big the beam on the floor will be. If I am using cp62's is there away that I can work out the size? bearing in mind that it isn't a "circular beam"

 

for example:

 

lamp

|

|

|

|5m drop

|

|

|

|____________________ 6m away is were I want the beam

 

I presume I use trig to work out the missing length, but then what?

 

Hope this is clear to everyone, if not I shall draw some pretty pictures.

 

Thanks

 

AndyJones

 

P.S could the answer go on the Wiki?

[Tomo]

Have a read of the Blue Room wiki.

Then do some trigonometry.

[3guk]

or if you are lasy, and IIRC http://www.paul-pelletier.com/LDCalculator does it for you with relative ease !!

[ben.suffolk]

I presume I use trig to work out the missing length, but then what?

 

I think you will find with a right angle triangle Pythagorean theorem is all you need to get the distance, not trig.

 

So distance squared = 5 squared + x 6 squared = 25 + 36 = 61

 

So distance is the square root of 61 = 7.81

 

Then A bit more math with the beam angle, and bobs your uncle. Mind you if your beam is not circular then it will be a bit more complex. Not knowing the beam angle for a cp62 without having to look it up I'll leave the next bit for somebody who does know what it it.

 

Ben

[woody74]

Have a read of the Blue Room wiki.

 

Based on his post script, kinda' sounds like he did...

 

I keep a simple formulated spreadsheet handy so I can enter the trim height and X dimension and it gives me both the throw distance and field diameter for my commonly used fixtures.

 

-w

[Tomo]

Are you honestly telling me that you don't understand basic trig?

 

That's GCSE maths, and pretty essential for lighting when everything is thought of in terms of beam angle.

 

Basic Trigonometry

The bit you need is under "Basic Definitions" - Tan A = Opp/Adj (the diagram makes it clearer)

 

Light pool radius = Tan (beam angle/2) * Distance to centre of pool

 

For a non-circular beam, do the equation twice - Once for the narrow dimension and once for the wide.

 

Life gets more complicated if you are hitting the stage at an extreme angle, but most of the time you can intuit that effect sufficiently accurately.

[Oovis]

or if you are lasy, and IIRC http://www.paul-pelletier.com/LDCalculator does it for you with relative ease !!

 

Dead link, I'm afraid. You need this one; here

[Tomo]

http://www.paul-pelletier.com/LDCalculator...culatorPage.htm

[Oovis]

Argh. Must edit my posts faster :unsure:

[AndyJones]

I know about trig, and Pythagorean, I simply mixed the two up. my quetion, now that I have thought about it abit more, was how do the calculations differ for oval beams, but the question has been answered-thanks to everyone!

 

Andy Jones

[David A]

The practical way is to borrow one of the lights you are going to use, then at night go into your back yard and switch it on ,now walk the distance tyou want to throw and measure how wide and deep it is. this is a totally foolproof method which allows for the masking effect of the can.