A little equation help...

[express]

Hey Guys!
I just need a little help here. I'm trying to find the diameter of a 9 degree light at 12 feet. I keep getting 111 feet?? I happen to know that can't be right!

Thanks for the help already,
Ben

 

[seanandkate]

Image Size, Throw Distance & Beam Angle Calculator | Enlightened Lighting Ltd

About 2'.

 

[65535]

Download a copy of BeamWright here. Downloads
It's free and multiplatform.

 

[Footer]

Sounds like a homework assignment to me... Can't help ya here.

 

[chausman]

Is the decimal in the right place?

 

[derekleffew]

... I'm trying to find the diameter of a 9 degree light at 12 feet. I keep getting 111 feet?? I happen to know that can't be right!. ...

Is 9° the beam angle or field angle? What is the make and model number of the fixture (as I don't know of any 9° fixture, maybe a moving light; but in any case the field angle will always be larger than the beam angle)?

From Mathematical Formulas for Lighting - ControlBooth :
Beam diameter = distance * (2 * tan (beam angle in degrees / 2)) [This is the math upon which the calculator in the link of post #2 is based.]
Simply substitute 12 for distance, and 9 for beam angle in degrees, and solve the equation.

 

[kicknargel]

And don't forget, you could always figure it out pretty closely with a protractor, scale rule, and pencil. (Now get off my lawn!)

 

[waynehoskins]

I used a variation on that equation just the other day. It's simple trigonometry.

 

[FACTplayers]

Make sure your calculator is in degrees and not radians!

 

[express]

Well, thanks for the help. After I went back and did it again, I was getting the same answer that the webpage was getting!

Anyway incase you were wondering what it is..
Products » LED Pinspot

I'm doing a quick little job for a friend who owns a returant here in town. He's got 4 Blackhawks flags hanging on a wall, and wants only the indian head lit. Two feet in diameter would be perfect. The easiest hang position is just under 12 feet away.

Thanks again, and go hawks!