Distance vs. Beam Angle vs. Beam Spread

Foxinabox10

Active Member
Joined
May 1, 2004
Location
Boston, MA
Does anyone know of a formula that takes the beam angle and throw distance and gives the resulting light diameter at both visible width and effective width?
 

BillESC

Well-Known Member
Joined
Aug 29, 2005
Location
Kilmarnock, VA
A handy quick referrence is the photometric data sheets for each fixture available at www.altmanltg.com

Otherwise you can do it the old fashion way by drawing a vector (at the appropiate angle) and using a 1" = 10' scale measure out both legs of the vector to the distance you need and measure between the two legs to determine beam diameter.
 

ricc0luke

Active Member
Joined
Feb 23, 2004
Location
Central Illinois
Well you want the actual trip formula here it is... but only when a light is perpendicular to the surface it is projecting on-

When the angle of the beam spread (degrees) = A,
The distance from the light to the surface (ft) = d,
And half of the beam spread in feet = x
The total beam spread in feet = 2x = s

tan(1/2*A)=(x/d)
x=(d)tan(1/2*A)

since x is only half... the formula you are looking for is...

s=(2)(d)tan(1/2*A)

I suppose if you want I could explain why you have to do all that.... just not right now, I gotta get running!
 

SketchyCroftPpl

Active Member
Joined
Dec 28, 2004
Location
Near Worcester, Mass
The day my math teacher told me about ... when trig would actually play a role in my life. Its funny though cause you end up using it so much like when we were trying to build a ramp and needed to do all the angles for it and stuff like that. We ended up not using it but it is some really good stuff to look up and know about if your going to be building stuff or doing anything.

~Nick
 

propmonkey

Well-Known Member
Joined
Jul 22, 2004
Location
Milwaukee, WI
basic trig that i learned in 8th grade is the stuff i use every week but the stuff in trig class i used on the acts and thats been about it