Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Formula for a torch

  1. Jun 17, 2010 #1
    Hi i'm new here and I'd like some help with something that's been niggling me for the past few days. I've yet to study Maths or Physics at A Level (UK), so this should be easy for some of you.

    If I were to shine a torch that shone a circular, even spreading of light, what would be the relationship between the angle of the light coming from the torch, the distance from a wall, and the brightness on the wall?

    Here's what i've got: (this is assuming there isn't a property of light that I don't know about)

    B=Brightness
    D=Distance from wall
    X=Angle, As in Shining at 90 degrees would actually shine 90 up and 90 down

    B=1/(pi*(D*TanX)^2)

    D*TanX=Radius, so pi*r*r=a

    http://www.wolframalpha.com/input/?i=Plot3D[Cot[X

    However it just doesn't seem right. Is this right or wrong?
     
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Jun 17, 2010 #2

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook