Robin Barton


Beam Calculator

The tools on this page allow you to calculate various characteristics of a beam of light depending on what you already know. The terms used are:

Beam Angle (θ)The optical dispersion of the light beam - the angle at which the light spreads. This is often shown on the lens tube (e.g. 26°) and, in the case of zoom profiles is a range (e.g. 18° - 32°).
Beam Diameter (O)The diameter of the beam of light at the throw distance from the source.
Throw (T)The distance between the front of the luminaire and the surface being lit. It is the measurement you would get if you put a tape measure from the centre of the lense down the centre of the beam to the surface being lit.

Basic Calculations

This section assumes that the beam of light hits a surface staight on, i.e. the beam is circular not elliptical. For other instances, see the "Advanced Calculations" setcion below;

I know the beam angle and throw:    I know the beam diameter and throw:
Beam Angle (θ) °Beam Diameter (O) m
Throw (T) mThrow (T) m
Beam Diameter (O) mBeam Angle (θ) °

Please read the disclaimer.

Advanced Calculations

This section is for instances when the beam of light does not hit the illuinated surface straight on, which is the most common situation. In order to perform these calculations we use some additional terms:

Beam Depth (Y)The depth of the beam - i.e. the distance between the nearest and furthest points from the source.
Beam Width (X)The width of the beam.
Focus Angle (f)The tilt angle (degrees). This is measured from vertical, i.e. 0° is the source pointing directly downwards and 90° means that the source is horizontal.
Source Distance (D)The (horizontal) distance from the centre of the lens to the centre of the beam (focus point).
Source Height (H)The (vertical) height of the centre of the lens.

Beam Angle (θ) °  Throw (T) m
Source Distance (D) mFocus Angle (f) °
Source Height (H) mBeam Depth (Y) m
  Beam Width (X) m

Please read the disclaimer.