The beam angle is the measurement for how the light is distributed and how large of an area it illuminates.   It is the angle at which the light spreads outward from the source it is coming from.  It is measured in degrees and will often have three classifications: narrow, spot or flood.   

Choosing the correct beam angle will help to ensure that the light output meets the desired effect that you are looking for.   

The Technical Definition

In technical terms a beam angle is defined as the angle between the two opposing directions at which the luminous intensity is 50% of the maximum intensity, typically measured at the centre of the beam. This 50% threshold is widely recognized as the standard for determining the effective spread of the light.  Light outside of this primary beam angle is referred to as spill light. 

Classifications of Beam Angles

Beam angles are typically grouped into the below categories:

A light fitting with a narrow beam angle will concentrate the light into a small area making it ideal for highlighting specific objects, architectural features and artwork. A fixture with a wide beam angle will spread the light over a larger area which is preferable for ambient lighting.  This sort of lighting is commonly used in general everyday spaces.

What Beam Angle should I choose?

1. Accent or Task Lighting (e.g., highlighting artwork, reading): A narrow to medium beam angle (15° to 35°) is recommended as this concentrates the light and draws attention to one specific point with highly focused illumination.
2. General Downlighting (such as standard ceiling lights in a hallway or kitchen): A medium beam angle (35° to 60°) is recommended for this as it provides a good balance between focused lighting and still has a sufficient spread for comfortable lighting without excessive shadows.
3. Ambient or Area Lighting (such as large living rooms, offices, retail floors): A wide beam angle (60° to 120° or more) is recommended as this gives a wide beam of light and will distribute the light softly and evenly to create shadow-free illumination.

The height of the ceiling or mounting location of the light should also be taken into account when choosing a beam angle.  This is because the higher you need to put the light the more likely you will need to have a narrower beam to make sure the light reaches the full surface area below. 

Understanding Specific Beam Angles

1. A 40 degree beam angle falls into the medium spot to flood range.  It is a light that is moderately focused and produces a medium beam of light.  It can be used in a wide variety of applications and is often used for residential and commercial environments.  
2. A 120 degree beam angle is considered to be a wide flood angle of light.  It has a very wide light distribution and will spread light even over a large area.  This is often used in panel lights and in areas that have a large interior such as a garage or parking lot.
3. A 36 degree beam angle is considered to be in the medium spot light beam angle range.  It is a focused light designed to deliver a high intensity light to a particular point or area.  It is a popular choice for use in retail and gallery settings.