Downlight Beam Angle Explained

When you’re installing LED downlights, the beam angle is a very important factor. It influences the way the room is illuminated, and therefore the overall visual effect of the lighting. If you have a good idea of the precise lighting effect you’re going for, you can work out exactly what beam angle you need in your bulbs, as well as the number of bulbs you need to install in the ceiling. But if you’re stuck with an existing setup, you can still use bulbs with different beam angles to achieve a lighting effect that’s more to your satisfaction. So let’s find out all about beam angles.

What is the beam angle of a light bulb?

Beam angle can perhaps be best explained with reference to the theatre. There, you’ll find all sorts of lighting that have been set up to maximise the visual and emotional effect of the performance. 

• At one end, you have spotlights. These are used to focus intense light on a particular actor, and can be used for emphasis or for projecting different colours on certain parts of the stage. A spotlight hardly flares out after leaving the lamp, so this would be described as a narrow beam angle.
• On the stage, there will probably also be a certain amount of floodlighting, which is more subtle, but covers more of the stage. A few simple floodlights in above the stage will make sure that all of the stage, actors and set are visible, albeit not necessarily brightly. These would be considered wide angle lamps.
• In between those two extremes, there’s an infinite sliding scale of beam angles. A lighting designer will be able to decide which parts of the stage require which types of lighting.

In domestic terms, you can think of a naked bulb hanging from the ceiling as an extra-wide angle light. It will have a beam of 360° in all directions, apart from a small area occupied by the bulb fitting itself. As downlights are mounted in the ceiling (or in a shielded surface mounted fitting), it’s impossible for the beam to be more than 180°, as no light can escape upwards. In practice, even 180° would be impossible to achieve as the mount itself would cause some shadow.

Choosing beam angle for a space

Downlights are usually parabolic, and set in a ceiling which means light can only escape in one direction – the back is either mirrored, or the cluster of LEDs only points downwards. The beam of light forms a cone emanating from the bulb, the angle of which is part of the bulb’s specification.

• A 45° beam would illuminate directly below it, and in a cone up to 22.5° all around.
• A 60° beam would reach to 30° all around the vertical
• A 20° beam would be more focused, spreading only 10° around from the centre line.

As you can imagine, a single downlight with a narrow beam angle, right in the middle of a room, would only illuminate a small circle underneath it. For most purposes, that would be uncomfortable and unacceptable. However, if there’s other lighting in the room, and that one light is there to illuminate a single object, such as a table or an ornament, it could be exactly what you want.

For most domestic purposes, downlights are spaced evenly around the ceiling of a room, however. This ensures uniform lighting throughout. For regular, comfortable illumination, bulbs with average beam angles (around 45°) are perfect.

However, if you are working with a high ceiling, it’s probably best to choose narrow angle bulbs. By the time the light reaches head height, it will have spread enough to cover the whole room. Conversely, if you have a low ceiling, the widest beam angle available will ensure consistent lighting throughout, without excessive shadows and hotspots.

Remember, you will never find a downlight that spreads more than about 120°, as they are always recessed into the ceiling (or the fitting) to a certain degree, so no light can escape upwards. Any illumination of the ceiling will be incidental, reflected off surfaces below.

So if you’re starting from scratch, with a lovely blank ceiling ready to be drilled, think about what effect you’d like. With a little trigonometry you can work out how the light beams will interact with each other, and design your fitting layout accordingly.

For example, you might want plenty of lights in the ceiling, but with narrow beams, or you might want as few as possible by spacing them out more. Alternatively, you might want to focus the downlights in a certain zone, in which case you can carefully work out what certain beam angles will look like, and how the light will interact with objects, floors, walls, furniture and people.

Professionals use software such as Dialux or Relux to model the shape of the room and to play with different lighting concepts. If you’re a lighting designer, they are well worth investing in.

When you’re working with an existing installation, you can still use your choice of beam angles to flood the room or focus it in smaller areas, depending on how you want the room to feel. You can even mix it up a little if you want, with both narrow and wide beams dotted around.

Beam angle versus intensity

Bulb brightness is measured in watts for consumers, but a more scientific measurement is the lumen. You’ll also see this on most bulbs’ packaging. This represents the total amount of light emitted by the bulb. Another measure is candela, which is the amount of light that lands on an object, or the amount measured at a certain point.

If you have a beam of light that doesn’t spread at all (i.e. a laser), the candelas will essentially be the same as the lumens. But as soon as any beam angle is introduced, the intensity will start to drop for every metre the light travels. The wider the beam, the more those lumens are shared over a larger area, and the candelas will get smaller and smaller the further it travels.

So if you want wide angles but lots of illumination, you should choose higher lumens (or wattages) in your LEDs.

If you have narrow beams with high lumens, the light might be very intense when it hits a surface, in which case you might prefer to opt for a less intense source. Again, this should all factor into your choice of bulbs, whether you’re designing from scratch or working with an existing arrangement of fittings.

If you’re not sure about intensity, you can always opt for dimmable bulbs with a dimmer switch. That way, you can tailor the intensity to your needs at any given moment.

Now you’re fully illuminated on the ins and outs of beam angles, why not start shopping for high quality LED bulbs?