Light spill: what it is, why it happens, and what you need to know

Even if you don’t have an in-depth understanding of lighting design, there’s a strong chance that you may have heard the term “light spill” used before. Light pollution – which has implications on everything from wildlife to human wellbeing – is a significant issue when it comes to artificial lighting, and light spill is a major contributor to that overarching problem.

Light spill also has the attention of many governments around the world. In the UK, for instance, The Clean Neighbourhoods and Environment Act 2005 updated the existing Environmental Protection Act to classify light spill as a statutory nuisance. As a result, local councils in the UK have the ability to investigate light spill complaints and levy financial penalties against those who fail to comply with abatement notices.

Clearly, light spill is a critical issue to understand, and one to be taken seriously. In this post, we walk you through some of the key questions and considerations around light spill, and how you can minimise the likelihood of it manifesting through your own lighting system.

What is light spill, and why is it a problem?

Light spill refers to any light that goes beyond the area that is meant to be illuminated. When a lighting system is being designed, one of the main priorities is to ensure that the light produced is focused purely on the target area. Any light that sits outside of that is classified as “light spill”. 

Take a football stadium, for instance; when creating a specification for that space, the lighting designer will be aiming to focus all of the light produced by the floodlights onto the pitch. Should any light fall into the stands, or beyond them, that would constitute an issue of light spill. Even light directed up into the sky qualifies as light spill.

Light spill is a problem for a variety of reasons:

•  When light leaks beyond the intended boundary, the target area inevitably receives less light than was originally intended. That means that the overall effectiveness of the system is undermined, because “useful” light falls in areas where it is not needed
  
  
•   Light that falls outside of the target area also equates to wasted energy. A lighting system with light spill problems means that the owner is essentially paying to light an area that doesn’t need to be. Moreover, power is being unnecessarily wasted in the process, which raises additional issues around carbon emissions.
  
  
•  Light spill can have a detrimental impact on the surrounding environment. In the case of the example above, light directed beyond the pitch could affect the experience of supporters in the stands. In more extreme cases, it could serve as a nuisance to the local community, endanger wildlife, or contribute to the wider problem of “skyglow” – overly bright nighttime skies.
  
  

Why does light spill occur?

While light spill can be a complex issue, the simplest answer to what causes it is that light emitting from a source – i.e. a floodlight – either hasn’t been controlled effectively, or is being directed to the wrong place. There are a number of possible reasons for this. 

• Poor positioning and angling: light spill often occurs because floodlights haven’t been aimed correctly. This can be due to an issue with the overall design of the lighting solution, or because the luminaires haven’t been angled appropriately during setup.
  
  
• Missing control mechanisms: shields and shutters are attachable devices that help to direct the flow of light to an area. By shaping the beam emitted by a luminaire, they help to minimise the chances of light spill. When these devices aren’t used, the risk of light spill is much greater.
  
  
• Inappropriate fixture choice: selecting the wrong luminaires can also heighten the danger of light spill. Oversized and high-intensity fixtures can generate too broad a beam of light, one that is harder to control and more likely to spread into the surrounding area.
  
  
• Weather and wear: even if luminaires have been positioned and angled correctly, environmental factors like wind and vibrations can cause them to shift, increasing the risk of light spill. Any damage to the shields will also undermine their effectiveness.
  
  
• Optic issues: optics help to shape the spread of light from a luminaire. Badly designed or poorly manufactured optics can cause light to be misdirected, which ultimately contributes to light spill.

How do I prevent light spill?

A professionally designed, well-thought-out floodlighting system should always plan for – and manage – the issues outlined above. With that in mind, the main step to take in order to prevent light spill is to work with a partner that has extensive experience of lighting design. At Midstream, for instance, we offer a complimentary design service that includes detailed light spill drawings.

Naturally, the main preventative measures that can be taken against light spill tackle some of the issues discussed above.

• Luminaires should always be positioned and angled in a way that eliminates the risk of light spill.
  
  
• Shields and shutters should be used in order to keep light directed where it is needed. These devices should be regularly cleaned and inspected.
  
  
• The most appropriate fixtures should always be chosen, with high-quality optics that keep light focused on the target area.

Is there a difference between LEDs and older lighting systems when it comes to light spill?

Yes. Older lighting technologies are omnidirectional, which means that they emit light in 360 degrees. In the case of a metal-halide floodlight, for instance, a large percentage of the light produced needs to be reflected and redirected back to the target area. Not only is this inefficient, it is also much harder to control, increasing the risk of light spill.

LEDs, on the other hand, are fully directional. A standard LED floodlight emits light at just 180 degrees, which can then be further shaped and directed by shields and shutters.

Is light spill the same as light intrusion and light trespass?
Yes. These terms are just different names for the same issue. Any kind of unwanted light qualifies as light spill.

Is light spill the same as glare?

No, though the two are closely linked. Light spill can cause glare, with the contrast between brightly and dimly lit areas resulting in intense, uncontrolled light. Glare has implications for everything from visibility through to eye comfort, so it is important to eliminate it wherever possible. Managing light spill effectively aids with this.

If you have any other questions regarding light spill, we’d be very happy to answer them direct. Please just get in touch.