Non-visual Aspects of Lighting

Light has a huge aspect on our daily functioning environment enabling us to see our world in order to interact with it. Light also has an often overlooked impact on our behaviour due to ‘non-visual’ effects. Light exerts these non-visual effects as a regulator of our physiology, hormonal, and behavioural systems and serves to drive our 24-hour sleep wake cycle known as the ‘circadian rhythm’. To keep this rhythm in sync we process light information through ‘melanopsin-containing intrinsically photosensitive retinal ganglion cells’ (ipRGCs) and other non-visual pathways located in the eye. Traditional lighting metrics are good at describing how much light we need to be able to see something but less good at predicting the non -visual response to light.

Credits: Which LED light

Credits: Which LED light

So what kind of behavioural responses are driven by light? In short, nearly everything! From levels of cortisol, hunger hormones, and body temperature light really does impact every aspect of our daily physiology and behaviour. This variety of physiological responses means researchers are looking at both the clinical implications of lighting from a healthcare perspective for disease states such as depression, cancer, and acne.

More practically we can consider the way we design a lighting environment at home or in work will impact on the quality of life of the users of that space. In order to get a deeper understanding of what this means from a lighting design perspective we spoke with Peter Raynham, course director for Light and Lighting, at University College London.

Peter indicated it is currently unclear whether lighting designers should seek to maximise or minimise the non-visual effects of lighting, though the non-visual response is set to become the ‘third factor’ in lighting design. Traditionally we have measured light levels using measures like Lux however it is becoming increasingly evident these measures fail to consider the qualitative behavioural non-visual impact of illumination. This becomes a more important consideration as a new wave of lighting technology, driven by LED, penetrates the market. Light has clear behavioural effects in the lab, we can’t consider light as a drug but it does have a clear stimulus response effect.

Peter states the problem we have right now is because this research is in its infancy we really don’t know what the longer-term effects of a sea change in lighting technology are. At what dose is supplemental illumination beneficial and when could it be toxic? There are animal studies however there are significant physiological differences between species meaning the results are unlikely to translate to humans. Even within a single species of animal there are high levels of individual differences in brain structure meaning the response to the same ‘dose’ of light can vary highly. Further complications enter the picture when we consider the brains response to light can change as cells age. In short the human biological response of light is at best a world of ‘known unknowns’.

So what do we do here? Peter states the ‘daylight’ community could be more proactive in this respect, even on a gloomy day natural light can output a couple of thousand lux, and in the absence of a better measure this should not be overlooked. Peter posits “The most desirable office space is always within six metres of a window, people enjoy being driven by light”.  However we don’t live in an ideal world. Access to natural light is not always possible; shift work, deep cores, and factories are all examples of environments where natural light could be impossibility.

The lighting community have been quick to embrace the idea of avoiding ‘over-luminance’ especially as energy efficiency is pushed as a key marketing message for LED lighting uptake. Further more Peter also indicates we need to consider the way new lighting technology operates. LED lighting is directional; we have traditionally been exposed to non-directional incandescent light. With this in mind it’s important to look at how we can use LED technology with some photo-biological sensitivity. Recent lighting design trends, such as using LED strip tape to wash a wall with light, may be able to marry more efficient technology with photo-biological safety until more is known about the field.

We put it to Peter that perhaps a double blind controlled trial is the way to go. However because there are so many complex factors interplaying here studies looking at lighting and behavioural responses will give noisy error prone data at best. This means realistically epidemiological studies over longer periods of time are the only feasible way to get a deep understanding of the longer terms effects of a change in the way we illuminate our lives.

So what to do with a lack of clear best practice? Peter is recommending to his students to keep an eye on the research and take on that we do know the general direction things are moving in. Light towards the blue end of the spectrum is associated neurochemical correlates of starting the day characterised behaviourally by activity and alertness. The red end of the spectrum towards has been physiologically linked to the days-end and helps the body wind down. We should also seek to in make the most of natural light and minimising the direct impact of light on the eye. This leaves aspiring lighting designers who are concerned with non-visual responses to light with several factors to play with in order to create a pleasant environment whether it is in an office environment or a deep core.


whichledlightWhich LED light is starting an energy efficiency revolution by changing one light bulb at a time. We are the leading source of impartial reviews, consumer education, and advice for LED lighting. With literally thousands of LED products on the market varying in quality and price http://www.whichLEDlight.com is the leading independent comparison service to help users find the right LED for their home or business. All products listed at which LED light have independent lab testing to check the manufacturer specification claims match real life performance.

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