While there has been much focus, deservedly, on “Human Centric Lighting” health and wellbeing is a topic with far broader aspects in lighting. We need to remain mindful of how all other aspect of light can impact our wellbeing.
Light has potent physical impacts on us that are not related to our eyes or visual system. We are all aware of our natural requirement for daylight and sunlight to allow us to synthesise Vitamin D in our skin. This is essential to maintain healthy calcium levels and bone structure. Equally, excess sun exposure causes sunburn that can result in skin cancers. These actions are both caused by exposure to UVb radiation. UV can also cause corneal opacity and cataracts. Our current light sources, blue pumped phosphor converted LEDs do not emit any of this part of the spectrum. However legacy light sources such as mercury discharge based fluorescent, metal halide and even the humble tungsten halogen lamp can emit dangerous levels of UV particularly in poorly designed or damaged fittings. We need to watch out in the future as UV is being used in laser LED pumped light sources currently being developed here in China. We are also using even more potent UVc integrating this with lighting equipment for sanitization of spaces, this has to be done with extreme care to avoid accidental human exposure to the UVc.
When discussing wellbeing we must not forget psychological impacts of lighting. My introduction to this field was through stage lighting where light is used specifically to manipulate the audience, giving cues for time of day, for mood or emotion and even to manipulate change in the audience’s feelings about a character. Most of these are subliminal, unconscious effects. Lighting can do the same thing in architecture by accident or design. We are all aware of our own mood changes when we have a dark overcast sky compared to a bright sunny day. Why is it so common to enter spaces such as shops or offices where we have a uniform, comparatively low level of cool even light as experienced on a cloudy day? Why even do we even value lighting uniformity as a design goal?
Our entire evolution, developed from outdoor living as hunter gatherers and in agrarian societies right up to the early 19th Century. Given that we have changed to a predominantly indoor industrial society only in the past two centuries we have to consider that our physical beings have not significantly moved on in our relationship with light. We still visually function as a species intended to live predominantly outdoors, in daylight during the day and indoors, or at least protected beside an open fire, at night. These conditions of relatively bright high colour temperature light in the day while we work and low brightness warm, incandescent light at night when we relax, and sleep are our natural condition.
The mechanism in the body that reflects this has only relatively recently been discovered. Research into the third receptor in the eye, the Intrinsically Photosensitive Retinal Ganglion Cell (iPRGC) its connections in the brain to non-image processing areas and the consequent effects of melanopic lighting has coincided with the development of the LED, which has an easily manipulated Spectral Power Distribution and an ease, if not necessity, to be controlled electronically. Now just because something is easy to do does not mean that it should always be done. We have leapt into this idea that changing the colour appearance and intensity of light over the course of the day will always be beneficial. My thinking on this is that in many if not most architectural applications we may only be creating a theatrical effect and any apparent impacts are merely psychological. Frankly there has not been sufficient research yet, particularly in real, live workplaces, to see what the effects of varying colour temperature and intensity are, and how applicable building them into our design process is. I am aware of one current piece of research in this field based on the work of the Manchester group published last year in PLOS and I look forward to seeing the results of this study late this year.
One thing, though, I am bound to say, is that our current metrics for light, and our general design targets and methods are of absolutely no use in measuring or optimising the melanopic effects of light. Our core method of quantifying light the Lumen remains bound to the V lamda curve. This is based on lab experiments on a few students in 1931, 1951 and sort of again in 2018 it relates only to the Photopic visual response to daylight like light levels. Under most artificial lighting our eyes are not responding to this curve, rather the Mesopic curve defined in 1951. The iPRGC response is different again to the visual response and far to the blue end of the spectrum compared to the photopic curve.
We continue to design standards based on task area illuminance levels. These are of questionable relevance as they eye does not see the light delivered, only that reflected from the task or surface. Given the massive increases in recommendations for task lighting in the past 70 years, it is a reasonable assumption, that our visual system has not evolved significantly to our indoor artificially lit environment over this period, and now the majority of our tasks particularly in the office environment, are now self-illuminating screens, this continued focus on task illuminance seems to be highly questionable. Task illuminance is pretty much irrelevant to iPRGC response and therefore any melanopic effects on the human body. Light needs to be measured at, or as close as possible to the retina, at least in the vertical at eye level and with consideration of the iPRGC spectral response to determine what impact it has on the various melanopic responses.
So far, we have only discussed normal, average and healthy responses to light and lighting. Unfortunately none of us are “average” and if “normal” is the typical 20s to 30s male student who are the predominant subjects for lighting research experiments few of us fall into that category either! Some things we think we know about, like the reduced sensitivity of the eye as we age. As the owner of a pair of conventionally “ageing” eyes I am told I need significantly more light to perform normal tasks. I will accept that I am not “average” however I don’t need more light, what I need is higher contrast in the tasks I am performing. I am also much more bothered by the loss of focusing accommodation, varifocal glasses not withstanding!
While I maintain my previous statement on evolution, we are seeing changes in humans. These are caused by changes in morphology (body form) created by changes of diet, medical intervention, exercise regimes and lifestyles in general. These are likely to account for the larger number of glasses wearers, and the greater number of people who have restricted vision who in previous decades would have been functionally blind. This ever-increasing population also need to be considered in our design thinking. We need to be aware of and understand the needs of this population. Their needs differ depending on their specific visual problems. A long time ago I had a client with Retinitis Pigmentosa, often characterised as tunnel vision. This degenerative condition results in ANY light source in the subject’s field of view causing totally disabling glare. Understanding this was essential to developing the project for him, as it happened a very theatrical, dynamic landscape lighting scheme. This was a very major learning exercise and has informed my design thinking and the questions I ask about users of the spaces I am designing for.
This includes neurodivergent, neurodegenerative, hypersensitive and other neurological differences which affect sensory processing and mental wellbeing. We can recognise some clear diagnoses wher lighting has known impacts that are included in this group, Attention Deficit, Hyperactivity Disorder, Autism, Migraine, Epilepsy, Parkinson’s Dementia and many others. There are also many people who have hypersensitivity to lighting without specific diagnosis. We need to be mindful of people with these challenges and consider their needs in our design work. British Standards published PAS 6463:2022Design for the mind – Neurodiversity and the Built Environment which is freely downloadable and while not exhaustive at least provides some guidance with these issues.
Another aspect of lighting that is also increasingly problematic is flicker. We used to be comfortable that we could not see flicker above around 400Hz. This applied for older light sources such as incandescent or fluorescent and even high intensity discharge where there was a degree of persistence of light output. In an LED world we find that flicker and stroboscopic effects like the phantom array visible when your eye scans across a car’s taillight are in fact visible at frequencies up to 10 kHz. As switch mode power supplies that chop up electricity to control current are almost universal, we need to think whether we have another factor that could make lighting cause discomfort or worse.
As lighting designers, we need to be keenly aware of all the impacts of light on the users of the spaces and places we design. We need to keep up with both research and technological developments to make sure that we are at least doing no harm. However, we can also use our almost magical powers of illusion to create engaging, uplifting, and spiritual spaces with light.
Kevan Shaw 15 June 2023