Light on the brain

Dr Shelley James

Notes from Light Tribe Webinar with Phos, 28 May 2020

We’re all familiar with the way that plants lean towards the light – and we tend to think of that leaning to the light as a metaphor. But turns out that this response is more than a figure of speech.

The plant hormone auxin and the receptor TIR1 triggers ‘stretch’ or lengthening of cells on the side of the plant that is away from the light to create that ‘bend’ . It’s fascinating to learn that a similar enzyme / protein bond in humans may well be involved in cancer and other conditions such as Parkinson’s - and new treatments are being developed to harness that light-response mechanism.

The ability to orient ourselves in space, to identify mates and seek out predators (and hide from them!) is so vital to life on earth that the ability to ‘see’ evolved over 550 million years ago

The evolution of this remarkable organ that we call an eye started off as a with single light-sensitive spot, gradually becoming a dip or depression with a smaller aperture like a pinhole camera – able to focus light – then transparent layer to cover the front / keep it clean, rinsed by salty water through a sponge of trabecular meshwork and tear ducts. There are creatures with every stage of evolution living today.

One of the simplest structures on earth is called an Erythropsidinium. This single-celled organism has no ‘brain’ at all - and yet has an eye that occupies up to 1/3 of its body that actually ‘swivels' eye to target its prey.

Nuts and bolts of sight…

Before we talk about how light affects brain and behaviour, it’s probably worth a quick review of the process itself. Our experience of seeing – and that’s the same for all living things from plants to primates - is combination of external phenomena and internal processing.

Out in the world, a stream of photons falls on and then is absorbed by or bounces off a surface in space. The ‘hardware’ of vision – eyes, nerves, synaptic connections gather those signals and pass them on to be interpreted by the ‘software’ of vision.

The brain can process some kinds of information within as little as 13 milliseconds.

That’s the pathway that triggers the ‘duck’ reflex when a tennis ball is flying towards you. It takes a lot longer for that information to be processed into awareness of a ‘thing’ or a ‘place. So you could say that we are ‘seeing’ things that have already happened!

In terms of our discussion of the role of light in directing behaviour, we will focus on two linked but parallel pathways.

The first is the Image-forming pathway – specialist structures called rods and cones that line the back of the eye. These are sensitive to different wavelengths of light and respond rapidly to changes in the pattern of distribution entering the hole in the front of the eye. This is the system that gives us information about things and spaces in the world - safe of not, sexy or not, edible or not…

The second, discovered relatively recently by Prof Russell Foster, is a parallel system of specialist ganglion cells – called intrinsically photosensitive retinal ganglion cells or IPRGC because they contain a light-sensitive pigment called melanopsin. These detect slow changes in the brightness and warmth (or ‘colour temperature’) that signal different times of day. This sets off a train of physiological reactions that get us ready to do the things we need to do at that time of day – be alert for hunting and hiding, slow down to rest and recover…

These are the two key qualities of light to consider when we bring light into our spaces so that we can be happy, healthy and productive.

These systems are constantly evolving in response to expectation, adaptation, training and ageing - hardware changes with age, software changes with expectation- garbage in, sense out.

Living in a box…

Richard Gregory describes this as the ‘black box’ theory of perception. Our brains are, quite literally, in the dark. We build hypotheses about what is out there in the world and only around 30% of what we ‘see’ is fresh information


Light and behaviour

When we’re looking at designing a space, there are two broad dimensions to consider: The position of the light source and the quality of that light source. People tend to turn right when entering a space and will even climb over barriers in their efforts to 'swim upstream'. But placing a bright light in the left hand corridor creates a significant shift in that pattern.

Position of the light…

The position of the light source is a vital cue to where that object is located in space – and our relationship with it.

So for example, light on a face from below gives a strange ‘otherworldly’ feeling – because we expect light to be coming from above. Equally, light coming from the side casts deep shadows and suggests mystery. Light from above confers a sense of superiority, light from directly in front tends to give a sense of confidence.

Images by Amaury Descours –

The position and the optics or ‘focus’ of the light also makes a massive difference to our experience of a space and our position in it. For example, glare or dazzle from a focused light source in the line of vision creates a sense of vulnerability and tension, a uniform spread of light from a diffuse source creates a sense of being in a public space and discourages intimate conversations. Non-uniform lighting creates intimacy. Complex lighting is perceived as pleasant, while a combination of overhead & edge lighting creates an experience of spaciousnes,

It makes sense really, if you relate those different states to lighting conditions out in the wild. Essentially, we behave ‘better’ when we are in bright daylight. We exhibit more pro-social behaviour, make healthier choices about what to eat and how much, and stop when we are on a losing streak –

Take a risk…

Casinos know this very well. Compulsive gamblers don’t stop after a loss – they don’t even slow down. It turns out that red lights inhibit that ‘slow down you’re onto a loser’ reflex. When you add gambling sounds, that reflex is even weaker. You don’t stand a chance!


Retail designers know this too -

As a general rule, customers associate ambient with low cost and accent with upmarket. Some stores – TKMaxx, Boots, Lidl – are ambient only, while some – Abercrombie & Fitch, Hollister, SuperDry – are accent only, to great effect.

Customers pick up twice as many items from shelving with integrated lighting, than those with none - and once it's in your hands, you are far more likely to take it to the till. And when you are there, if the cash register is bathed in a warm golden light, you are likely to be more generous and patient.

Savvy retail lighting designers adjust the colour temperature to appeal to different age groups: A cool colour temperature (4000K to 6000K) conveys spaciousness and appeals to a young demographic while warm colour temperatures (2700K to 3000K) convey familiarity and appeal to older, upmarket customers.

The colour of the light also affects the way produce looks – a supermarket chain in Germany changed their lighting to a circadian system with dramatic impact on the value and volume of sales, customer loyalty and staff retention.

Lighting also shapes our perception of value of a whole range of things- including houses – ‘curb appeal’ external lighting can increase the perceived value of a house by 20%...


Once you get the food home, the lighting conditions affect what you eat and how much.

One study, published in The Journal of Marketing Research looked at the orders of 160 diners at four chain restaurants. Half the diners were seated in dimly-lit rooms, and half were seated in well-lit areas. The diners who were sitting in low light ordered 39% more calories. Meanwhile the people in brighter surroundings were 16% to 24% more likely to choose healthy menu items (think grilled fish or white meat and veggies). In follow-up experiments, the researchers got the same results from hundreds of college-aged students.

Author Dr Dipyan Biswas explained why - we feel more alert in brighter rooms and therefore tend to make more healthful, forward-thinking decisions,"

In fact, the researchers found that when diners in dimly-lit rooms were given a coffee placebo (or simply asked to be more alert) they were just as likely as their peers in the well-lit rooms to make healthy food choices.

It seems making healthy choices has more to do with the brightness of your mental state than the brightness of the room. So don't swear off candle-lit dinners yet. The best way to avoid overindulging is to make yourself feel more alert, said co-author Brian Wansink, PhD, the director of the Cornell Food and Brand Lab.

That could mean going for a brisk walk before dinner, or splashing some water on your face for an instant energy boost. Pick-me-ups like these might actually be preferable, because as Wansink pointed out, mood lighting isn't all bad. In prior research, his lab has found that people who eat in darkened rooms enjoy their food more, eat slower, and consume less overall.

And at work…

Lighting makes a shockingly big difference to our productivity - even more important as many of us work from home.

Just look at the difference between the wavelengths given out by different light sources. Given how sensitive our bodies and brains are to subtle shifts in the orientation and optics, brightness and composition of light, it’s not surprising that this has a massive impact on our ability to think straight and stay focused

Lux levels –

One study found that when horizontal luminance was alternated per work shift (between 800 and 1200 lux) the speed of workers in a factory assembling electronic devices increased significantly in the 1200 lux condition.

The colour of the light, as well as the brightness, makes a big difference to how well we perform too – not surprising given how deeply that connection with the cycle of day and night is embedded in our brains.

For example, Blue-enriched white light (17000K) improved the subjective measures of alertness, positive mood, fatigue, performance, irritability, concentration and eye discomfort. They also found that daytime sleepiness was reduced, and the quality of subjective nocturnal sleep was improved.

Age makes a big difference too. Younger women were affected (both positively and negatively). for longer than the males. Older adults showed a negative mood in cool bluish lighting, whilst younger adults showed a more negative mood in warm, reddish light (Knez & Kers, 2000). Children approaching their teens (8-12 years old) were more positively inclined towards a reddish light that made them feel calmer. This study also showed an increase in pro-social behaviour, better reading comprehension by the participating students, as well as greater reading speed and fewer errors.

Health care

There are two key dimensions to consider here. Not only functional qualities – being able to see clearly for tasks like dispensing and surgery. But also physical changes related to circadian entrainment that alter the way drugs are absorbed.

There is now growing evidence that vitamin D levels are a key indicator for mortality from Covid-19. countries with higher rate of Vitamin D deficiency have experienced higher infection rates – paradoxically, Italy has a high vitamin D deficiency. 68 per million in the UK on the 3rd of April to 2 per million in Australia on the 10th of April. The body synthesises Vitamin D from skin exposure to UV wavelengths (280 to 315 nanometres). Just sitting by the window is not enough because the glass cuts those out.

For example, the average stay for patients suffering from bipolar disorder was 3.67 days shorter for bipolar patients with East-facing windows. Patients staying on the bright side of the hospital unit were exposed to 46% higher-intensity sunlight on average. This study found that patients exposed to an increased intensity of sunlight experienced less perceived stress, marginally less pain, took 22% less analgesic medication per hour, and had 21% less pain medication costs (Walch et al., 2005).

In another study, 41 preterm infants in structurally identical critical-care units were provided either cycled or noncycled lighting (constant light levels during the day and night) during a lengthy hospital stay. Compared to infants in the noncycled lighting condition, infants assigned to the cycled lighting condition had a greater rate of weight gain, were able to be fed orally sooner, spent fewer days on the ventilator and on phototherapy, and displayed enhanced motor coordination (Miller et al., 1995).

Back to nature…

And back to those plants and animals– they are all affected by light as we are – and light pollution can be as damaging as plastics and emissions.

Light spilling from our 24 hour cities disorients and disrupts the migration, nesting and feeding patterns of sea creatures like turtles and the everyday birds and insects that are so vital to food production as well as to our wellbeing.

Implications / conclusions

A growing body of research is demonstrating the power of light to harm or to heal. Not only ourselves but every single life form under the sun. A revolution in lighting technologies, optics and controls are making it possible to harness this force for good. More important than ever in a 24/7 lock-down world.

It really is up to every single one of us to see the light.

References and further reading.

  1. GREGORY, RICHARD L.Eye and Brain: The Psychology of Seeing - Fifth Edition. REV - Revised, 5 ed., Princeton University Press, 1997.JSTOR, Accessed 28 May 2020.




















  21. accessed 22/5/2020