The power of light to change your world for good
Light Notes banner

Vive la difference!

Nobody is average. As we get better at measuring response to light, we are starting to see just how different we all are. So this week, I’ve put together some papers you might enjoy.


Eyes change with age

Babies’ eyes are a ‘work in progress.’

• They grow by over 65% before they stabilise in adolescence. Like a plant, when those growing eyes don’t get enough light they grow long and weak. The pandemic saw a tripling in myopia cases because children didn’t get outside enough. Classroom design and taking break times outside can cut risk and severity of myopia by up to 40% – Protective effects of increased outdoor time against myopia: a review , Prevalence of macular complications related to myopia – Results of a multicenter evaluation of myopic patients in eye clinics in France.

•  The wiring between eye and brain and their hand-eye co-ordination are under construction too. Mouse models show that low-stimulus environments lead to significant gaps in functional ability in later life – Circuitry Underlying Experience-Dependent Plasticity in the Mouse Visual SystemSo limit the time they spend staring at a flat screen and give their eyes a variety of shapes and patterns to explore.

•  The non-visual system is forming too: not only are their eyes tens of times clearer than an adults so their eyes receive more light, but their hormone cycles are more pronounced too. A teen’s body clock is up to twice as sensitive to evening light exposure than an adults: just 40 lux, the light from a tablet, is enough to keep the average adolescent brain wide awake – Lighting in the Home and Health: A Systematic ReviewSo make sure they have a soft warm light in their room and encourage them to switch to music, a podcast – or an old-fashioned book – in the hour before bed.

•  As we get older, our eyes grow cloudy, reducing the amount of light, including the sky blue wavelengths that help to set the body clock.  Recent work suggests that the red cones come into play to boost the signals to the non-visual system – S-cone contribution to the acute melatonin suppression response in humansSo lighting that delivers a broad spectrum of wavelengths (or has a high Colour Rendering Index or CRI) is even more important than we thought.

•  As we age, the lenses grow stiff and we struggle to focus on the details. But it seems as though our ability to see the wood for the trees  – a mechanism known as we global topographical perception – remains roughly the same – Age-related changes in local and global visual perception.


Men are from mars – or the blue planet?

This study found that men may see the world in a different light, noting a two-fold difference in the stimulus response curve to the blue part of the spectrum in men compared to women.

This neural response was mirrored in subjective perception: men perceived cool light as significantly brighter than warmer light, while women didn’t see the difference.

This may explain the difference preferences for cool over warm light preference between the genders: Men preferred cool light over warm (62.5% v 37.5%), while women were the opposite (12% for the cool v. 87.5% for the warm).

The same study found that disturbance at night affects women’s cognitive function significantly more than men.  Women’s performance also varied l over the course of the day, with the biggest impact in the early hours of the morning – Sex differences in the circadian regulation of sleep and waking cognition in humans.

Men are more likely to be colour blind than women – around 1 in 12 men and only one in 200 women, with a small number of women who have an extra ‘green’ colour-sensing cone. The Colour Blindness Awareness Charity has some great advice here.

There seem to be differences in the way that genders cross-check visual information with inputs from other senses. This study tested that principle by serving hungry participants an omelette for breakfast under normal and blue light. The food looked unappetising and the men ate less, while the women trusted their sense of smell and tucked in anyway – Blue lighting decreases the amount of food consumed in men, but not in women



Why do some cultures seem to prefer bright, cool lights in their shops and restaurants while others prefer a dim, cosy feeling?  This may be linked to the light levels where you grew up: people from hotter climates with higher light levels tend to prefer bright light indoors too – The whiteness of lighting and colour preference, Part 2: A meta-analysis of psychophysical data.

That heritage is also likely to affect the colour of your skin and eyes as you will be adapted for higher light levels for non-visual response including Vitamin D production. Darker skin protects against skin damage from the sun. But you also need more light to synthesise Vitamin D and trigger a cascade of non-visual responses too – Seeing the light to change colour: An evolutionary perspective on the role of melanopsin in neuroendocrine circuits regulating light-mediated skin pigmentationThe Protective Role of Melanin Against UV Damage in Human SkinColour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes.

But as we travel the world, whether you are an individualist or feel more at home fitting in may be a better indicator of whether you prefer cool or warm light than your culture or where you were born – Intercultural observer preference for perceived illumination chromaticity for different coloured object scenes.


Finally, just a couple of places left for two events at the Tridonic Showroom at Light23 on Tuesday and Wednesday next week.  

On Tuesday at 3:30pm, John Bullock and I will be sharing the work we’re doing in a Residential Care Home, including luminaire design and controls. Register here

On Wednesday at 3pm, John will be in conversation with Simon Fisher of F-Mark and Simon Blazey of Tridonic about wireless controls for retrofit and remanufacturing, Register here.

Get in touch!