Biophilic design in the brain – and what it means for the lights.
Excited a growing number of studies that use the patterns of activity in the brain associated with cognitive effort or stress to complement more subjective ways of measuring preference and performance in response to lighting conditions – we’re notoriously unreliable when it comes to self-reported effects.
I’ve been fascinated to see how closely these neural correlates of visual ergonomics correspond to the statistical properties of natural scenes, codified in the principles of Biophilic design-
- Distribution of brightness (maps along a gradient that corresponds to around 50% difference between the brightest and darkest zones within a region of a scene) – A Cerebral Basis for Visual Discomfort and Visual Stress.
- Distribution and orientation of edges – horizontal and vertical lines take less effort than oblique ones, with preference for a wide range of edge orientations across a scene – a preference that kicks in at just four months old – The edge orientation entropy of natural scenes is associated with infant visual preferences and adult aesthetic judgements.
- Distribution and range of hues with a preference for the chromatic range found in natural scenes over synthetic tones as they tend to stimulate a cluster of cones rather than making one cell type do all the work. This preference starts early – at just four months old, too – Colour vision is aligned with natural scene statistics at 4 months of age. But that doesn’t mean magnolia – this article warns of dire developmental dangers of ‘beige motherhood’) – “Beige Motherhood”: Harmful to a Child’s Color Perception and Brain Development.
What does that mean for the lights?
- Screen to ambient lighting ratio – perhaps unsurprisingly, research suggest that the optimal balance is for the screen to be between 30 and 50% brighter than the surrounding area. In a dark room, that’s a glow, not a glare. Next to a window on a sunny day, that means turning the screen brightness up to ‘full’.
- Layering light sources to highlight forms and features- something as simple as the leaves of a plant – can generate the variety of edge orientation your brain needs to feel at home.
- Natural colours tend to be more comfortable, but you will only ‘see’ the colours if the light source generates the wavelengths in the first place. Blue-enhanced LEDs engineered to boost the body clock not only make colours look less natural, they make your eyes feel tired. In contrast, light sources that generate a spectrum of wavelengths closest to sunlight (‘high colour rendering index’) seem to be linked to reduced markers of stress – and may even improve reaction times in critical driving conditions – like driving into a tunnel – Effects of blue-enriched white light with same correlated colour temperature on visual fatigue.
It’s such an exciting time to be working in this field where we can lift the lid to watch the brain running the code in real time.
Now it’s our job us to create the conditions where this remarkable machine can do it’s job as smoothly and joyfully as possible.
Flicker is supposed to be bad for us, so how come 40Hz light therapy is good?
A question from Jamie, one of my wonderful and curious swimming friends as we bobbed along together last week. Oddly enough, three separate people have asked me the same question sincee. Realising I didn’t have a clear and coherent response, I thought I’d have a go at putting one togther, so here goes…
Flicker
All artificial lighting systems involve some degree of flicker (rapid changes in brightness, or temporal light modulation), simply because they are taking electricity and turning into a stream of photons. How big that light-dark difference is, the shape of that modulation and how fast that cycle takes place come together to create a calculation that is part of the technical specification – although performance in real world installations is often different – A Market Surveillance and an Evaluation Methodology Based on Power Quality, Electromagnetic Compatibility, and Photometric Data for LED Light Sources.
60 cyces per second is known as the ‘flicker fusion frequency’ – the speed at which the average person can consciously perceive these changes in brightness.
But there are measurable differences in brain activity and comfort at almost twice that speed at 100 cycles per second – Effects of Temporal Light Modulation on Cognitive Performance,Eye Movements, and Brain Function.
Although, as another review points out, frequencies up to 15kHz can trigger measurable changes in eye movements and blood flow to the eye, indicators of strain or stress – Temporal Light Modulation Activation in Visual Cortex – A 7T fMRI Study on Healthy Subjects.
40Hz light therapy
This is operating at a freqency well below that critical threshold, and seems to be engaging a different mechanism.
The brain is essentially, an electrical circuit running a number of frequencies, or speeds of oscillation. Gamma, ranging from 25 to around 100Hz, kicks in when your brain is getting stuck into complex or focused tasks that involve multiple brain regions – like binding inputs from multiple senses, retrieving and making memories. Scientists studying early changes in people living with Alzheimer’s Disease noted a distinctive alteration or degradation in those frequencies, speculating that if they could ‘put them back’, they could slow down cognitive decline.
A decade later, there is a growing body of evidence that their hypothesis was right.
Pulses of light, sound and even vibration at 40Hz (or 40 flashes or cycles per second) may indeed impact a number of key mechanisms involved in AD, from clearing amyloid plaques through the lymphatic system, reducing synaptic loss and cell death – Unleashing the potential: 40 Hz multisensory stimulation therapy for cognitive impairment. While early experiments were carried out in mice models, a growing number of small-scale protocols with human participants, like this one with a specialist LED light box engineered to deliver pulses of light at 40Hz are showing encouraging results – Study on the effect of 40 Hz non-invasive light therapy system. A protocol for a randomized, double-blinded, placebo-controlled clinical trial.
What’s so special about 40Hz?
This was identified as a ‘special’ frequency almost 40 years ago by scientists studying the visual system. They noted that cells in different parts of the retina fired at the same 40Hz cycle when stimulated by the same object, and that synchronisation seemed to be central to the conscious perception of an object as an integrated whole – or ‘binding’. This frequency has also been picked up by wellbeing and sleep apps, leveraging the association between ‘binaural beats’ and deep relaxation
Click on this website if you’d like to hear what 40Hz sounds like without the whale song 😉
And this article from MIT is a valuable guide with links if you want to learn more – Evidence that 40Hz gamma stimulation promotes brain health is expanding.
Have a great weekend!