The science of light
Light is the strongest signal your body clock has. Bright light in the morning tells it the day has begun, and gentler light in the evening lets it wind down. Here is what the research says, and how Halo puts it to work with daylight-white light for mornings and 660nm red light for evenings.
The winter blues
On the shortest day, London gets less than half the daylight of midsummer, and much of it arrives while most of us are indoors. Fewer bright mornings means a weaker signal to your body clock.
Using a bright light to stand in for daylight, often called light therapy, is something many people turn to in the darker months, and researchers have studied it for winter low mood since the 1980s. Halo brings that bright morning light into a wearable, so you are not tied to a box on the table.
Daylight in London
How bright is bright?
Typical, rounded values on a log scale. Light levels vary with weather, distance and direction.
Your body clock
Every cell in your body follows a roughly 24-hour rhythm, kept in time by a master clock in your brain. Its main messenger at night is melatonin, the hormone that makes you feel sleepy.
Melatonin stays low through the day, rises in the late evening and peaks in the early hours. Light is what keeps that rhythm on time: bright light in the morning switches it off, while bright light late in the evening can push it back.
*Gooley et al. 2011: 116 healthy adults. Compared with dim light, ordinary room light before bed delayed the rise of melatonin in 99% of people and shortened its night-time release by around 90 minutes. Curves are illustrative.
What morning light does
Five steps, from morning light reaching your eyes to a body clock that is set for the day. Tap any step.
Halo's light bar sits at your brow and shines bright light towards your eyes. It passes through the cornea and lens and lands on the retina at the back of the eye.
A small set of cells in the retina contain melanopsin, a light-sensitive pigment that responds most to blue-green light. They are not there for seeing. Their job is telling your body what time it is.
These cells send their signal to the suprachiasmatic nucleus (SCN), a tiny region deep in the brain that acts as your body’s master clock.
In the morning, the master clock tells the pineal gland to stop releasing melatonin, the hormone that makes you feel sleepy, so you feel more awake and alert.
Bright light at a similar time each morning helps keep your body clock on time, so sleepiness builds again at the right time in the evening.
Two kinds of light
The cells that set your body clock do not see colour the way you do. They respond most to blue-green light, and barely at all to deep red. That is why Halo uses two different lights.
In the morning, you want the signal. Halo’s daylight-white light is bright and broad, including the blue-green wavelengths these cells respond to, so your body clock gets a clear message that the day has started.
In the evening, you want light without the signal. Halo’s red light sits at 660nm, far from the 446 to 477nm range that is most potent at holding back melatonin. It gives you a warm light to read or relax by as your body gets ready for sleep.
Sensitivity curve drawn from Brainard et al. 2001, who found 446 to 477nm the most potent at suppressing melatonin (627 tests, 72 volunteers). Illustrative.
Meet Halo
Halo combines daylight-white light for your mornings with 660nm red light for your evenings, in a lightweight frame you can wear while you get on with your day.
Bright, broad white light for your mornings, close to your eyes and completely hands-free.
A warm, gentle light for your evenings, far from the blue-green light that tells your body it is daytime.
Have breakfast, answer emails or get ready. Halo works while you do.
Designed for everyday wear, and it sits comfortably over most prescription glasses.
Why Halo
Two simple sessions a day, built around what you already do.
15minutes of daylight-white light
Wear Halo while you get ready, have breakfast or check your emails, and give your body clock a clear start to the day.
660nm warm red light
Switch to red as the evening draws in and let your body get ready for sleep.
2sessions a day, morning and evening
A steady morning signal helps keep your body clock on time, so evenings feel easier to wind down.
7h 49mof daylight in London on the shortest day
When the days are short, Halo brings bright light to your morning, whatever the weather.
Read, work or have breakfast while Halo does its thing. Your routine stays exactly as it is.
How it compares
A traditional light box sits on a table and asks you to sit in front of it. Halo puts the light at your eyes and lets you move, with a second, red light for your evenings.
| Feature | Halo | Traditional light box |
|---|---|---|
| Hands-free and wearable | Yes | No |
| Use it while you work, read or get ready | Yes | Limited |
| Bright white light for mornings | Yes | Yes |
| Red light mode for evenings | Yes | No |
| Light close to your eyes | Yes | Sits on a table |
| Portable | Yes | Limited |
The evidence
Light therapy was first described for winter depression, known as seasonal affective disorder (SAD), in 1984.
Since then, researchers have published thousands of papers on how light shapes our sleep, our mood and the body clock that runs them.
Source: PubMed searches, October 2026.
What the evidence says
Summaries of the studies behind this page, on light, mood, melatonin and sleep. Each links to the study on PubMed.
Seasonal affective disorder
A review of randomised controlled trials found that bright light treatment significantly reduced the symptoms of seasonal affective disorder.
Golden et al. American Journal of Psychiatry, 2005Healthy adults
Ordinary room light before bed delayed the evening rise of melatonin in 99% of people and shortened its night-time release by around 90 minutes, compared with dim light.
Gooley et al. Journal of Clinical Endocrinology and Metabolism, 2011Healthy adults
Light between 446 and 477nm, blue-green, was the most potent at suppressing melatonin, pointing to a dedicated light sensor for the body clock.
Brainard et al. Journal of Neuroscience, 2001Elite athletes
30 minutes of red light each night for 14 days improved sleep quality and melatonin levels compared with a group who had no light.
Zhao et al. Journal of Athletic Training, 2012The studies use different light sources, brightness, timings and people. They did not test Halo itself, but help explain the science behind morning and evening light.
Halo
Halo brings daylight-white light to your mornings and 660nm red light to your evenings, hands-free.
£199.99
Dispatch from 26 October
FAQ
Need help choosing? Our UK team is happy to talk it through.
Get in touchHalo is a wellness product. It is not intended to diagnose, treat, cure or prevent any disease, including seasonal affective disorder. If you are struggling with low mood, speak to your GP.
To ensure the best fit of your Pulsio Compression Boots, measure the inseam of your leg from your heel to
the uppermost part of your inner thigh.
If you are in between sizes, we recommend sizing down to ensure the best fit.
| Size | Upper Thigh | Leg Inseam | Height |
|---|---|---|---|
| Small |
Up to 27” Up to 69cm |
25” - 29” 64cm - 74cm |
5’0” - 5’5” 152cm - 168cm |
| Regular |
Up to 29” Up to 74cm |
29” - 34” 74cm - 86cm |
5’5” - 6’0” 176cm - 182cm |
| Large |
Up to 32.5” Up to 83cm |
34” - 36” 86cm - 91cm |
6’0” - 6’6” 182cm - 198cm |
To ensure the best fit of your Pulsio Compression Boots, measure the inseam of your leg from your heel to
the uppermost part of your inner thigh.
If you are in between sizes, we recommend sizing down to ensure the best fit.
| Size | Upper Thigh | Leg Inseam | Height |
|---|---|---|---|
| Small |
Up to 27” Up to 69cm |
25” - 29” 64cm - 74cm |
5’0” - 5’5” 152cm - 168cm |
| Regular |
Up to 29” Up to 74cm |
29” - 34” 74cm - 86cm |
5’5” - 6’0” 176cm - 182cm |
| Large |
Up to 32.5” Up to 83cm |
34” - 36” 86cm - 91cm |
6’0” - 6’6” 182cm - 198cm |
