Sunlight is part of everyday life. How it affects you depends on the type of light, the amount of exposure, and your skin. Understanding these differences is where your Sun Score begins.
Shorter UV
280–315 nm
UVB contributes to sunburn and skin damage. It also plays a role in vitamin D production in the skin.
Longer UV
315–400 nm
UVA contributes to skin aging and can also damage skin. Understanding exposure means looking beyond whether you develop a sunburn.
Light we can see
400–700 nm
Light reaching the eyes helps regulate the body’s daily rhythm, a different pathway from UV exposure on skin.
You cannot manage what you cannot separate. The90 reads UVA and UVB independently, in real time, on Live UVA and UVB meters.
The number you already have
The UV Index is a regional forecast. Your skin lives somewhere more specific. It was built to warn a whole region about sunburn [9]. It misses three things.
Your surroundings. It cannot see your car window, reflective concrete or water, shade, or snow.
UVA. Weighted toward sunburn, it underreads the rays that age you.
You. Your skin type, history, and sunscreen never enter the math.
Personal UVI
A live reading of what is actually reaching you, measured from your skin and tuned to your profile. Your weather, not the weather.
The upside is real
The benefits are peer-reviewed, not folklore. As we age, and the body’s natural production and repair start to slow, these move from background health to something worth managing.
Vitamin D. We make a majority of our vitamin D from the sun, and researchers like Dr Weller suggest it is better than supplementation when available. Many adults run low, and skin makes less with age, so measuring it becomes increasingly important.
Bones. That vitamin D drives the calcium absorption behind bone density, which declines for everyone from your late 20s on.
Mood. Serotonin rises with hours of bright light and falls in winter. One of the few free daily levers.
Sleep. Morning light sets the clock behind sleep, which erodes with age.
Heart, emerging. Sun on skin releases nitric oxide, which lowers blood pressure, and more sun tracks with lower cardiovascular mortality. Heart disease is the leading cause of death for both men and women.
Skin. The right dose keeps skin healthy, the wrong dose ages it. Up to an estimated 90% of visible aging is linked to UV.
A supplement copies one output. Sunlight is the whole system, vitamin D, nitric oxide and circadian light at once. The only catch was the risk, which is exactly the problem The90 solves.
Every benefit has a threshold
Past a point, the same sun starts to cost you. The problem was never the sun. It was the dose, and it compounds with age.
UVB overexposure. The burning rays, linked to sunburn and long-term damage.
UVA overexposure. The deep, silent rays behind most visible aging.
Sun Debt. The UVA still on your skin from recent days. You feel a burn. You never feel this.
The app measures both in real time and carries your Sun Debt forward, so the invisible becomes something you can act on.
Sun Score
The90 Sun Score
Everything above, balanced into one number, daily. A balance score from 0 to 100, what you collected against what it cost, tuned to your skin. Understand how you did at a glance, track trends over time, and dig into the details when it matters.
Collect
Vitamin D, circadian light, nitric oxide (emerging)
Cost
UVB overexposure, UVA overexposure, Sun Debt
Every claim on this page traces back to published research. Numbers match the references in each section.
01
Vitamin D: a D-lightful solution for health
Holick MF · Journal of Investigative Medicine · 2011
02
Sunlight and vitamin D for bone health
Holick MF · American Journal of Clinical Nutrition · 2004
03
Effect of sunlight and season on serotonin turnover in the brain
Lambert GW, et al. · The Lancet · 2002
04
Impact of windows and daylight exposure on sleep quality of office workers
Boubekri M, et al. · Journal of Clinical Sleep Medicine · 2014
05
UVA irradiation of human skin lowers blood pressure
Liu D, Weller RB, et al. · Journal of Investigative Dermatology · 2014
06
Avoidance of sun exposure as a risk factor for major causes of death
Lindqvist PG, et al. · Journal of Internal Medicine · 2016
07
Sunscreen and prevention of skin aging: a randomized trial
Hughes MCB, et al. · Annals of Internal Medicine · 2013
08
Effect of the sun on visible clinical signs of aging in Caucasian skin
Flament F, et al. · Clinical, Cosmetic and Investigational Dermatology · 2013
09
Share of visible aging linked to UV, UVA’s penetration of glass and cloud, and UV Index background
Skin Cancer Foundation · World Health Organization · Global Solar UV Index
10
Rise in cardiovascular risk with age, and heart disease as the leading cause of death for men and women
American Heart Association · CDC
Is there a subscription or monthly fee?
No. Your Gem comes with the full The90 app and every core feature, with no monthly fee to read your own light. You buy the sensor once.
What does The Gem actually measure?
It reads the UVA and UVB reaching your skin, separately and in real time, then turns the day into a single Sun Score from 0 to 100. Along the way it tracks the light you want, like your morning circadian light and your estimated vitamin D, and the exposure you want to manage, like the UVA that ages your skin.
Do I have to wear it as a necklace?
It comes as a jewelry-grade pendant on a matching gold or silver chain, so you can wear it out of the box. The Gem is also a removable core, so it can move into new ways to wear it as they launch, including a hat clip and bag tag on the way.
How is this different from the UV Index or my weather app?
The UV Index gives one number for a whole city and says the same thing to everyone. The Gem measures the light actually hitting your skin, separates the aging rays from the higher-energy ones, and reads it against your personal skin profile in real time. It is the difference between a forecast and your actual day
Can I wear it in the water?
Rain, sweat, and a quick rinse are all fine. The Gem is water resistant to 1 meter for 30 minutes, so leave it off for the pool, the shower, hot tubs, and saunas.
What if it is not for me?
Try it for 30 days. If it is not right, send it back for a full refund, and every Gem is covered by a 1-year warranty. Free shipping, dispatched from California within 1 to 2 business days, currently within the US.
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