Get the good out of the sun. Own your light.

★★★★★ 4.8 from early-access wearers. Developed in collaboration with Dr. Richard Weller, world-renowned UV expert.

Smart UV Sensor

Buy Now - $299

The sun has powerful health benefits, and it also carries real risk. Own the most misunderstood input to human health.

Explore the health benefits of sunlight, UV light, and vitamin D, and the science behind them.

Vitamin D

Sunlight on skin is how your body makes most of its vitamin D.

See the science →

Nitric oxide

Emerging research links sun on skin to nitric oxide and healthy blood pressure.

See the science →

Mood

Morning light supports serotonin and a lighter, steadier mood.

See the science →

Sleep

Morning light sets the internal clock that helps you sleep at night.

See the science →

Bones

The vitamin D you make in the sun supports the calcium absorption behind bone strength.

See the science →

Cardiovascular

Emerging research ties regular, balanced sun to cardiovascular health.

See the science →

Skin

The right dose keeps skin healthy while limiting the UVA that ages it.

See the science →

Vitamin D

Sunlight on skin is how your body makes most of its vitamin D.

See the science →

Nitric oxide

Emerging research links sun on skin to nitric oxide and healthy blood pressure.

See the science →

Mood

Morning light supports serotonin and a lighter, steadier mood.

See the science →

Sleep

Morning light sets the internal clock that helps you sleep at night.

See the science →

Bones

The vitamin D you make in the sun supports the calcium absorption behind bone strength.

See the science →

Cardiovascular

Emerging research ties regular, balanced sun to cardiovascular health.

See the science →

Skin

The right dose keeps skin healthy while limiting the UVA that ages it.

See the science →

Vitamin D

Sunlight on skin is how your body makes most of its vitamin D.

See the science →

Nitric oxide

Emerging research links sun on skin to nitric oxide and healthy blood pressure.

See the science →

Mood

Morning light supports serotonin and a lighter, steadier mood.

See the science →

Sleep

Morning light sets the internal clock that helps you sleep at night.

See the science →

Bones

The vitamin D you make in the sun supports the calcium absorption behind bone strength.

See the science →

Cardiovascular

Emerging research ties regular, balanced sun to cardiovascular health.

See the science →

Skin

The right dose keeps skin healthy while limiting the UVA that ages it.

See the science →

The90 is a personal sun intelligence system: a jewelry-grade sensor and a connected app that measure the UV your skin actually receives and turn it into one number you can act on.

Get the highlights.

A jewelry-grade UV sensor that lifts out and moves with you.

The Sun Score balances the benefit and the risk of your day in the sun. Aim for The90.

Your live light dashboard: real-time UV, your exposure, your benefits, your trends.

Vitamin D, morning light, mood and sleep, skin protection and an emerging heart-health signal.

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A jewelry-grade UV sensor that lifts out and moves with you.

The Sun Score balances the benefit and the risk of your day in the sun. Aim for The90.

Your live light dashboard: real-time UV, your exposure, your benefits, your trends.

Vitamin D, morning light, mood and sleep, skin protection and an emerging heart-health signal.

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The90 Gem · UV Sensor

Meet your personal sunlight guide

The90 Gem is a photonic UV sensor small enough to wear as jewelry. It reads UVA and UVB separately, all day, wherever you are — no forecast, no guessing.

Advanced UV sensor

Reads UVA and UVB, separately. A photonic UV sensor captures the rays that matter, not just the generic UV index you get from your regional weather forecast.

Modular design

The Gem is designed to be worn multiple ways. It clicks into the pendant and necklace today, with a hat clip, bag tag, and more on the way.

Jewelry finishes

Available in gold or silver, with a concave face that shrugs off scratches. It layers with the jewelry you already own, so it never feels like a gadget.

Water resistant

Handles rain, sweat, and a rinse. Water resistant to 1 meter for 30 minutes. Skip the pool, shower, hot tubs, and saunas.

1 week battery life

A week on a charge. Seven-plus days of everyday wear on a single charge. Charges full in under 2 hours.

Free companion app

No subscription. Every core feature comes with your Gem. There is no monthly fee to use the app.

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Advanced UV sensor

Reads UVA and UVB, separately. A photonic UV sensor captures the rays that matter, not just the generic UV index you get from your regional weather forecast.

Modular design

The Gem is designed to be worn multiple ways. It clicks into the pendant and necklace today, with a hat clip, bag tag, and more on the way.

Jewelry finishes

Available in gold or silver, with a concave face that shrugs off scratches. It layers with the jewelry you already own, so it never feels like a gadget.

Water resistant

Handles rain, sweat, and a rinse. Water resistant to 1 meter for 30 minutes. Skip the pool, shower, hot tubs, and saunas.

1 week battery life

A week on a charge. Seven-plus days of everyday wear on a single charge. Charges full in under 2 hours.

Free companion app

No subscription. Every core feature comes with your Gem. There is no monthly fee to use the app.

Slide 1 of 6

Sun Score

A score you can't win by hiding, or by burning

Most wearable scores reward more. Sun doesn't work that way. Too little and you miss the benefits, too much and you take the damage. A Sun Score means you got both right.

Learn more

The90 Companion App

Your very own light dashboard

Your sunlight benefits, at a glance. Vitamin D, circadian light, and emerging heart-health signals, tracked from the light you actually receive.

Vitamin D. Your estimated daily benefit, tracked toward a healthy target and then capped, so you know when you have enough.

Nitric oxide. Stored in your skin and linked to lower blood pressure. Sunlight on your skin unlocks it.

Your circadian window. The morning and evening light that sets your energy, mood, and sleep, tracked so you catch the good light at the right time.

History and trends. A daily recap paired with how your skin actually felt, turning a single glance into a trend line you can act on.

Your skin profile. Type, genetics, habits, and sensitivities. The UV Index speaks to everyone. Your Score speaks only to you.

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Vitamin D. Your estimated daily benefit, tracked toward a healthy target and then capped, so you know when you have enough.

Nitric oxide. Stored in your skin and linked to lower blood pressure. Sunlight on your skin unlocks it.

Your circadian window. The morning and evening light that sets your energy, mood, and sleep, tracked so you catch the good light at the right time.

History and trends. A daily recap paired with how your skin actually felt, turning a single glance into a trend line you can act on.

Your skin profile. Type, genetics, habits, and sensitivities. The UV Index speaks to everyone. Your Score speaks only to you.

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Your skin's UV load, live. Sun exposure, sun debt, and sessions, tracked as they land.

Personal UVI. A live reading of what's actually landing on you, through the car window, under the umbrella, in the shade.

UVB exposure. We measure the UVB reaching your skin, the rays linked to sunburn and long-term skin damage, in real time so it never adds up unseen.

UVA exposure. We measure the UVA that ages your skin, the deep rays you never feel, tracked as it silently accumulates through the day and across the weeks.

Sun debt. The UVA still on your skin from the last few days. You feel a burn. You never feel this, until the app says ease off.

Sun Session. Your day in the sun, plotted minute by minute. You see exactly where the dose came from.

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Personal UVI. A live reading of what's actually landing on you, through the car window, under the umbrella, in the shade.

UVB exposure. We measure the UVB reaching your skin, the rays linked to sunburn and long-term skin damage, in real time so it never adds up unseen.

UVA exposure. We measure the UVA that ages your skin, the deep rays you never feel, tracked as it silently accumulates through the day and across the weeks.

Sun debt. The UVA still on your skin from the last few days. You feel a burn. You never feel this, until the app says ease off.

Sun Session. Your day in the sun, plotted minute by minute. You see exactly where the dose came from.

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What early adopters are saying

★★★★★ 4.8 · Based on 486 early-access reviews

★★★★★

“Once you start wearing this necklace and geeking on the data, you won’t want to take it off”

Rebecca Burns

★★★★★

“It looks like jewelry, not a gadget. My friends ask about the pendant before they ask about the tech.”

Sofia L. · Early access reviewer

★★★★★

“The reapply alerts alone are worth it. I burn less and I’m outside more than ever.”

Jenna K. · Early access reviewer

Frequently asked questions.

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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2026

Own your light