For all practical purposes, no — there are no meaningful UV rays at night. Once the sun has fully set and the sky has darkened to true night, the UV index drops to zero. You cannot tan, burn, or experience any UV-related skin effects from being outside in the dark.

The slightly more nuanced answer involves twilight — the period between sunset and true night. During the early part of twilight, some UV does still reach the Earth’s surface through atmospheric scattering. But this fades quickly and is gone completely by the time the sky is fully dark. As for the moon being a UV source, it does reflect tiny amounts of UV — but at levels so far below any biological threshold that it has no effect on skin whatsoever.

Key Takeaways

At true night, UV index = 0. There is no meaningful UV radiation reaching the Earth’s surface once the sky is fully dark.
During twilight — the period between sunset and true night — some UV is still present through atmospheric scattering, but it drops very rapidly as the sun drops further below the horizon.
The three phases of twilight (civil, nautical, and astronomical) each have progressively less UV. By astronomical twilight, UV is negligible.
The moon reflects a tiny fraction of the sun’s UV back to Earth, but this is millions of times weaker than daytime UV — far below any level that could affect the skin.
You cannot tan or burn at night from natural sources.
Artificial UV sources — black lights, UV sterilisation lamps, certain stage lighting — do emit UV and can affect the skin, but these are manmade, not natural night UV.
The original claim that UV is “reflected by the ozone layer” at night is incorrect. The ozone layer absorbs UV — it doesn’t reflect it. The mechanism for twilight UV is atmospheric scattering.

Why UV Disappears at Night

UV radiation reaching Earth’s surface comes almost entirely from the sun. During the day, sunlight travels through the atmosphere and UV wavelengths that survive the filtering of ozone and other atmospheric gases reach the surface. The strength of this UV depends on the angle of the sun — the higher the sun in the sky, the shorter its path through the atmosphere, and the more UV arrives at the surface.

As the sun sets, its angle flattens and its path through the atmosphere lengthens dramatically. UV wavelengths are increasingly absorbed and scattered before they can reach the surface. By the time the sun is at the horizon, UV is already very low. Once the sun has dropped well below the horizon, the path length through the atmosphere becomes so long that essentially all UV is absorbed or scattered before it reaches ground level. UV index reaches zero.

The ozone layer plays a key role here — it absorbs UV radiation, particularly UVB. This is a common point of confusion: the original version of this article described UV being “reflected by the ozone layer.” That’s not accurate. The ozone layer absorbs UV rather than reflecting it, which is why it is so effective as a natural protection mechanism. Without the ozone layer, far more UV would reach the surface throughout the day — which is also why ozone depletion has been a significant environmental concern for skin cancer rates.

What Happens During Twilight — Civil, Nautical, and Astronomical

Twilight isn’t just one thing — it’s a gradual transition that happens in three distinct phases, each defined by how far the sun has dropped below the horizon.

Civil twilight (sun 0°–6° below the horizon) is the period immediately after sunset when the sky is still bright enough to see clearly without artificial light. The sun continues to illuminate the upper atmosphere, which scatters some light — including some UV — down to the surface. UV levels during early civil twilight are low but not negligible, particularly for UVA. If you’re outdoors for extended periods during this window in summer, particularly near the equator, some UV exposure is still occurring. The UV index at civil twilight is generally between 0 and 1 — very low, but technically above zero near the start.

Nautical twilight (sun 6°–12° below the horizon) brings a noticeably darker sky. Only general outlines of objects are visible. UV levels at this stage have dropped to the point where they are negligible for any practical skin safety purpose. The UV index is effectively 0.

Astronomical twilight (sun 12°–18° below the horizon) is the final stage before true night. The sky is almost fully dark and stars are clearly visible. Any residual UV from scattered sunlight is far below any threshold that affects the skin. UV index is 0.

True night begins when the sun is more than 18° below the horizon. At this point there is no meaningful scattered sunlight reaching the surface at all. UV index is 0. This is the standard used by the Skin Cancer Foundation, which notes that a UV index of 0 corresponds to conditions “used only at night.”

Is Moonlight a Source of UV?

This is a frequently asked question, and the answer is: yes technically, but no practically.

The moon reflects sunlight, and the solar spectrum includes UV wavelengths. So technically some UV is reflected from the moon toward Earth. But the practical significance of this is essentially zero, for two reasons.

First, the moon is a very poor reflector. Its rocky surface has a reflectivity (albedo) of only around 12% for visible light — and its UV reflectance is even lower than that. The lunar surface preferentially absorbs UV wavelengths, making it a worse UV mirror than it is a visible-light mirror.

Second, even that tiny fraction of reflected UV is then further attenuated by Earth’s atmosphere before reaching the surface. The final UV irradiance from moonlight reaching Earth’s surface is estimated at roughly a million times weaker than daytime solar UV. A full moon on a clear night delivers less UV to your skin than you’d receive from a single lamp in a room. No sunscreen, no protective measures — nothing — is needed for moonlight exposure. It cannot cause tanning, burning, or any skin damage whatsoever.

The moon is a source of reflected visible light, not a meaningful UV source.

What UV Index Is at Night?

The UV index is a standardised international scale used to measure how much UV is reaching the surface at a given place and time. It runs from 0 upward, with 0 indicating essentially zero UV radiation. Weather services and apps report a UV index of 0 throughout the night, because UV from the sun simply is not reaching the surface.

To put this in context: a UV index of 1–2 is considered “low” and represents minimal risk even without sunscreen. A UV index of 3 is “moderate” and the point at which most dermatologists recommend sun protection. At night, even the UV index of 1 isn’t reached — you’re at 0. There is nothing for sunscreen to protect you from.

The UV index starts rising again before sunrise, during the morning twilight period, and reaches its daily peak at solar noon. For more detail on how the UV index varies through the day and what levels are most relevant for tanning, see our guide to what UV index is best for tanning.

Can You Tan or Burn at Night?

No — not from natural sources. Tanning from UV requires a UV index above zero, sustained over enough time to trigger melanin production. At night, the UV index is 0. No matter how long you stay outside in the dark, your skin will not tan and cannot burn from natural UV.

During early civil twilight — the window right around sunset — there is technically a very small amount of UV. But it would take an impractically long period of exposure at that minimal intensity to produce any tanning or burning effect. For everyday purposes, tanning from the sun ends at or before sunset. The best time to tan outside is well before sunset, when UV is meaningful.

Artificial UV Sources That Operate at Night

While natural UV disappears at night, there are artificial UV sources that people may encounter in the evening or at night:

Black lights (UV-A lamps) are commonly used in nightclubs, entertainment venues, and for fluorescent effects. They emit UVA radiation and can cause a small amount of tanning or skin damage with prolonged close exposure — though the intensities are generally low for casual use.

UV sterilisation lamps used in some medical, laboratory, or food-service settings emit UVC — the most energetically damaging form of UV. These should never be used around people with exposed skin or eyes, and they are not relevant to casual nighttime outdoor exposure.

Tanning beds, obviously, operate whenever a salon is open and emit significant UV regardless of time of day. The time of day you use a tanning bed is irrelevant to the UV dose — what matters is session length and bed level.

None of these are “UV at night” in the natural sense. They are engineered UV sources that happen to be used in the evening — a completely different situation from sunlight and moonlight.

FAQ

Are there UV rays at night?

Not in any meaningful sense. The UV index is 0 at true night, meaning no UV radiation from the sun is reaching the Earth’s surface. During early twilight immediately after sunset, very small amounts of UV persist through atmospheric scattering, but these drop to zero well before the sky is fully dark. The moon reflects some UV but at levels millions of times below any threshold that affects the skin.

What time do UV rays stop?

UV levels fall sharply at and around sunset and reach effectively zero during astronomical twilight (when the sun is more than 12° below the horizon). This is typically 30 to 60 minutes after sunset, depending on the time of year and latitude. For practical sun protection purposes, UV is negligible once the sky is visibly darkening after sunset, and completely gone by true night.

Are there UV rays after sunset?

Yes, briefly — during civil twilight (the period when the sky is still bright after sunset), some UV reaches the surface through atmospheric scattering from the still-lit upper atmosphere. However, levels drop very rapidly and are far below what would be needed to cause tanning or burning in any reasonable exposure window. By the time the sky is meaningfully dark, UV is effectively gone.

Is the moon a UV light?

No. The moon itself produces no light — it only reflects sunlight. It does reflect a tiny amount of UV along with visible light, but the UV reaching Earth from the moon is millions of times weaker than daytime solar UV. There is no biological effect from lunar UV — you cannot tan or burn under moonlight, and no skin protection is needed for outdoor nighttime exposure.

Why is there no UV at night?

Because UV comes from the sun, and at night the sun is below the horizon. Once the sun has dropped far enough below the horizon, its light can no longer reach the Earth’s surface through the atmosphere — the path length through the air becomes so long that all UV is absorbed or scattered before arriving at the surface. The ozone layer, which absorbs UV, plays a central role in this filtration during both day and night.

Can you get vitamin D at night?

No — vitamin D production requires UVB radiation hitting the skin, which only happens when the sun is above the horizon at sufficient elevation. At night, UVB is absent. If you’re concerned about vitamin D levels during winter or in low-sunlight climates, dietary sources and supplements are the reliable alternative to sun exposure. This is true in the daytime too — vitamin D production from the sun is limited to the hours when UV index is meaningful, typically mid-morning to mid-afternoon.

Conclusion

UV rays effectively disappear at night. The UV index is 0 once the sky is fully dark, and has been since before the sky reached that point. You cannot tan, burn, or experience any meaningful UV effect from being outdoors at night — moonlight included.

The only nuance is during twilight, particularly early civil twilight immediately after sunset, when some UV persists through atmospheric scattering at very low levels. But this window is brief and the UV is so minimal that it has no practical relevance for tanning or sun protection.

For everything you need to know about when UV is meaningful during the day, and how to time outdoor tanning sessions safely, see our guides on the best time to tan outside and how to prevent tanning.