UVA indoors: nail lamps, tanning beds and what your lights really emit

Indoor ultraviolet is a field with one genuinely alarming source, one obvious one, several minor ones, and one persistent myth. This article sorts them, and puts each in the same units — so you can see how a gel-manicure lamp stacks up against midday sun rather than against a vague feeling.

Everything in one table

UVA irradiance in W/m², with the equivalent UVA Index reading using this site's scale (irradiance ÷ 6), so the numbers are comparable to what the calculator shows for outdoors:

The nail-lamp row is the one to read twice. At the top of its measured range, a nail lamp is putting more UVA on the back of your hands than the sun does at noon in July.

Gel-manicure lamps: the live question

Nail-curing lamps exist to drive a photoinitiator in the gel, and the photoinitiators used absorb in the UVA. So these lamps are engineered to be UVA sources — older units peak near 365 nm, newer LED units nearer 365–405 nm. Either way the output is almost entirely UVA-I, the deepest-penetrating part of the band, delivered at close range directly onto thin, frequently exposed dorsal hand skin.

What the evidence actually shows:

• Output varies wildly. A survey of 17 lamps found UVA irradiance from 0.6 to 15.7 mW/cm² — a 26-fold spread. There is no meaningful "a nail lamp emits X"; it depends entirely on the unit, and salons do not publish the figure.
• Cellular damage is demonstrated. A 2023 study in Nature Communications irradiated human and mouse cells with a standard nail-polish dryer and found substantial cell death after a single 20-minute exposure, rising sharply with repeated sessions, plus reactive-oxygen-species generation, mitochondrial and DNA damage, and mutational patterns of the kind associated with oxidative stress — which is precisely UVA's known mechanism.
• Human outcome data are thin. There are scattered case reports of squamous cell carcinoma on the dorsal hands of frequent users, and no cohort or case-control study showing elevated skin cancer rates in the gel-manicure population. Earlier risk modelling using lower-output lamps concluded the per-visit dose was small.

What to do: fingerless UV-protective gloves are the cleanest fix, since they remove the exposure entirely and do not wash off or need reapplying. Broad-spectrum sunscreen on the backs of the hands 20 minutes before the appointment is the fallback — but only with real UVA protection, because SPF alone is a UVB measure and does nothing relevant here.

Tanning beds: not ambiguous

Tanning units are the one indoor source where the science is settled. Their lamps are deliberately weighted toward UVA — UVA drives immediate pigment darkening with less burning, which lets sessions run long enough to be commercially viable. UVA irradiance in a unit runs to several times midday summer sun, and high-pressure units are reported at ten to fifteen times.

The IARC classified UV-emitting tanning devices as Group 1 carcinogens — carcinogenic to humans — in 2009, the same category as tobacco smoke and asbestos. Use before age 35 is associated with a substantially raised lifetime melanoma risk, and the risk rises with the number of sessions. Several countries have banned commercial sunbeds outright, and many others prohibit their use by minors.

There is no protective benefit to offset this. Tanning is itself a damage response, "base tans" from UVA provide a nominal SPF of around 2–3, and UVA produces no vitamin D — that is UVB's job, and UVA-shifted lamps are specifically designed to minimise it.

The blue-light myth

"Screens emit UV and you need sunscreen at your desk" is a marketing claim, not a physical one. Two facts settle it:

• Blue light is not ultraviolet. Blue light spans roughly 400–490 nm and is, by definition, visible. UVA ends at 400 nm. They are adjacent, not overlapping.
• Displays emit essentially nothing below 400 nm. LED backlights and OLED emitters are built from blue emitters and phosphors with no meaningful ultraviolet component. Measurement studies of phones, tablets and monitors find UV output indistinguishable from background.

The claim is not entirely empty, though, and it is worth knowing which part survives. High-energy visible light — particularly the violet-blue around 415 nm — genuinely does induce pigmentation, and does so most strongly in deeper skin tones and in melasma. That effect is real and clinically relevant. What does not follow is that a screen delivers a relevant dose: measured visible-light irradiance from a display is orders of magnitude below daylight, and a few minutes outdoors exceeds a full working day at a monitor. If you have melasma, the window beside your desk is the problem, not the desk.

Bulbs: small, controlled, occasionally worth knowing

• Fluorescent tubes and CFLs generate UV internally — that is how they work — and the phosphor coating converts it to visible light. Some UVA and a little UVB leak through. Regulatory testing has found single-envelope CFLs with imperfect or cracked coatings emitting enough to matter at very close range; double-envelope designs, which add an outer glass shell, essentially eliminate it. At normal room distances the exposure is negligible for almost everyone.
• Halogen lamps run a tungsten filament very hot inside quartz, and quartz transmits UV that ordinary glass would block. This is why halogen fittings are required to have a glass cover or filter. An undoped, uncovered halogen bulb used as a close-range desk or task light is the one lighting case that has produced documented skin reactions.
• LED bulbs emit no measurable UV. Replacing halogen and fluorescent fittings with LED removes this category entirely.
• Blacklights, UV curing lamps and insect traps are genuine UVA sources at 365 nm, but irradiance falls off with the square of distance and normal use keeps you far enough away.

If you are photosensitive from medication or a condition, these small sources move from "negligible" to "worth managing" — a photosensitive patient can react to a bare fluorescent tube. For everyone else, they are a rounding error against the window.

Ranking indoor UVA honestly

1. Tanning beds — a known Group 1 carcinogen. No safe use.
2. Gel-nail lamps — high, localised, variable, and trivially avoidable with gloves.
3. Sunlit windows — modest intensity, but hours a day for years, and the one most people ignore entirely.
4. Halogen and bare fluorescent at close range — small, relevant mainly to photosensitive people.
5. Screens, LED bulbs, phones — zero. Not a source.

The UVA Index on this site models sunlight outdoors and does not attempt to account for artificial sources. But the irradiance scale is the same, so the table above lets you place any of them on a number you already read.