Nails by Mariette

405 nm LED nail lamps cure nail gel with UV. That is not a myth, it is a fact.
Every so-called "405 nm" LED nail lamp sold as a visible-light curing lamp actually cures with UV. Claims that they don't are false, and this applies to all of them. This is not just a pattern I have observed, it is built into the hardware: a real 405 nm LED emits across a band roughly 15 to 20 nm wide, so any lamp that peaks near 401 to 405 nm automatically emits part of its light below 400 nm, which is UV.

Nail brands are too often misled by the LED nail lamp manufacturers, the companies that actually design and build the lamps for nail product brands around the world. Some lamp manufacturers are reputable; many are not, and some misrepresent their LED nail lamps, leading nail product brands to make false claims about them.

A common tactic involves an international test method called IEC 62471. This standard assigns a photobiological safety classification (a Risk Group) based on how hazardous a lamp's wavelengths are to skin and eyes. The classification brands cite is not a measure of how much UV a lamp emits. That distinction is the heart of the problem.

IEC 62471 rates how potentially hazardous the emitted wavelengths could be to skin, not how much UV is present. Some wavelengths cause sunburn and skin damage far more readily than others. UV between 390 and 400 nm is very unlikely to cause sunburn, so a lamp emitting only these wavelengths tests at near-zero risk. Lamps that also emit 365 nm have very low risk too. The test has long been used, correctly, to show that nail lamps in general do not produce harmful levels of UV. I have relied on this test myself to demonstrate nail lamp safety, so the results are valid.

The issue is that some lamp manufacturers misrepresent a near-zero hazard rating in a way that leads some nail product companies to believe it means "no UV." Those are two very different things. The number is near zero because 400 nm light barely causes sunburn, NOT because no UV is emitted. A lamp can produce a large amount of UV between 390 and 400 nm and still be very unlikely to cause a sunburn, and still score near-zero risk.

Recently, CND advertised one such lamp, claiming it does not use UV to cure its gels. In discussions with the company, I learned the claim was based on IEC 62471 test results.
However, when I tested this same lamp with a spectroradiometer, which measures the actual light an LED nail lamp emits, I found that about 40% of its emission is UV, as the attached graph shows.

Once CND recognized the error, they quickly agreed to drop the "no-UV curing" claim, and I applaud them for that. This is how a highly responsible company should behave, and it is my hope that other companies making such claims will be courageous enough to follow their example and admit the lamps are not UV-free. Other, less responsible companies that I have shown this same error to have simply ignored the facts and continue to incorrectly call their lamps UV-free. It is this UV that activates the gel's photoinitiators and drives curing. No nail gel I am aware of cures by visible light alone. Every nail gel I have tested requires UV to cure, and I have found no exceptions.

It is wrong to think of 405 nm LEDs as visible light only. They are violet-dominant: typically, 60 to 70% violet light, with the rest UVA. Calling them "visible LEDs," as some manufacturers do, can be misleading. To my knowledge, no nail lamp on the market can properly cure gels without UV. Nor should these be referred to as visible light lamps. I suggest the correct name is violet-dominant lamps, since at least 50% of the emissions are in the violet range.

About the attached spectra: these are four scans taken inside the newest CND "Visible Light" nail lamp. They peak at 401 nm (which is visible light) and spread from there into the UV. Even with the peak in the violet range, the 40% UV portion measures 19 to 20 mW/cm² of UV irradiance. That is higher than many nail lamps on the market, which typically emit 12 to 20 mW/cm² of UV, with a few reaching 30 to 32. This is not a minuscule amount of UV, and this UV contributes substantially to the cure.

Filter the UV out of this kind of lamp and many colored gels will likely not even cure to hardness, especially darker colors. And curing to hardness is a low bar; it is often not the same as a safe, proper cure. Without lower UV wavelengths such as 365 nm, it is much more difficult to properly and safely cure many hard-to-cure colors, which was the subject of my last Facebook post. That is exactly why dual-wavelength lamps exist, to help ensure better curing of colored gels. The shorter-wavelength UVA penetrates dark, pigmented gels and drives a more complete through-cure.

Consider this a warning to all nail brands. Some lamp manufacturers may use this test method to mislead you, and not only about this. Beware! Do not be fooled. 405 nm nail lamps do NOT cure only with visible light; that claim is false. And to be clear, these lamps are safe, when used as directed, but so are lamps using 365 nm and 390 nm LEDs.

Please share this information widely. We need to work together to eliminate misinformation and improve the quality of educational information being taught about nail products and lamps.