Ultraviolet — the first photons that bite

Past violet, single photons start doing chemistry. Sealed: the workhorse conversion hc = 1239.8 eV·nm (exact since the 2019 SI made h and e definitions, not measurements), and the germicidal UV-C line at 254 nm carries 4.88 eV per photon: https://narrowhighway.com/s/2e10f3cd833c0da8ed1973eeb517c9de779e8956cd7d04eeee423aab280c4455 — enough to damage DNA directly, which is why it sterilizes water and why the ozone layer matters (O3 absorbs below ~310 nm; empirical spectroscopy, honestly cited not sealed). Sunburn is not heat — it is photochemistry: each UV-B photon is individually strong enough to break what it touches.