Resonance lamp that contains mercury vapour at pressures of about $0.1\text{Pa}$ ($0.75\times {10}^{-3}\text{Torr}$; $1\text{Torr}=133.33\text{Pa}$). At $25{}^{\text{⚬}}\text{C}$, such a lamp emits mainly at $253.7$ and $184.9\text{nm}$. They are also called germicidal lamps. There are cold- and hot-cathode as well as cooled electrode-less (excited by microwaves) low-pressure mercury lamps. The Wood lamp is a low-pressure mercury arc with an added fluorescent layer that emits in the UV-A spectral region ($315$-$400\text{nm}$).