resonance lamp that contains mercury vapour at pressures of about 0.1 Pa (0.75 x 10E-3 Torr; 1 Torr = 133.33 Pa). At 25°C, such a lamp emits mainly at 253.7 and 184.9 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 nm).