Erythema after irradiation with ultraviolet B from Philips TL12 and TL01 tubes

A trial was conducted to investigate whether the experimentally found erythema caused by irradiation from Philips TL12 (TL12) and Philips TL01 (TL01) tubes corresponded to the expected erythema efficacy calculated from the CIE erythema action spectrum. Using the CIE erythema action spectrum and the emission spectra of the two tubes, the ratio between the calculated erythema efficacy of the two tubes is TL12:TL01 = 1:4.2. Seventeen volunteers were irradiated on previously unexposed buttocks with TL12 and TL01 in doses ranging from 0.8 to 3.3 kJ/m2 and from 3.1 to 18.6 kJ/m2 respectively. The erythema was evaluated clinically and measured by skin reflectance before and 24 h after exposure. Also the pigmentation of the skin was measured before exposure. The erythema efficacy ratio between TL12 and TL01 was found to be 1:2.8. This indicates that TL01 is more or TL12 is less potent than should be expected from the CIE erythema action spectrum and that this should be taken into account when changing from TL12 to TL01 in therapy.