[References for the operating behavior of ultraviolet fluorescence tubes in phototherapy equipment]

The working behaviour of the UV-fluorescent tubes type UVS 20-2, UVS 40-2 and UVS 65-2 (Manufacturer: VEB NARVA "Rosa Luxemburg" Leuchten- und Leuchtstoff-lampenwerk Brand-Erbisdorf) applicated in phototherapy equipments has been investigated in four commercially and two self-made devices. In the first 100 hours of the application of the fluorescent tubes an exponential decrease of the irradiation power reaching a value of 30 percent must be considered. After an exchange of old tubes (1,500 working hours) to new one a jump in the irradiation power with a factor 2.5 may be observed. The temperature of the fluorescent tube altering after the switch and daily instabilities in the supply power influence the irradiation power in a way that must not be neglected. The emission of equipments with good remove of the tube heat is constant after 5 minutes. In constructions causing and maintaining a high temperature of the tubes this time is about 20 minutes.