The housing of the drying unit has two openings, through which the printed web (13) passes, moving vertically upwards. The housing incorporates a lamp unit (14) with a reflector (30) a high intensity ultra-violet light source (37) and a unit for the rotatable mounting of the lamp unit in the housing so as to move the reflector from one position where the ultra-violet radiation is directed onto the web to a second position where the beam is directed away from the web. An energy absorption chamber is joined to the lamp unit and receives the radiation whenever the reflector is in its second position. An air circulation unit directs an air stream around the reflector and the chamber and through an assembly which screens the radiating lamp from the flowing air.
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