There should be no problem with uv emissions from a light unit after the
power is switched off. It only takes a few milliseconds for the u.v.
emission to stop.
With 'black light' tubes like those used in public places (discos) there is
no problem even with long exposures. Their emissions are only just into the
ultraviolet.
Mercury discharge lamps (plate burners) and carbon arcs are a different
matter entirely. They emit substantial amounts of short wavelength uv which
is harmful to both skin and eyes.
If possible short wavelength lights should be designed with a cutout so that
they can't be operated without a cover over them. (I got rather sore eyes
using a carbon arc light and don't recommend it |( )
Keith.
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Keith Dowsett "Variables won't; constants aren't."
E-mail: kdowsett@rpms.ac.uk
WWW: http://kd.rpms.ac.uk/index.html