Halogen lamps and filtering

In Instance 10:65, James Whitelaw asks about the relative UV
emission of halogen and standard incandescent lamps.  Halogen lamps
emit proportionately more UV, i) because the filament operates at a
higher temperature, and ii) because the quartz bulb of the halogen
lamp is more transparent to UV than the glass bulb of a standard
incandescent lamp.  Also, higher wattage lamps emit proportionately
more UV than lower wattage ones.

Halogen lamps differ considerably in specification (filter/no
filter, beam angle etc) although they all look very similar.  Check
carefully to make sure that you get what you order, and, if you use
more than one type of lamp in an installation, make sure that
everybody concerned knows which type of lamp goes where!

Barry Knight
English Heritage
London

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                  Conservation DistList Instance 10:69
                 Distributed: Monday, February 3, 1997
                       Message Id: cdl-10-69-008
                                  ***