Low pressure mercury vapour discharge lamps serve very little use in the area of general lighting (except for fluorescent tubes, which *are* phosphor coated low pressure mercury vapour tubes - they however are documented in their own section).  This is due to the fact that at lower pressures, the mercury discharge produces a lot of shortwave UV radiation, but relatively little visible light. 

This is however highly desirable in some situations; most notably where a phosphor can be used to 'downconvert' this shortwave UV into visible light, or where the UV itself can be useful - such as germicidal applications.  Low pressure spectral lamps are also produced to allow the spectral characteristics of this discharge to be analysed, some with and some without UV transmitting outer jackets.

Philips 92123E Low Pressure Mercury Spectral Lamp


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