LIGHT SOURCES 



5 kW. The larger lamps do not have brighter arcs, but simply bigger arc 



areas. 



The strong emission line at 365 m^ in the ultraviolet with mercury 

 discharge lamps is frequently used for inducing fluorescence in certain 

 materials. By using a Wood's glass filter this radiation can be isolated 

 from the visible spectrum, and also from the shorter wavelength emissions 

 at 313 and 334 m/.i, which can cause a dangerous and painful conjunctivitis 

 of the eyes, even with short exposures. The 125 W Type MB w/v lamp is 

 a mercury vapour discharge lamp with a Wood's glass bulb around it. It 

 can be used close to the skin and eyes without danger. Philips Electrical 

 Ltd. now manufacture a useful 40 W tubular mercury lamp with a special 

 dark blue glass which is almost opaque to visible radiation (Figure 28.14) 



3P00 



2^500 



APOO 



a;5oo 



Figure 28.14 Energy distribution curve for a Philips'' 

 TL Blacklight Blue fluorescent lamp 



for fluorescent studies. If all the visible and shorter ultraviolet radiations 

 are required a useful small ultraviolet lamp is the Philips OZ 4 W which 

 requires a 24 V, 0-35 A supply, the lamp itself dissipating about 4 W. 

 It can be used for generating ozone, as the special glass bulb is transparent 

 to the shorter ultraviolet radiations. In consequence the eyes must be 

 screened. 



Table 3 gives the main spectral lines in mercury vapour discharge lamps, 



TABLE 3 



The Main Spectra Emission Lines From a Mercury Vapour 



Discharge Lamp With Suitable Isolation Colour Filters 



347 



