Mercury Vapour Lamps
Mercury and Halide Lamps
Mercury became popular in discharge tubes early on as it produces a strong blue- green light. They also emit Ultra-Violet; this can be used to fluoresce compound giving other colours to mix with the mercury discharge and create white light as in the fluorescent tube. use mercury at low pressure and where in common use in offices and home for many years. This example is of a germicidal UV light. The tube wall is uncoated and made form quartz rather than glass. Quartz transmits UV light which is harmful and doesn't pass through the glass a normal fluorescent.
The pictures on the left shows an early MA/V 250W medium pressure mercury lamp. These lamps were succeeded with the high-pressure version once quartz arc tubes could be manufactured. Quartz was required due to the high running temperature of the arc.
The MB/U 250W lamps is electrically identical to the MA/V above and could be fitted into older fitting. Both these lamps have been obsolescent for quite a few years due to their poor colour rendering properties.
The addition of a fluorescent coating to the outer bulb forming the MBF/U lamp further improved the light output and reduce glare. The outer coating would convert UV to a red/orange to improve the colour. These became superseded with the introduction of metal Halide which offer improvements in both efficiency and colour.
Mercury Halide Lamps
By adding halides to the mercury arc the light temperature and colour can be controlled. This result is light output close to that of tungsten. Although still a line spectrum the Red, Blue and Green activity can be balanced to trick the eye. This technique is so versatile coloured architectural lighting can be produced.
The halide lamps shown are a 400W GE multi-vapor MRV400/U/40 white halide lamp and a 150W Blue halide lamp below.
The spectral images below are for high pressure mercury lamps (MB/U) and (MBF/U) not the red spectral lines introduced by the fluorescent coated outer bulb. The lower spectra belong to a white metal halide lamp and a blue metal halide lamp. Notice many other lines are still present in the blue halide but the blue predominates greatly.