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The pinnacle of this type of construction was the General Electric DHJ lamp
that had its 500 W filament above the mirror, which answered the problem of
how to minimise the heat getting to the slide. However, that made the top of the
lamp incredibly hot and needed a cooling fan that was very loud.
Europe did not follow the American
construction with built-in mirrors.
From the beginning Philips and Osram
used reflecting glass in their lamps.
They did this already in diascope pro-
jectors and Philips had the idea of pro-
ducing the 110 V 750 W P28 nr 7079
with a built-in reflector. The manufac- Fig 15. General
turers of 16 mm sound projectors had Electric DHJ
decided not to build-in condensers any more and they did
not follow Philips any longer.

The pinnacle of the reflecting glass lamps was the 8 V 50
Fig 16. Left: 220 V 100 W E27, Right: 110
V 750 W nr. 7079. W for 8 mm movie projectors. Here Philips and Osram
worked together. They took the 12 V 100 W filament as a
starting point but now made it smaller and inside it was wholly reflected: all the surface around
the actual light source was like a mirror. Except for the area of the lamp where the light came out,
the whole lamp was covered with reflecting material. This lamp later became known as the
‘Spaceman’. With this lamp it was not necessary to have a condenser and a heat filter in the
projector. Thanks to these changes the result on the screen was the same as with the 12 V 100 W
lamp with its external mirror. Many projector manufacturers followed, using this lamp in their
products. Later came another lamp like the 12 V 100 W but with a different base. It was especially
used in some Eumig projectors but other factories did not use it.
The 8 V 50 W lamps had been the start of the wish of Philips and
Osram to create a light POINT that was kept in a mirror; one that was
able to reduce the heat and to concentrate all the light available. The
first step was to improve the durability of the light. The globes so far
had a relatively short life because the filament evaporated and vapour
was precipitated on the inside of the glass. As a result, (a): The glass
became dark and the lamp gave less light, and (b): The filament
became thinner and thinner till it broke. They used iodine, which
doubled the lamp life to 50 hours but at the cost of a temperature of
600º C. At a lower temperature it worked as usual but the lamp soon
became dark. Normal glass melted around 300º C so they used quartz
glass. Quartz glass is sensitive to the acids produced by the human
skin and you should therefore avoid touching the lamps with bare
hands. Fig 17. 8 V 50 W lamp.

For cine lights the iodine did not do such a good job. In some lamp containers the gas sank to the
bottom and that resulted in a shorter lamp life. Using bromine instead of iodine cured this. Now
they had to change the name of the lamp with each change of gas, so they decided to use the
family name of the gases: halogen. The lamp was called the halogen quartz lamp. The 12 V 100
W type was mostly used in 8 mm movie projectors and the 24 V 150 W in slide projectors. But
other lamps followed.