Osram G157 heat lamp
the Osram Theratherm heat lamp emitted infrared radiation as well as yellow/white light
With further increasing levels of energy the
frequency of the radiation would shift towards yellow
and even blue while the intensity of the light
increased, the result being the bright yellow/white
light as produced by incandescent lamps. The
contribution of the (for medical purposes) desired
short wave infrared radiation was significantly
greater than that of a Kanthal or Chromel element
but the amount of visible light was even greater and
this could cause eye problems during a medical
treatment. For this reason, most incandescent
lamps for medical purposes came with red coloured
eye protectors or they were equipped with an
additional or an integrated red coloured filter, as with
the Osram Theratherm heat lamp in an Osram G157
armature on display here.