Philips Infraphil KL7500
heat lamp
FRESNEL-LENSES
Compared with incandescent lamps for illumination
purposes, infrared incandescent lamps for
therapeutic use were relatively large for their typical
wattage of 100 to 150 Watts, thus enabling the
creation of a sufficient broad beam. To increase the
output and to force the infrared rays into a more or
less parallel beam, the inside of the lamp was
covered with an infrared reflective coating. From the
1950s on, impact-proof pressed glass lamps
became popular. These lamps were often equipped
with a segmented spherical lens, a so-called Fresnel
lens as can be seen with the Philips Infraphil
KL7500 therapeutic heat lamp on display here. The
lens bundled the infrared rays while its segmented
structure limited the weight of the lens.
