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Philips introduced its first IR therapeutic lamps in 1946 under the 'Infraphil' brand, optimised for human irradiation. Whereas most IR lamps have low temperature filaments below 2500K and lives exceeding 5000 hours, the Infraphil operates at ~2900K with life ~300 hours. The short life of this consumer lamp not stimulated sales, but has a scientific basis in that the radiation peak is shifted to 1000nm and is able to penetrate much deeper into human tissue.
For IR therapy it is desirable to maximise the penetration of heat deep into the muscle, but this is limited by the onset of pain when skin temperatures exceed 44°C. This is why the Infraphil lamp was never made in powers exceeding 150W. However thanks to the wavelength shift, Philips was first with a biologically-optimised lamp whose heat was delivered below skin level - allowing an increase in power density without risk of pain, and much more effective treatment.
The original Infraphil lamp had a traditional blown glass reflector, and in 1960 it was joined by the new pressed glass lamp featured on this page. This offered a considerable improvement in performance. Pressed glass lamps normally feature a higher intensity beam - however for the Infraphil lamp the IR irradiance was maintained at the same high level, and the beam was broadened so as to treat a larger area of the body. The beam uniformity is outstanding thanks to the fresnel glass lens, and has a slightly elliptical profile - hence the continued use of a 3-pin bayonet cap to correctly orient this beam. The front lens is dyed with a ruby coating of cadmium sulphoselenide, blocking wavelengths below 600nm which would be absorbed by haemoglobin in the blood, allowing high IR levels without risk of haemolysis. |