A halogen lamp has an iodine-cycle tungsten incandescent lamp as the visible/near infrared (360 nm to >1 pm) light source for spectrophotometry and phototherapy, and recently
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it has also been used in IR phototherapy. As it is gas-filled, the tungsten electrode can be heated up to 4000 K. At this temperature, the maximum spectra of emission is about 1max =750 nm (see Fig. 3.1). About 30% of the total power is emitted at wavelengths shorter than 1max and the remaining 70% is emitted at wavelengths longer than 1max.