As light bulb filament increases temp. its spectrum shifts red to blue.

As light bulb filament increases temperature, its spectrum shifts red to blue. When voltage is applied with a variac, a tungsten halogen bulb filament is heated by electrical resistance so that the filament emits light by blackbody radiation. The light is sent through a slit and a diffraction grating (19.050 lpi), and the continuous emission spectrum is projected and focused on a screen. As the filament is heated from red (about 1000K) to yellow or white (about 2000K), the light of the spectrum shifts from a concentration in the red region more to the blue region. i.e.: as the temperature of the filament rises, the intensity of the emitted radiation is strongest at higher and higher frequencies. Ref.: Physics For Scientists & Engineers,-Giancoli,2nd Ed., p.867-869