NATS 1870 Lecture 12: Filters
21 Jan 2019
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Document Summary
Filters affect the spectral composition and intensity of incident white light. Filtering methods: absorption: certain wavelengths or all wavelengths are selectively absorbed, scattering, re-direction of light beam, this re-direction can be of either all wavelengths or just certain wavelengths. Interference: bi-refringence, narrow range of wavelengths transmitted. Components of filters: light absorbing or re-directing material, dispersed individual dye molecules, fine particles of pigment, transition metal ions like cobalt, supporting medium a. In stage lights, this is gelatine: otherwise, it can be plastic, glass plates, and celluloids. Stage lights: used to have a tungsten light source, which is then covered in front by a filter. The tungsten light bulbs tend to get super hot because they"re not very energy efficient and mainly produce red and infrared light. This causes a problem in stage lighting where the filters melt and deform easily. If the filter is blue, it will absorb all of the long (red) wavelengths, and therefore melt quickly.
