PHOTOGRAPHIC LIGHT SOURCES 



263 



Light impinging upon a medium is dispersed in three ways as shown in Fig. 3. 

 Part of the light may be reflected, as already explained, or, if the medium is trans- 

 parent, much of the light may be transmitted through it. The rest is absorbed in 

 passing through the medium and is dissipated^ ultimately making its appearance in 

 the form of heat. 



IncicJerrf beam 



Refleci-eol beam 



Smooth, po/ishec/ 

 ■ surface 



Speculoir or Regular Reflec+ion 



Fig. 2. 



^,E-hchec/ or 

 ^/ granular surface 



Diffuse Reflec+ion 



-Diagrams illustrating specular reflection from polished surface and diffuse reflection 

 from surface which is irregular compared with dimensions of light waves. 



Incident beam Reflected rays 



Transmitted rays 



Fig. 3. — In passing through a transparent medium, some of the light rays are reflected, 

 some are absorbed, and the rest are transmitted through the medium. The rays are bent 

 in passing from two mediums having different indices of refraction. 



The velocity of light in any material medium is less than the velocity in free space. 

 Therefore, if light which is traveling through a vacuum is made to pass through a 

 transparent medium, its velocity will be decreased. If the incidence is perpendicular 

 or normal to the surface of the medium, the only effect will be a slowing down of the 

 velocity of light while passing through the denser medium. However, if light impinges 

 on the denser medium at some other angle, the relative change in velocity of propaga- 

 tion through the denser medium will result in a bending of the beam. At the surface 

 of the two mediums the direction of the beam will change, and the light is diffracted. 



