Transillumination

Transillumination (from Latin trans - through and Latin illuminare - to illuminate) is a phenomenon that occurs when light passes through a translucent body.

With transillumination, light passing through the body can be partially absorbed and re-emitted in a different spectral range. As a result, at the exit from the body a spectrum is observed that is different from the spectrum of the incident light. The phenomenon of transillumination is widely used in medicine and technology to study the structure of transparent bodies, for example, biological tissues.

Transillumination is also used in optics to determine the density and state of matter. So, when white light is passed through graphite, the latter begins to glow red. This suggests that graphite contains defects that absorb light in the blue and green parts of the spectrum and re-emit it in the red.

The phenomenon of transillumination was discovered in 1756 by the French scientist Charles Francois Dufay.