ABSTRACT
The “red light syndrome” was well known, and much experimental work was done in the first third of this century. Red light was used in medicine even in ancient times, and curing with red light was among methods used by N. R. Finsen, the father of contemporary phototherapy. The He-Ne laser was the first commercially available source of coherent light. It is no wonder that the stimulating effect of light, and red light in particular, was rediscovered when coherent light sources were used. Spatial coherence of light means the harmony of the phases of the light wave at different points in space. The spatio-coherent wave may with the aid of an optical system be focused on area of order of length of light wave restricted by diffraction. The conclusion that under normal physiological conditions, the absorption of low-intensity light by biological systems is of a purely noncoherent, is verified by the experimental work done in “prelaser” times.
