A light guide includes: an optical medium; and light-scattering particles each
having a scattering cross section and being contained in the optical medium
with a density Np so that light which enters the light guide from a
first end face can propagate to a second end face while being scattered by the
light-scattering particles. In the light guide, the product of the scattering cross
section , the density Np, the length LG of the optical
medium in the light propagation direction, and a correction coefficient Kc
is less than or equal to 0.9. Preferably, the product is less than or equal
to 0.4 combining a plurality of optical mediums.
