The spatial spreading behavior of glass particle-dispersed epoxy matrix optical composites has been observed, and the composites used have light transmittance in the visible wavelength region. The effect of (i) particle volume fraction, (ii) particle size and (iii) refractive index difference between the particle and matrix on the spreading behavior are discussed. The spatial spreading behavior of transmitted light from a back surface of the composites is found to be strongly correlated with light scattering behavior of the composite. The increase of spatial light spreading also increases spatial light transmittance of the composite. (C) 2003 Kluwer Academic Publishers.