I used light to transform a colloidal solution of spherical silver nanoparticles into larger triangular nanoparticles. The particle size and shape can be controlled by choosing the wavelength(s) of light used to drive the photochemical growth. These findings suggest a new way of thinking about growth of nanoparticles in solution and show the exciting possibility that light can be used as a major control parameter in metallic nanoparticle growth reactions. I have used different colour transparent filters (red, green, dark green, blue) in photoreactor and with different wavelength (three different red and one green) LED’s in my experiments. I monitor the evolution of the reaction at regular intervals by means of a commercial UV/vis spectrophotometer; the final products and some important intermediates are further characterized by transmission electron microscopy (TEM, 100 kV) and scaning electron microscopy (SEM). Particle size distribution was calculated using 100 or 200 particles from TEM pictures and using Image Tool software.