The effect of background beam with different Glass constant on the relative spatial refractive perturbation in photovoltaic crystal was discussed, in which was introduced the concrete conditions for the formation of bright or dark photovoltaic spatial solitons in crystals with negative refractivity change. Based on the results, for what is to our knowledge the first time, the bright photovoltaic solitons was experimentally observed in LiNbO3:Fe by use of e-ray signal of 532nm and o-ray background illumination of 488nm.