Photobiomodulation is a non thermal technique by using non ionising radiation like LED & LASER in order to relief the pain, increase tissue healing and reduce inflammation. Regarding the effect of Photobiomodulation in different Medical ,Dental and Veterinarian fields; we will highlight the definition, mechanism of action, advantages, indications and contraindications of the process. We will give you an idea about the difference between LED Vs LASER and red Vs blue Lasers. Finally we will demonstrate the idea of conversion of stress cells to healthy cells.