A control apparatus for an internal combustion engine where the inside of a combustion chamber is divided into a layer of internal EGR gas and a combustible layer to perform stratified combustion. The layers of the dielectric stack are selected to maximize reflection of light incident at angles ranging from 10 to 30 degrees, relative to the substrate. The wavelocker is configured to drive the light source such that said multiple wavelengths coincide with the ITU grid. In a preferred embodiment, acrolein which has been obtained from glycerol based on renewable raw materials is used.