Diffraction gratings are of two types; transmission grating and reflection grating.
- Transmission grating: When a wavefront is incident on a grating surface light is transmitted through the slits and obstructed by the opaque portion. Such a grating is called a transmission grating.
- Reflection grating: When the lines of grating surface are drawn on a slivered surface then light is reflected from the position of the mirror in between any two lines. Such surfaces act as reflection gratings.