A diffraction grating, made of fine parallel slits,

can have as many as 10,000 lines per centimeter. The

equation for a single slit may be used for approximate

calculations. The device used to measure light wave-

lengths with a diffraction grating is called a grating

spectrometer. The central maximum of the interference

pattern remains the same color as the light source.

When monochromatic red light falls on the device, a

series of bright bands are seen on the left and right

side of the central maximum.

When white light falls on the device, each red band is replaced by a spectrum. The red band in the spectrum is at the same location as when monochromatic light is used.