Light source for an inline sensor having one or more solid state UV emitters for emitting light at single wavelengths in the range of 240 to 400 nm. The light emitted by each of the emitters has a bandwidth on the order of 10-20 nm and is directed toward a measurement detector in the inline sensor. The UV emitters are enclosed in a housing which can be attached to the inline sensor, with a reference detector and a regulator for the UV emitters also within the housing, and an aperture through which the light passes from the emitters to the measurement detector. In some embodiments, air cooling is provided for the UV emitters.