Combining an LED with collimation optics generates a relatively homogeneous light beam, which eases power measurements (see below) and allows for even irradiation of the photoreactor. Furthermore, the collimated beam allows for use of dichroic beam combiners, using which the output from multiple LEDs can be combined. This is particularly useful when simultaneous irradiation with two wavelength regions is desired. There are multiple vendors offering collimated LED light sources and corresponding beam combiners (e.g. Mightex or Prizmatix).