You don?t need both but keep in mind, very often a colorimeter will produce better results with a display than a Spectroradiometer (a Spectrophotometer uses a light source to measure something, the same device with the light source off, reading light radiating from a display is technically called a spectroradiometer).
Spectrophotometer break the colors into bands. Colorimeters are often much better and reading black levels because the data is not broken down to this degree and it?s often less expensive and easier to produce colorimeters with filters that are better designed for reading a display. The OPTIX xr is an example of a state of the art colorimeter designed with special filters (and internal cooling) that really shine on LCDs.
Bottom line is you can use a spectroradiometer on a display and it?s a multi-tasker but it?s not necessarily the best instrument for the job just because it?s more expensive.
Andrew Rodney
www.digitaldog.net