Radiometry Light Measurement

Manipulating light for more accurate measurement

Light waves behave like all electromagnetic waves, in that they interfere with each other, become directionally polarized, or bend when passing an edge. Because of these properties, light waves can be predictably manipulated for increased or decreased amplitude or even filtered by wavelength or a band of wavelengths by means of various filters, mirrors, lenses, prisms, gratings, and other input optics. These principals make it feasible to tailor a light detector to match a particular application. In most cases when making radiometric measurements with silicon photodiodes, a flat spectral response filter is used to even out the detectors innate sensitivity to the red portion of the spectrum versus the blue. This flat response allows the detector to accurately measure light at one wavelength versus another which is particularly useful if the spectral output of the light source is unknown or likely to vary with operating conditions or application requirements. In the event that a particular section of the output from a light source needs to be isolated, a detector with a narrower response can be used or a band pass filter can be placed on a broad response detector to tailor it’s response to measure just the required portion of light. Narrowband filters can also be used to isolate a very narrow portion of light such as that of a specific mercury emission line.