**9. Conclusion**

The measurement of absolute amounts of optical radiation requires careful and detailed consideration of a broad range of physical concepts and practical instrumentation to produce an accurate, reproducible and internationally acceptable result. The basis for this is the internationally defined terminology and definitions of the measurement quantities and accepted units that are useful for optical radiation measurements. We have discussed the five predominant measurement quantities and indicated the measurement configurations necessary to obtain reliable results. The geometrical relationships between these quantities have been discussed with the purpose of allowing measurement standards to be used for several different measurement quantities. Some of the requirements to measure optical radiation in a means that is relevant to the human visual response to radiation have been presented. The characteristics of incandescent sources that are a basis for most measurements have been discussed, together with the sources of errors and uncertainties that these

The complexity of photometers and spectroradiometers gives rise to many interesting

1. The failure of a photometer to match the desired photometric or colorimetric functions has been discussed in Section 4.2.5. The uncertainty in the spectral mismatch correction factor will need to be determined from the estimated uncertainties in the spectral

2. The response of the detector used in the photometer or spectroradiometer to input flux signal size must be linear to allow comparison of sources with differing amounts of

3. If the geometric distribution of the output of the lamps varies with angle or position, and if measurements of high accuracy are required, any spatial non-uniformity in the responsivity of a photometer will have an effect. The use of integrating spheres to

4. If the number of digits available in the output of the voltmeter used to measure the signal size is small, the measured signals will be subject to a digitizing error. 5. Monochromator wavelength errors. There are two possible components to this error: the deviation of the indicated monochromator wavelength from its actual value, and the ability of the monochromator to reproduce this error. The reproducibility error may give rise to a random error that can be determined using a Type A uncertainty evaluation if enough repeatable measurements can be made. The effects of an error in the monochromator wavelength calibration will predominantly depend upon the difference in the relative spectral distribution of the two sources that are being compared. If the sources have the same relative spectral distribution, the wavelength offset will cause the

6. Spectral bandwidth errors. The signal at the spectroradiometer detector is a weighted average over the spectral bandwidth of the monochromator. If the spectral distribution of the source changes rapidly over this bandwidth, much of this spectral information

More detail concerning these and other effects may be found in several of the references

The measurement of absolute amounts of optical radiation requires careful and detailed consideration of a broad range of physical concepts and practical instrumentation to produce an accurate, reproducible and internationally acceptable result. The basis for this is the internationally defined terminology and definitions of the measurement quantities and accepted units that are useful for optical radiation measurements. We have discussed the five predominant measurement quantities and indicated the measurement configurations necessary to obtain reliable results. The geometrical relationships between these quantities have been discussed with the purpose of allowing measurement standards to be used for several different measurement quantities. Some of the requirements to measure optical radiation in a means that is relevant to the human visual response to radiation have been presented. The characteristics of incandescent sources that are a basis for most measurements have been discussed, together with the sources of errors and uncertainties that these

distribution functions for the contributing sources and the photometer.

radiation output. This effect can also include the associated electronics.

same relative effect for both sources, resulting in no error in calibration.

mitigate this source of error was discussed in Section 6.2.

will be lost in the averaging process.

**9. Conclusion** 

(CIE 063:1984, Grum & Becherer, 1979, Kostkowski, 1997).

**8.2.2 Radiation detectors** 

sources of error.

characteristics present. The basic concepts of the photometers and spectroradiometers that are used to measure the radiation output from these sources have been presented with the aim of providing a reliable foundation for basic metrology and applied measurements. The necessity of international acceptability of goods and services, energy efficiency, and consumer safety have encouraged the development of more accurate, versatile and reliable equipment both to produce a wider variety of radiation sources and better means of determining their suitability to the desired application. The basic concepts and techniques described in this chapter should provide the necessary tools to pursue these goals.

#### **10. References**

