**5. Conclusion**

(11)

(12)

The following are the descriptions of the abovementioned uncertainty budget items:

repeatability of the lamp.

lamp is estimated to be 1.0%.

where

88 Metrology

erence [29] by the following Equation [10, 37]:

is the relative spectral output of the test source;

is the relative spectral output of the standard source;

Calibration of primary standard lamps **B** Aging of standard lamps **B** Self-absorption correction **A** Spectral mismatch correction **B** Repeatability of test lamps **A** Spatial nonuniformity of the sphere response **B** Lamp electrical control **A**

**Relative combined standard uncertainty Relative expanded uncertainty (k = 2)**

is the relative spectral responsivity of the photometer; and.

• **Calibration of luminous-flux standard lamps:** The uncertainty of the luminous-flux standard lamps is stated in the calibration report issued by the national laboratory or the calibration laboratory that performed the calibration. This uncertainty normally includes the

• **Aging of standard lamps:** This uncertainty is calculated from the aging rate of the standard lamps and their calibration intervals. For example, if the aging rate is 0.02% per hour and the lamp is recalibrated every 50 h of its burning time, the uncertainty due to aging of the

• **Spectral mismatch correction:** Uncertainty of the determination of the spectral mismatch correction factor u(SCF) which can be determined regarding Eq. (11) and according to ref-

• **Self-absorption correction:** Uncertainty of the determination of the correction factor.

is the spectral luminous efficiency function that defines a photometric measurement.

**Uncertainty factor Type Relative standard uncertainty (%)**

**Table 2.** Typical uncertainty budget for luminous intensity calibration (source-based method) [9].

In this chapter, we concentrate on the measurement of absolute amounts of optical radiation, which requires careful definition for the photometric and radiometric quantities such as total flux, intensity, illuminance, luminance, radiance, exitance and irradiance. Also, it was necessary to distinguish between the difference of the exitance and irradiance quantities in the physical meaning. The metrological traceability chain is the sequence of measurement standards and calibrations that were used to relate the measurement result to the reference. To produce accurate, reproducible and international acceptable results, the measurement of absolute amounts of optical radiation needs careful and detailed consideration of a broad range of physical concepts. A measurement has imperfections that give rise to an error in the measurement result. Therefore, measurement results should be expressed in terms of estimated value and an associated uncertainty. Actually, an error is viewed as having a random component and a systematic component. Random error presumably arises from unpredictable variations of influence quantities and is not possible to compensate for the random error of a measurement, but increasing the number of observations can usually reduce it. We provide an explanation to how to estimate and build the uncertainty budget of measurements for the most important quantities. The components of a typical uncertainty budgets for luminous intensity calibrations (detector-based method) and total luminous flux measurements are represented and explained in detail in this chapter.
