AS NZS IEC 62471:2011 pdf free download – Photobiological safety of lamps and lamp systems
4.2.2 Angular subtense of source and measurement field-of-view
For radiation in the wavelength range 380 nm to 1400 nm the area of the retina irradiated is an important element in determining the EL’s for both the blue light and retinal thermal hazards. Since the cornea and lens of the eye focuses the apparent source on the retina the best method to describe the irradiated area is to relate this area to the angular subtense of the apparent source, α . Due to physical limitations of the eye the smallest image that can be formed on the retina of a still eye is limited to a minimum value, α min , even for a point source. In this standard the value for α min is 0,0017 radian. Measurements of emitted radiation from apparent point sources, either pulsed or very high radiance continuous wave sources, that relate to the retinal thermal ELs at 0,25 second (blink reflex time), shall use the 0,0017 radian angular subtense as the measurement field of view.
5. MEASUREMENT OF LAMPS AND LAMP SYSTEMS
The measurement of optical radiation for the purpose of computing photobiological radiation values poses significant challenges for the radiometrist. Typical photobiological action spectra such as S UV ( λ ) have rapidly changing values with slight change in wavelength. Furthermore, transmission of radiation from lamp sources with glass envelopes have rapidly increasing output with increasing wavelength in the region where S UV ( λ ) is rapidly decreasing. Hence issues of accuracy of the weighted results must be thoroughly considered. While irradiance measurements are routinely performed, radiance measurements are not routine and often difficult to make, especially for the photobiological hazards, as they involve a field of view that changes depending on the hazard evaluation. For these reasons it was thought necessary to include a rather lengthy discussion on the conditions and procedures needed to make emission measurements that will be used to assign risk group classification of various lamps and lamp systems. It should be noted that the measurement procedures described in this standard are designed to account for biophysical phenomena. Specifically, they can involve averaging over apertures or field-of- views which would be considered inappropriate for general radiometric measurements. However, hazards might be overestimated if non-averaged measurement values were to be compared with the respective exposure limits. To better provide a comparison of the various exposure limits, developed in clause 4.3, including the effects of the field-of-view, both a tabular and graphical summary are shown at the end of this clause. Thus Figure 5.4 and Table 5.4 summarizes the maximum values for each of the irradiance based hazard exposure quantities as a function of exposure time, while Figure 5.5 and Table 5.5 summarizes the maximum radiance based (retinal) hazard exposure quantities, also as a function of exposure time.