IEC 62471:2006 pdf free download

IEC 62471:2006 pdf free download
IEC 62471:2006 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.
Note 1: Note that the exposure time at which E B becomes independent of time is 100 s rather than the 10000 s given for L B in Equation (4.6). The reason for this change is that for exposure times greater than 100 s it was assumed that the diameter of the irradiated area of the retina increases as the square root of time. Hence the effective irradiance of the retina decreases and the retinal radiant exposure deposited becomes independent of time for exposure durations between 100 s and 10 000 s due to the assumption of task-oriented eye movements. This behaviour is shown in the graphical representation of E B in Figure 5.4.
Note 2: For ophthalmic instruments or for a stabilized eye during surgery where eye movements are minimal the exposure time is extended to 10 000 s. This implies that in such cases the blue light weighted irradiance should be ≤ 10 -2 W⋅m -2 , i.e.,100 times smaller than that given in Equation (4.7b).