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17 / 192018-08-16 | Document No.: AN097
Figure 15: Exposure limit (L
R
) versus exposure time (retina) for different angular subtens
(α
max
= 0.1 rad, α
min
according to IEC-62471)
• Example 1: SFH 4780S biased with 500 mA (DC) for t = 9 s, assuming
I
e
= 2.2 W/sr (estimated maximum I
e
level at 500 mA). The limit according
to equation 12 (α = 0.1 rad, for distances < 2.8 cm) is 288.7 kW/(m²sr). This
compares favorably to the actual L
R
= 168 kW/(m²sr) from to equation 11.
This essentially means that this operating condition is eye safe concerning
the retina case.
• Example 2: SFH 4780S biased with 500 mA, 50 ms pulse-on time
(I
e
= 2.2 W/sr), four pulses a second, and total operating time of 9 s. The
limit according to equation 12 (with α = 0.1 rad at < 2.8 cm distance) is
288.7 kW/(m²sr). Comparing this with the actual average radiance of
34 kW/(m²sr) indicates that this operating condition causes no harm to the
human retina.
General considerations
As seen, eye safety can be a concern for this kind of high-power, high-radiant
intensity devices. However, certain operating conditions (drive current, pulse
width, duty cycle) and the use of cover glasses / optics in front of the SFH 4780S
Time [s]
L
R
, L
IR
EL radiance [mW/mm²/sr]
10
6
10
5
10
4
10
3
10
2
10
1
110
2
10
2
10
2
10
-3
10
-4
10
-5
10
Irradiance cornea
Irradiance skin
10
-2
10
-1
L
Rlim 10 sec
6000 W  m
2
 sr 

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