Brochure

www.osram-os.com
13 / 192018-08-16 | Document No.: AN097
Figure 12: Irridance correction coefficient k vs. viewing distance for the SFH 4780S
Eye safety
For the SFH 4780S used for iris recognition the IEC-62471 standard is relevant.
4
In general three exposure limits are given for IR-A radiation:
• infrared radiation hazard exposure limits for the eye (cornea)
• thermal hazard exposure limit for skin (t < 10 s)
• retinal hazard exposure limit
To calculate the irradiance for any given distance d equation 2 can be used:
Note: The distance dependent irradiance correction factor k in equation 2 is
k ~ 1.0 for distances > 5 cm from the SFH 4780S top surface. For distances
below 5.0 cm the correction factor is k < 1.0 (see Figure 12). Empirically k can be
expressed as (for the SFH 4780S):
For repetitively pulsed IR-LEDs the weighted radiant exposure E
e,time,avg
(t
avg,max
= 0.25 s) shall be compared with the continuous wave exposure limits
(EL) by using the time averaged values of the pulsed emission as long as E
e
of
the single pulse does not exceed any limit on its own.
4. Please note that the following discussion is based on T
a
= 25 °C. At lower temperatu-
res the limits can be higher, please refer to the IEC-62471 standard.
Distance [cm]
Irradiance correction factor k
0.7
0.6
0.4
0 2 14 18 20
1.0
0.8
0.5
610
0.9
412128
E
e
k
I
e
d
2
------
= 2
k 1 e
13 5,– d 
05,
e
50– d 
–– 3
E
eavg ,
E
epulse ,
DE
epulse ,
t
pulse
t
period
-----------------
== 4