1. LED photobiology János Schanda University of Pannonia
Virtual Environment and Imaging Technologies Laboratory
based on the paper by
W. Halbbritter, W Horak and J Horak:
CIE Conference Vienna, 2010

2. Overview Introduction Optical radiation Optical hazards
LED emission spectra
Human eye transmission
Optical hazards
Conclusions and summary

3. Optical radiaton - photobiology
UltraViolet radiation: actinic radiation
UV-A: 315 m – 400 nm
UV-B: 280 nm – 315 nm
UV-C: 100 nm – 280 nm
Visible radiation: 380 nm – 780 nm
Infrared radiation
IR-A: 780 nm – 1400 nm
IR-B: 1.4 mm – 3 mm
IR-C: 3 mm – 1 mm

4. LED emission LEDs now available from 245 nm
Visible wavelengths + white
Near infrared – optical communication
LED spectrum bandwidth: 20 nm – 40 nm

5. Penetration of UV radiation into the eye
After Sliney DH, Wolbarsht ML. Safety with Lasers and Other Optical Sources. (New York: Plenum Publishing Corp); 1980.

6. Ocular hazards Photokeratitis, photo-conjuntivitis
Redening of the eye, disapers within 24 – 48 hours
Ocular hazards

7. Optical hazards Chemical – biochemical hazards Thermal hazards
Photon energy in the range of energy of chemical bonds
Skin damages
Ocular damages
Thermal hazards

8. Eye hazard spectra after CIE TC 6-55 draft report

9. Lamp risk cathegories- acceptance angles
exempt
low risk
moderate risk
Unit
Blue light
0.1
0.011
0.0017
rad
Thermal
Thermal weak visual stimulus
Eye movement, time dependent smear effect takeninto consideration

10. Lamp safety measurement conditionsof
Measurement distance:
Minimum viewing distance: 200 mm
GSL lamps: 500 mm
Measurement aperture:
Maximum human pupil size: 7 mm
Source size and angular subtense:
Thermal retinal hazard depends on irradiated surface (heat flow)
380nm-1400nm: eye focuses- minimum angular subtense: amin=1.7mrad
Maximal angular subtense: amax=100mrad

11. „Physiological” radiance/irradiance and time average
Radiance weighted according tothe action spectum of the given hazard
Thermal effects: important the heat conduction of the tissue away from the irradiation site, the irradiated tissue volume and the irradiance – local burn.
Size of irradiation importan!, irradiance dependent, W/m2.
Photochemical effects: strong wavelength dependence, follows Bunsen-Roscow law.
Radiant exposure, J/m2, dependence.

12. Ocular hazards
Radiation between 380 nm and 1400 nm reaches the retina.
Light source focused on retina
Retinal irradiance:
Er = p Ls t de2/(4f 2)
where:
Er: retinal irradiance
L s: source radiance
f: : effective focal length of eye
De : pupil diameter
t : transmittance of ocular media
A worst-case assumption is: Er= 0.12 L s
This linear dependence of retinal irradiance of source radiance breaks down for small sources, lasers.
Thus retinal safety limits for 300/380 nm – 1400 nm are given in W/m2 or J/m2

13. Lamp safety regulation measurements
Physiological (time integrated) radiance: Radiant power passing through a defined aperture stop (pupil) at a defined distance
Aperture area defines solid collection angle W (sr) and measurement area: field of view:FOV (m2), measured by the acceptance angle: g

14. Time dependence of acceptance angle to be used
Due to eye movents for short durations small acceptance angles have to be chosen
FOV can be over- or under-filled

15. Product safety standard conditions
Measurement distance
200 mm meas.distance
(GSLs: 500 lx distance)
Measurement aperture: maximum pupil size, 7 mm diameter
Source size & angular subtense
Thermal hazard source image size dependent:
= 2 arctan(apparent source size/2 sourcedistance)
But amin=1.7mrad, amax=100 mrad
Apparent source position

16. Product safety issues
CIE S 009/IEC 62471: Photobiological Safety of Lamps and Lamp Systems
Lamp and lamp system manufacturer requirements
If applicable FOV<source area (overfilled)-> ->LED radiance data hold for luminaire
If underfilled, multiple small sources can fall into the FOV area and averaged radiance will sum up!
For such applications the tru weighted radiance of the source is needed, acceptance angle should not be smallerthan 1.7 mrad.
But LED assembieswith beam shapingoptics have tobe measured according to the standard.
P-LEDs(and blue LEDs) might exceed the low-risk group

17. Example: p-LED, individual LED

18. LED-lamp based on LED component evaluation

19. CIE S009/IEC62471 requirements, 1

20. CIE S009/IEC62471 requirements, 2

21. Thanks for your kind attention!