LED photobiology

Report
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
Overview


Introduction
Optical radiation
LED emission spectra
 Human eye transmission


Optical hazards

Conclusions and summary
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

LED emission




LEDs now available from 245 nm
Visible wavelengths + white
Near infrared – optical communication
LED spectrum bandwidth: 20 nm – 40 nm
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.

Ocular hazards
Photokeratitis, photoconjuntivitis
 Redening of the eye,
disapers within 24 –
48 hours
Optical hazards

Chemical – biochemical hazards
Photon energy in the range of energy of
chemical bonds
 Skin damages
 Ocular damages


Thermal hazards
Skin damages
 Ocular damages

Eye hazard spectra after CIE
TC 6-55 draft report
Lamp risk cathegoriesacceptance angles
exempt
low risk
Unit
0.011
0.011
moderate
risk
0.0017
0.0017
Blue light
Thermal
0.1
0.011
Thermal
weak
visual
stimulus
0.011
0.011
0.011
rad
Eye movement, time dependent smear effect
takeninto consideration
rad
rad
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

„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.
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

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
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
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:
a = 2 arctan(apparent source size/2 sourcedistance)
a But amin=1.7mrad, amax=100 mrad
a Apparent source position
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
Example: p-LED, individual LED
LED-lamp based on LED
component evaluation
CIE S009/IEC62471
requirements, 1
CIE S009/IEC62471
requirements, 2
Thanks for your kind attention!

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