LED photobiology

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Transcript LED photobiology

LED photobiology
János Schanda
University of Pannonia
Virtual Environment and Imaging Technologies
based on the paper by
W. Halbbritter, W Horak and J Horak:
CIE Conference Vienna, 2010
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
low risk
Blue light
Eye movement, time dependent smear effect
takeninto consideration
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,
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)
 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
Physiological (time integrated) radiance:
Radiant power passing through a defined aperture stop (pupil) at a defined
 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
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!