led photobiology
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
LED photobiology János Schanda
University of PannoniaVirtual Environment and Imaging Technologies
Laboratorybased 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, photo-conjuntivitis 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 cathegories- acceptance angles
exempt low risk moderate risk
Unit
Blue light 0.1 0.011 0.0017 radThermal 0.011 0.011 0.0017 radThermal weak visual stimulus
0.011 0.011 0.011 rad
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, 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 de
2/(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 mrada 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!