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!