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, 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 rad

Thermal 0.011 0.011 0.0017 rad

Thermal 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!