LED photobiology János Schanda University of Pannonia Virtual Environment and Imaging Technologies Laboratory

Overview Introduction Optical radiation Optical hazards LED emission spectra Human eye transmission Optical hazards Conclusions and summary

Optical radiation - photobiology Ultra Violet 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.

Optical hazards Chemical – biochemical hazards Thermal hazards Photon energy in the range of energy of chemical bonds Skin damages Ocular damages Thermal hazards

Some photobiological hazard definitions see CIE S 009:2002 Photobiological safety of lamps and lamp systems actinic dose (see ILV 845-06-23) Quantity obtained by weighting spectrally the dose according to the actinic action spectrum value at the corresponding wavelength. Unit: J⋅m -2 Note: This definition implies that an action spectrum is adopted for the actinic effect considered, and that its maximum value is generally normalized to 1. When giving a quantitative amount, it is essential to specify which quantity dose or actinic dose is meant, as the unit is the same. angular subtense (α) Visual angle subtended by the apparent source at the eye of an observer or at the point of measurement. Unit: radian Note: The angular subtense α will generally be modified by incorporation of lenses and mirrors as projector optics, i.e. the angular subtense of the apparent source will differ from the angular subtense of the physical source.

Some photobiological hazard definitions see CIE S 009:2002 Photobiological safety of lamps and lamp systems blue light hazard (BLH) Potential for a photochemically induced retinal injury resulting from radiation exposure at wavelengths primarily between 400 nm and 500 nm. This damage mechanism dominates over the thermal damage mechanism for times exceeding 10 seconds. erythema (see ILV 845-06-15) Reddening of the skin; as used in this standard the reddening of the skin resulting from inflammatory effects from solar radiation or artificial optical radiation. Note: The degree of delayed erythema is used as a guide to dosages applied in ultraviolet therapy. ocular hazard distance Distance from a source within which the radiance or irradiance for a given exposure duration exceeds the applicable exposure limit. Unit: m

general lighting service (GLS) lamps Some photobiological hazard definitions see CIE S 009:2002 Photobiological safety of lamps and lamp systems general lighting service (GLS) lamps Term for lamps intended for lighting spaces that are typically occupied or viewed by people. Examples would be lamps for lighting offices, schools, homes, factories, roadways, or automobiles. It does not include lamps for such uses as film projection, reprographic processes, "suntanning", industrial processes, medical treatment and searchlight applications. large source Size of the source image on the retina which is so large that radial heat flow in the radial direction from the centre of the image to the surrounding biological tissue is negligibly small compared to heat flow in the axial direction.

Some photobiological hazard definitions see CIE S 009:2002 Photobiological safety of lamps and lamp systems photokeratoconjunctivitis Inflammatory response of the cornea and conjunctiva following exposure to ultraviolet (UV) radiation. Wavelengths shorter than 320 nm are most effective in causing this condition. The peak of the action spectrum is approximately at 270 nm. Note: Different action spectra have been published for photokeratitis and photoconjuctivitis (CIE 106/2 and CIE 106/3–1993); however, the latest studies support the use of a single action spectrum for both ocular effects (CIE 106/1–1993). retinal hazard region Spectral region from 380 nm to 1400 nm (visible plus IR-A) within which the normal ocular media transmit optical radiation to the retina. exposure limits Individuals in the vicinity of lamps and lamp systems shall not be exposed to levels exceeding the limit exposure limits apply to continuous sources where the exposure duration is not less than 0,01 ms and not more than any 8-hour period.

Eye hazard spectra after CIE TC 6-55 draft report

Actinic UV hazard spectrum for skin and eye

Blue light hazard Retinal blue light hazard exposure limit To protect against retinal photochemical injury from chronic blue-light exposure, the integrated spectral radiance of the light source weighted against the blue-light hazard function, B(λ), i.e., the blue light weighted radiance, LB , shall not exceed the levels defined by: where: L(λ,t) is the spectral radiance in W⋅m-2 ⋅sr-1 ⋅nm-1 , B(λ) is the blue-light hazard weighting function, ∆λ is the bandwidth in nm, t is the exposure duration in seconds.

Blue light hazard Retinal blue light hazard exposure limit - small source For a light source subtending an angle less than 0,011 radian the limits lead to a simpler equation. Thus the spectral irradiance at the eye Eλ , weighted against the blue-light hazard function B(λ) shall not exceed the levels defined by: where: Eλ (λ,t) is the spectral irradiance in W⋅m -2 ⋅nm -1 , B(λ) is the blue light hazard weighting function, ∆λ is the bandwidth in nm, t is the exposure duration in seconds. For a source where the blue light weighted irradiance, EB exceeds 0,01 W⋅m-2 , the maximum permissible exposure duration shall be computed: s, for t100 s tmax is the maximum permissible exposure duration in seconds, EB is the blue light hazard weighted irradiance.

Blue light hazard (B) and retinal burn (R) hazard spectrum

Retinal burn hazard Retinal thermal hazard exposure limit To protect against retinal thermal injury, the integrated spectral radiance of the light source, L λ , weighted by the burn hazard weighting function R(λ), i.e., the burn hazard weighted radiance, shall not exceed the levels defined by: where: Lλ is the spectral radiance in W⋅m-2 ⋅sr -1 nm -1 , R(λ) is the burn hazard weighting function, t is the viewing duration (or pulse duration if the lamp is pulsed), in seconds, ∆λ is the bandwidth in nm, α is the angular subtense of the source in radians.

„Physiological” radiance/irradiance and time average Radiance weighted according to the action spectrum 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 important!, 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 hazard groups Exempt group the lamp does not pose any photobiological hazard if it does not pose:• an actinic ultraviolet hazard (Es ) within 8-hours exposure (30000 s), nor a near-UV hazard (E UVA ) within 1000 s, (about 16 min) nor a retinal blue-light hazard (L B ) within 10000 s (about 2,8 h), nor a retinal thermal hazard (L R ) within 10 s, nor an infrared radiation hazard for the eye (E IR ) within 1000 s. Low risk group an actinic ultraviolet hazard (Es ) within 10000 s, nor a near ultraviolet hazard (EUVA ) within 300 s, nor a retinal blue-light hazard (L B ) within 100 s, ….

Emission limits for risk groups of continuous wave lamps

Lamp risk categories- acceptance angles Eye movement, time dependent smear effect taken into consideration

Differences betwen the CIE and IEC regulations

Lamp safety measurement conditions of Measurement distance: Minimum viewing distance: 200 mm GSL lamps: at a distance where it produces 500 lx 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

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, measured by the acceptance angle: g

Time dependence of acceptance angle to be used Due to eye movements 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: distance, where illuminace is 500 lx) Measurement aperture: maximum pupil size, 7 mm diameter Source size & angular subtense Thermal hazard source image size dependent: = 2 arctan(apparent source size/2 source distance) But amin=1.7mrad, amax=100 mrad 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 true weighted radiance of the source is needed, acceptance angle should not be smaller than 1.7 mrad. But LED assemblies with beam shaping optics have to be measured according to the standard. P-LEDs (and blue LEDs) might exceed the low-risk group

Example: p-LED, individual LED Blue light hazard exempt Low risk Moderte risk unit Accept. angle 100 11 1,7 mRad Limit, 104 4.106 W.m-2sr-1

LED-lamp based on LED component evaluation Risk group : low

White and coloured LEDs

Comparison: halogen incandescent lamp Risk group: low

Comparison: CFL

Comparison: MetalHalid Risk group: moderate

Effective blue light hazard radiance of different light sources allocation of conventional light sources as well as of retrofits LED in terms of their (dose-dependant) blue light hazard. Upper scale: effective B()-weighted radiance; lower scale: corresponding maximum duration for direct viewing from 200 mm distance (which define the particular RG-limits as indicated by the vertical lines)

Comparison of different light sources, relative action (equal luminance) aBL aL standard illuminant B (direct sunlight) 0.76 0.52 0.87 standard illuminant D65 (natural daylight) 0.94 0.68 1.06 standard illuminant A (incandescent Tc=2856K) 0.38 0.21 0.51 Halogen “HALOLUX” 0.37 0.2 0.5 CFL “DULUX” 0.47 0.36 0.62 standard Xenon 0.92 0.67 1.04 Fluorescence lamp “SKYWHITE” (Tc=8000 K) 0.98 0.75 1.09 Fluorescence lamp (Tc=14000 K) 1.23 1.0 1.35 „pc-white“ LED (Tc=3000 K) 0.34 0.45 „pc-white“ LED (Tc=5500 K) 0.74 0.8 „pc-white“ LED (Tc=6500 K) 0.81 0.6 0.9 Action spectra weighting: ac: circadian; aB: blue light; aL:lipofuscine-mediated age-related adverse effects

CIE S009/IEC62471 requirements, 1

CIE S009/IEC62471 requirements, 2

Thanks for your kind attention! This publication has been supported by the TÁMOP-4.2.2/B-10/1-2010-0025 project.