LED photobiology
János Schanda
University of Pannonia
Virtual Environment and Imaging Technologies
Laboratory
Overview
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Introduction
Optical radiation
LED emission spectra
 Human eye transmission
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Optical hazards
Conclusions and summary
Optical radiation - photobiology
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Ultra Violet radiation: actinic radiation
UV-A: 315 m – 400 nm
 UV-B: 280 nm – 315 nm
 UV-C: 100 nm – 280 nm
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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
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LED emission
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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
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Chemical – biochemical hazards
Photon energy in the range of energy of
chemical bonds
 Skin damages
 Ocular damages
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Thermal hazards
Skin damages
 Ocular damages
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Some photobiological hazard definitions
see CIE S 009:2002 Photobiological safety of lamps and lamp systems
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actinic dose (see ILV 845-06-23)
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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)
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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
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blue light hazard (BLH)
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erythema (see ILV 845-06-15)
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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.
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
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Distance from a source within which the radiance or irradiance for a
given exposure duration exceeds the applicable exposure limit.
Unit: m
Some photobiological hazard definitions
see CIE S 009:2002 Photobiological safety of lamps and lamp systems
 general lighting service (GLS) lamps
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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
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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
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retinal hazard region
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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).
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
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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
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Retinal blue light hazard exposure limit
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To protect against retinal photochemical injury from chronic bluelight 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 ,
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R(λ) is the burn hazard weighting function,
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t is the viewing duration (or pulse duration if the lamp is pulsed), in seconds,
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∆λ is the bandwidth in nm,
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α is the angular subtense of the source in radians.
„Physiological” radiance/irradiance and
time average
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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.
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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
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Lamp hazard groups
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Exempt group
the lamp does not pose any photobiological hazard if it
does not pose:•
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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
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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
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Eye movement, time dependent smear effect taken into
consideration
Differences betwen the CIE and IEC regulations
CIE/IEC comparison of the exemt limits
100000
w hite
IEC luminous intensity [cd]
10000
blue1
blue2
1000
verde
green1
100
green2
green3
10
yellow
orange
amber
1
red1
red2
0,1
x =y
0,01
0,01
0,1
1
10
100
1000
CIE lum inous intensity [cd]
10000
100000
Lamp safety
measurement conditions of
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Measurement distance:
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Minimum viewing distance: 200 mm
GSL lamps: at a distance where it produces 500 lx
Measurement aperture:
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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
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Due to eye movements for short durations small acceptance angles
have to be chosen
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FOV can be over- or under-filled
Product safety standard conditions
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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:
a = 2 arctan(apparent source size/2 source distance)
a But amin=1.7mrad, amax=100 mrad
a Apparent source position
Product safety issues
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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,
100
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 (dosedependant) 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)
Light source
aC
0.76
aBL
0.52
aL
0.87
standard illuminant B (direct sunlight)
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”
CFL “DULUX”
standard Xenon
0.37
0.47
0.92
Fluorescence lamp “SKYWHITE” (Tc=8000 K)
0.98
0.2
0.36
0.67
0.75
0.5
0.62
1.04
1.09
Fluorescence lamp (Tc=14000 K)
1.23
1.0
1.35
„pc-white“ LED (Tc=3000 K)
0.34
0.2
0.45
„pc-white“ LED (Tc=5500 K)
0.74
0.5
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.