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Beyond Illumination
Evaluating the Non-Visual Emission
Characteristics of Lighting Products
Leslie Lyons
Technical Support Manager
Bentham Instruments Ltd
Optical Radiation
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Optical radiation is defined as electromagnetic radiation having wavelengths between 100nm to 1mm
Consideration typically restricted to 200-3000nm due to atmospheric absorption <200nm and the
negligible effect of low energy photons in the far IR
Band
Wavelength Range (nm)
UVC
100-280
(<180nm, vacuum UV)
UVB
280-315
UVA
315-400
Visible
380-780
IRA
780-1400
IRB
1400-3000
IRC
3000-10000
Lighting Products: Visual Characteristics
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We are all familiar with the visual characteristics of lighting products
Sources Having Non-Visual Impact
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We are also familiar with
sources of light having a
non-visual effect…
What Other Impact Might Lamps Have?
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It is therefore reasonable that lamps may also have other effects than visual…but what?
Photometric Flicker?
Circadian Disruption (or therapy)?
Photobiological Safety Hazards?
Photometric Flicker
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Recent reports have suggested that some SSL systems,
particularly those paired with dimming controls,
demonstrate significant photometric flicker
Photometric Flicker is defined as the cyclical variation in visual perception of a light source over time
thought to cause photosensitive epilepsy, migraines, headaches and non-specific malaise
Seizures thought to result from flicker in 3-70 Hz region, whilst “invisible” flicker effects may occur up
to 165 Hz
Flicker Metrics
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Two metrics are currently defined for the
evaluation of flicker: percent flicker, and flicker
index
The latter is generally preferred since it takes
account of difference in waveform shape or duty
cycle
As standards for the evaluation of flicker are
developed, account may also be taken of flicker
frequency
Measurement of Flicker
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Whilst flicker is a luminance-based property, one can use any input optic to perform this measurement
(telescope, cosine-corrected input optic, integrating sphere)
Light detection by close-match photometric detector, the output of which coupled to an amplifier and
data acquisition system fast enough to respond at least to 100 Hz
Time–resolved source emission captured, flicker calculations performed thereupon
Examples of Flicker
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Frequency (Hz)
Flicker
Percent (%)
Flicker Index
Halogen
100.13
CFL
100.1
GU10 LED 1
100.15
GU10 LED 2
100.18
4.96
1.13
1.36
8.4
0.016
0.004
0.003
0.026
Circadian Rhythm
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A circadian rhythm is a ~24 hour cycle in the physiological processes of living beings impacting sleepwake cycles, alertness, performance, core body temperature and the production of the hormones
Whilst endogenously generated, the circadian rhythm can be modulated, or entrained, by external
cues such as light and heat
Research has confirmed existence of melanopsin-based non-visual photoreceptor in eye having
inputs to circadian rhythm and pupil response
Whilst light stimulus at the “wrong” time may disrupt the circadian rhythm, light therapy could be
used for example to entrain the circadian rhythm of house-bound individuals
Circadian Disruption Metric
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Whilst most literature cites a 480nm peak response, the only published data in German DIN V 5031100 pre-standard suggests a 450nm peak
A metric, comparing the circadian response to visual response, is proposed
Evaluation of Circadian Disruption
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The spectral distribution of the source is required for this evaluation with subsequent evaluation
of acv
Incandescent
CFL
3000K White LED
10000K White LED
Blue LED
acv
0.046
0.102
0.043
0.493
0.541
Introduction to Photobiological Safety
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Photobiology is the study of the interaction of optical radiation with living
organisms
Optical radiation is strongly absorbed in tissue, with penetration depths of a
few microns in the UV to millimetres in the IR
It is the skin and eyes of the human body that are most at risk of exposure
IEC62471 Series Standards
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IEC62471-1:2006 “Photobiological Safety of Lamps and Lamp Systems”
- Gives guidance for evaluating the photobiological safety of lamps and lamp systems
emitting optical radiation in the range 200-3000nm
- Provides exposure limits and framework for classification including risk groups
exempt to RG3
- Intended as a horizontal standard
IEC TR 62471-2:2009 “Guidance on manufacturing requirements relating to non-laser
optical radiation safety”
- Provides further guidance in absence of vertical product standards
- Non-normative
IEC62471 published as EN62471:2008 and harmonised to low voltage directive (LVD)
Scope of IEC62471
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Consideration is given to six hazards to skin and eye:
Hazard
Wavelength
Range
(nm)
Bioeffect
Eye
Skin
Erythema
Elastosis
Actinic UV
200-400†
Near UV
315-400
Cornea - Photokeratitis
Conjunctiva - Conjunctivitis
Lens – Cataractogenesis
Lens – Cataractogenesis
Blue Light
300-700†
Retina – Photoretinitis
Retinal Thermal
380-1400†
Retina - Retinal burn
IR Radiation Eye
780-3000
Cornea - Corneal burn
Thermal Skin
380-3000
Skin burn
General Lighting Service lamp (GLS) sources used to illuminate “spaces”, measure at distance at
which source produces illuminance of 500 lux
All other sources measured at 200mm from (apparent) source
The Case of Lamps and Luminaires
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Implementation of GLS classification criterion of
IEC62471 has provided little satisfaction in the lighting
industry, prompting IEC sub-committee SC34A to take
action
Publication in 2012 of IEC TR 62778 : “Application of IEC
62471 for the assessment of blue light hazard to light
sources and luminaires”
Amendment of lamp and luminaire standards (many of
which have already been published) and updated under
the LVD
The New Lamp/ Luminaire Approach
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A consideration of photobiological safety depends on lamp type
In certain instances, consideration of UV hazard will remain, as
was hitherto the case, in implementing the 2mW/ klm specific
effective irradiance limit
IR hazard will be considered by one incandescent lamp vertical
standard
Blue light hazard will be dealt with, where required, in
implementation of IEC TR 62778
A Few Words on Blue Light Hazard
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Blue light hazard describes the photochemical damage of photoreceptors and the retinal pigmented
epithelium
Strong wavelength dependence, peaking in the blue spectral region (hence the name)
The evaluation of the retinal blue light hazard requires taking account of the irradiance of the retinal image
and the area of the retina irradiated for a given exposure time
Exposure time
IEC TR 62778
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Applies to the evaluation of component lamps/ LEDs to finished product luminaires
Evaluation to be performed at 200mm in an 11mrad FOV
Where result yields Exempt/ RG1 no further action required => Exempt / RG1 “Unlimited”
Where results yields RG2 (LB > 10000 W.m-2.sr-1), the distance at which source becomes RG1 should be
determined using the RG1 blue light small source limit of 1 W.m-2
Recommended Determination of dthr
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From spectral measurement of source 300-780nm, can determine ratio of illuminance/ luminance to blue
light irradiance/ radiance (numerically the same)
Determine illuminance, Ethr, at which blue light small source RG1 limit of 1 W.m-2 obtained
(= luminance (cd.m-2)/ blue light radiance (W.m-2.sr-1))
For component LEDs, report Ethr, for finished products determine dthr
The TR recommended method to determine dthr is to use goniophotometric data and the inverse square law
Luminance
(cd.m-2) )
1.55E+07
Blue Light Radiance
(W.m-2.sr-1)
19624.5
More Accurate Determination of dthr
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In many cases, use of the inverse square law is not valid since dthr is close to the source
As an alternative, an illuminance meter may be used to determine the location of dthr
For arrays, this procedure is incorrect since does not measure in the required 11mrad FOV resulting in
the determination of an overly-conservative dthr
Future Prospects
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As lamp and luminaire standards are harmonised to the LVD, IEC 62471 will no longer be applied directly
The implementation of standards on flicker and circadian disruption a long way off
Chronic low level exposure should be considered (for example, potential age-related macular
degeneration)
Lamp technology is still on the move with the use of UV rather than blue LEDs and even laser diodes to
pump phosphors- the impact of which is yet to be seen
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Thank You for Your Attention
Any Questions?