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OLI-WP-01-20
SPECTRORADIOMETER WORKSTATION
FOR PHOTOBIOLOGICAL SAFETY STANDARD
IEC 62471 COMPLIANCE MEASUREMENTS
A White Paper by
Optronic Laboratories, Inc.
June 2020
1
Table of Contents
1.0 SUMMARY……………………………………….…………………………….………2
2.0 INTRODUCTION……………………………………………………………….………2
3.0 BACKGROUND…………………………………………..…………………….………3
LED Technology…………………………………………..…………………….………3
Photobiological Hazards (PBHs) of LEDs………………………….………………….3
4.0 DEVELOPMENT OF AN INTERNATIONAL PBH STANDARD………….………..5
Table 1: Summaries of IEC 62471 Technical Reports…………………………..……5
5.0 MAKING PHYSIOLOGICALLY RELEVANT PBH MEASUREMENTS……….…..6
Figure 1: Schematic of a Spectroradiometer Workstation .…………………..……..7
Table 2: Required Measurements of IEC 62471 Compliance...…………….………8
6.0 METRICS FOR DETERMINING EXPOSURE LIMITS……………….………..……8
7.0 RISK GROUP CLASSIFICATIONS………….…………………………………..……9
Table 3: Risk Group Categories…..…………………………………….………...……9
8.0 IEC 62471 SPECTRORADIOMETER WORKSTATION..…………….………..……9
OL 750-M-D Double Monochromator…...…………………………………...……….9
Radiance Module – OL 600 Direct Viewing Imaging Optics Module (DVIOM)…..10
Irradiance Module – OL IS-670 Integrating Sphere…...………………..…..……...10
Detection System – OL 750-HSD Hight Sensitivity Detectors…………..………..11
Validation and Compliance……………………………………….……….…………..11
Table 4: IEC 62471 Spectroradiometer Workstation..………………….……….…11
9.0 IEC 62471 COMPUTATIONS SUMMARY………………….…………..…………12
10.0 OL 750 MODULAR WORKSTATION…………………………………….…………13
Figure 2: OL 750 Modular Workstation Platforms…………………….……………13
11.0 PORTABLE SPECTRORADIOMETRIC STSTEMS……..………….………...……14
OL 756 Portable Double Monochromator………………………….………….……14
OL 770 CCD Spectroradiometer…………………………………………….…….…14
12.0 WORKS CITED…………………………………………………………………..……15
2
1.0 SUMMARY
In recent decades, advances in
materials science and technology have
substantially improved the quality of
lighting products. LEDs in particular
have become more rugged, with higher
efficiencies, greater stability, and emit
significantly higher optical power over a
wide range of spectral regions. As a
result, LEDs have found a place in many
aspects of day-to-day life. The growing
concern over the physical repercussions
of increasing human exposure has led
to the creation of an international
standard governing photobiological
hazard assessment of lamps and lamp
systems, IEC 62471 – Photobiological
Safety of Lamps and Lamp
Systems. The spectroradiometric
measurements needed for standard
compliance requires complex
instrumentation, not only for the third
party laboratories, but also LED
manufacturers in order to monitor these
optical properties throughout the
manufacturing process. Optronic
Laboratories, Inc. has developed an IEC
62471 workstation designed using our
modular OL 750 Series
Spectroradiometer that facilitates
straight forward assembly, seamless
measurement scans, and simple
transitions from one measurement
geometry to another. This paper will
describe the IEC 62471 standard and
discuss how the OL 750D IEC 62471
Spectroradiometric Workstation can
facilitate standard compliance for quality
control laboratories and LED
manufacturers alike.
2.0 INTRODUCTION
Historically, lasers and ultraviolet (UV)
lamps were the primary devices
requiring human safety analysis.
However, recent advances in
technology have resulted in light-
emitting diodes (LEDs) of superior
efficiencies and substantially higher
optical outputs, as well as operating at
wavelengths ranging from the UV,
through the visible and near infrared
(NIR), and into the shortwave infrared
(SWIR). These technological advances
have allowed LEDs to permeate most
aspects of daily life, but have also
brought into question the possible
hazards that result from increased
human exposure.
As international standards to assess the
photobiological compatibility of non-
laser lamps and lamp systems became
a reality, LED manufacturers faced new
and daunting responsibilities. While the
quality control laboratories faced
obtaining complex instrumentation
required for full standard compliance,
the manufacturers of LEDs and other
lighting components were now required
to both comprehend the standard
requirements as well as acquire the
3
ability to monitor the essential optical
parameters throughout the entire
manufacturing process.
This white paper aims to discuss the
necessity of an international standard on
photobiological safety, clarify the
various requirements of the standard,
and lay out the necessary
spectroradiometric measurements and
instrumentation necessary for full
compliance.
3.0 BACKGROUND
LEDs are semiconducting materials that
emit high-intensity optical radiation
across the UV, visible, and infrared (IR)
spectral regions. They have surpassed
the lighting industry standards in terms
of their efficiencies, lifetimes, and
optical output, resulting in their
ubiquitous presence in most aspects of
daily life. This increase exposure has
brought to the forefront a real concern
for the hazards that may result from
even incidental exposure to LED light.
LED Technology
The artificial lighting industry has long
been dominated by inefficient sources
of radiation such as incandescent and
fluorescent lamps. A review in 20161
estimated that the electrical lighting
industry accounts for 1/6th to 1/5th the
world’s energy consumption.
Incandescent lamps that depend on the
heating of a metal filament are
inherently inefficient, converting less
than 5% of the input energy to light.2
Compact fluorescent lamps (CFLs) use
up to 90% less energy and last up to 15
times longer than incandescent lamps3,
but are not a suitable long-term
replacement as they are toxic and not
environmentally friendly due to the use
of mercury vapor.4 In recent decades,
technical advances in electronics and
material science have allowed the use
of LEDs in residential and commercial
lighting to become more prevalent.
LEDs are much more energy efficient
than both incandescent and CFL lamps,
as well as last much longer.5
LEDs are composed of inorganic or
organic materials that emit light when
electricity flows through them. As a
result of continuing advancements in
their luminous efficacies1 as well as
LEDs that now emit light in the UV,
visible, and IR spectra, they are rapidly
infiltrating applications beyond lighting,
exposing more people to their
emission.6 Optical radiation, as defined
in the photobiological safety standards,
encompasses the wavelength range of
200nm to 3000nm, or UV, visible, near
infrared (NIR), and shortwave infrared
light.
4
Photobiological Hazards (PBHs)
of LEDs
As technological advancements allow
LEDs to be more efficient and more
powerful, the possible consequences of
human exposure to optical radiation,
both in the short-term as well as the
long-term, becomes of more concern.
The potential hazards of human
exposure are well known, particularly to
the skin and eye, and are classified into
two categories: photochemical or
thermal hazards. Photochemical hazards
occur when light of sufficient energy
breaks or rearranges the chemical
bonds in the cellular molecules. This
usually requires light of higher energy,
predominantly UV light. Thermal hazards
involve absorption of radiation,
particularly in the IR, in the form of heat.
This heat increases the temperature of
the surrounding area, which can have
devastating consequences for proteins
or other biochemical macromolecules
that are highly temperature sensitive.
Optical radiation from LEDs typically
affects the skin, the distal surfaces of
the eye, as well as the retina. The
specific hazards include:
• Photokeratitis – photochemical
reactions that induces chains of
biochemical reactions. Light in the
range of 200 – 400 nm causes this
with the peak sensitivity at 270
nm.
• Photoretinisis – often referred to
as “blue light hazards” is
photochemical damage, apparently
to the retinal pigment epithelium
from exposure to blue light,
primarily between 400 – 500 nm.
The peaks sensitivity is
approximately 445 nm.
• UV Cataractogenesis – clouding
of the lens due to prolonged
exposure to UVA light, primarily
from 290 – 325 nm, but possibly all
the way to 400nm. The peak action
is approximately 305 nm.
• IR Cataractogenesis – thermal
damage to the lens of the eye
caused primarily from 700 – 1400
nm, but possibly all the way out to
3000nm. Sometimes referred to as
“industrial heat cataract”,
“furnaceman’s cataract”, or
“glassblower’s cataract”.
• Retinal Thermal Injury – thermal
damage causing denaturing of
proteins and other key biochemical
components resulting in
destruction of the tissue. This is
caused by radiation in the range of
400 – 1400 nm, but peak
5
sensitivity is at 500 nm where the
human eye is most sensitive.
• Erythema – Reddening of the skin
(sunburn) due to exposure to UV
light, predominantly 200 – 320 nm
with a peak action around 290 nm.
Not all LEDs produce radiation that
results in photobiological or thermal
damage. The of the most concern are
those used for illumination and lighting
purposes. By the nature of this use,
long exposure times are likely.
4.0 DEVELOPMENT OF AN
INTERNATIONAL PBH
STANDARD
In the 1990s, LEDs were first evaluated
according to IEC 60825 – Safety of
Laser Products based on the existing
similarities between LEDs and lasers.
However, it is the differences between
the two that makes this an
unsatisfactory long-term solution. The
first attempt to separate LEDs from
lasers came when the Illuminating
Engineering Society of North America
(IESNA) created a standard that
encompassed LEDs as well as other
non-laser lamps and lamps systems
entitled RP-27, Recommended Practice
for Photobiological Safety for Lamps
and Lamp Systems: General
Requirements. The general
requirements in RP-27 were later used
by the International Commission on
Illumination (CIE) to develop an
international standard in the form of
standard CIE S 009/E:2002,
Photobiological Safety of Lamps and
Lamp Systems.
The work done by IESNA and CIE laid
the foundation for what would become
the current international standard on
PBH safety. The International
Electrotechnical Commission (IEC),
along with the IEEE (the world’s largest
technical professional organization)
developed a standard that is largely
based on IESNA RP-27, but also used
some of the updated information
regarding the relevant weighting
functions in CIE S 009, a standard that
became IEC 62471:2006,
Photobiological Safety of Lamps and
Lamp Systems.
Since the initial issuing of IEC 62471 in
2006, the IEC has subsequently
released technical reports to put forth
additional information and clarification
on a variety of subjects. Their contents
are summarized in Table 1.
6
5.0 MAKING
PHYSIOLOGICALLY
RELEVANT PBH
MEASUREMENTS One of the purposes of IEC 62471 was
to make standard a set of
measurements including suggestions
for the appropriate spectroradiometric
instrumentation. For the prescribed
measurements to be relevant to the
PBHs being considered, they must be
made in a manner that is consistent
with how the light impacts the body. All
of the PBHs assessed in IEC 62471 can
be classified into two categories, light
that strikes the superficial surfaces of
the body (skin, conjunctiva, cornea, and
lens) and light that enters the eye and
impinges on the retina. The two
spectroradiometric techniques needed
to best assess these phenomena are
irradiance and radiance measurements,
respectively.
• Irradiance – Irradiance is a
measure of the radiant flux (i.e. the
density of light) that impacts a
surface over a given area. This
measure is a good description of
how light coming from many
angles impacts a given area of
superficial surfaces (e.g. skin,
conjunctiva, cornea, and lens).
Irradiance measurements are
performed by collecting the light
using a cosine receptor, or an optic
capable of accepting light from a
180o field-of-view (FOV). This is
typically accomplished using an
integrating sphere. An integrating
sphere has an inner surface that is
coated with a highly reflective
material, typically PTFE or BaSO4 in
the visible and NIR to SWIR. The
light incident on the sphere’s
entrance port is collected from a
full 180o FOV, reflects within the
sphere several times, then exits
the sphere into spectroradiometer.
The spectroradiometer then
separates the collected light into
individual wavelengths, which is
then detected at the exit of the
spectrometer by an appropriate
detector. The schematic of a
spectroradiometer configured for
irradiance measurements is shown
in Fig. 1a:
7
• Radiance – Radiance is a measure
of the radiant flux (i.e. the density
of light) being emitted from a
source over a given area, in a well-
defined FOV, measured using the
3-dimensional angle units of
steradians (sr). The light that enters
the eye and impacts the retina is
determine by many physiological
aspects of the eye, namely the
diameter of the pupil (the aperture
of the eye that limits the light
entering the eye), and the ability of
the lens and other surfaces of the
eye to focus the light onto the
retina. The relevant FOVs used to
assess retinal hazards have been
determined based on these
parameters to be 0.0017 rad for
times shorter than the human blink
reflex (<0.25 s) or for pulsed
sources, 0.011 rad for times
between 10 and 100 s (rapid eye
movements spread the retinal
exposure), and 0.1 rad for times
exceeding 10,000 s (where typical
vision tasks spread the retinal
exposure even further). To achieve
Figure 1: a.) Schematic of a spectroradiometer configured for irradiance measurements with the IS-670 6”
integrating sphere on the entrance of the monochromator, followed by a 750-M-D double monochromator to disperse the light into individual wavelengths, and finally a high sensitivity detector on the exit of the
monochromator to quantify the collected light. b.) Schematic of a spectroradiometer configured for radiance
measurements with the OL 730-9 reflex telescope on the entrance of the monochromator, followed by a 750-M-D double monochromator to disperse the light into individual wavelengths, and finally a high
sensitivity detector to quantify the collected light.
8
these well-defined FOVs, a
telescope is typically used as the
collection optic for radiance
measurements. A telescope uses a
lens or mirror with a particular focal
length, which defines the distance
from the telescope to the light
source. Together with a limiting
aperture of known diameter, a very
well-defined FOV collects the light
to be analyzed by the
spectroradiometer (Fig. 1b).
A summary of all measurements
required for IEC 62471 as well as which
PBH they correspond to can be found in
Table 2.
6.0 METRICS FOR
DETERMINING EXPOSURE
LIMITS
The practicality of the IEC 62471:2006
standard lays in the exposure limits that
are defined for the described PBHs. For
the scope of this standard, the exposure
limit is defined as the maximum amount
of time a person can be continuously
exposed without adverse health effects.
They apply to all continuous sources
with durations not less than 0.01 ms
(i.e. non lasers) but not longer than an 8-
hour period, and pertain to average
people that do not suffer from
photosensitivity or other physiological
conditions causing them to be more
susceptible to PBHs. Each individual
exposure limit is defined based on the
spectral radiance or spectral irradiance
over the pertinent wavelength range
and takes into account the body’s
photosensitivity or response to the
wavelengths being analyzed. Once the
spectroradiometric measurements are
complete, it can be determined whether
an LED passes or fails each individual
PBH. For instance, when assessing the
blue-light hazard of an LED for exposure
time less than 104 s, the product of the
blue-light hazard weighted radiance and
the exposure time has to be at or below
106 J m-2 sr-1:
This equation can be rearranged and
solved for t (exposure time) in order to
determine the maximum permissible
exposure time for that particular LED
9
given its blue-light hazard weighted
radiance:
7.0 RISK GROUP
CLASSIFICATIONS
Once all spectroradiometric
measurements have been completed
and individual exposure limits
determined, the cumulative results can
then be used to assign a radiation
source to a corresponding risk group.
The risk group categories are meant to
communicate only the potential risk
associated with a source and the
general criteria are listed in Table 3.
8.0 IEC 62471
SPECTRORADIOMETER
WORKSTATION
To support IEC 62471 compliance
measurements, Optronic Laboratories,
Inc. has developed a complete
workstation that is based upon our
industry standard OL 750 double
monochromator, combined with
irradiance and radiance modules whose
performance is verified using NIST-
traceable performance verification
systems and standards. What follows is
a description of the system components
and which part(s) of the standard they
are applied to.
OL 750-M-D Double Monochromator
At the heart of the OL 750 platform
configured for IEC 62471:2006
compliance is the OL 750-M-D double
monochromator. Due to the accuracy
required at wavelengths down to
200nm where stray light can be a
significant source of error, the standard
suggests the use of a double
monochromator with superior stray light
rejection. To that end the OL 750-M-D
double monochromator has been
chosen, which has an industry-leading
stray light suppression of 10-8.
At the entrance of the OL 750-M-D is an
optical chopper with lock-in
amplification electronics. This system
helps to differentiate the analytical
10
signal of interest from any existing
background information, a technique
that is crucial in the UV and IR where
signal levels can be low and often
buried in the background signal.
The OL 750-M-D contains a pair of
identical grating turrets that holds up to
three gratings to facilitate seamless
scanning across the entire wavelength
range specified in IEC 62471. The
selected gratings are chosen to attain
the bandpass requirements over the
various wavelength regions using the
various slit configurations provided.
To further increase the reliability of the
measured signal, the OL 750-M-D
contains an 11-position filter wheel that
contains second-order blocking filters to
ensure the light being measured is only
that of interest and not a second-order
harmonic. The filter wheel also contains
a position that shutters the optical path
in order to obtain and accurate dark
current of the detectors and the
corresponding electronics.
Radiance Module - OL 600 Direct
Viewing Imaging Optics Module
(DVIOM)
The collection optics used to make
radiance-based measurements is the
OL 600 DVIOM, specifically configured
for IEC 62471 measurements. The OL
600 has a CCD remote imaging option
to see the telescope FOV in real-time,
as well the portion of the image that is
being spectrally analyzed. A circular
aperture wheel allows effortless
transitions between the various sized
apertures ranging in diameter from 0.3
to 5.0 mm. Accompanying the OL 600
DVIOM are two lenses custom
designed to achieve all of the FOV
requirements for the prescribed
radiance-based measurements. The OL
600 DVIOM can be coupled directly to
the entrance of the OL 750-M-D double
monochromator or via a fiber-optic cable
in order to allow increased
measurement flexibility.
Irradiance Module - OL IS-670
Integrating Sphere
The OL IS-670 is a 6” integrating sphere
that is internally coated with PTFE,
which has remarkable reflectivity over
the wavelength range of interest. The
standard requires that the device under
test be positioned at a distance that
produces an illuminance of 500 lux (but
not less than 200 mm). Therefore, the
sphere developed for IEC 62471 has a
built-in photometer that allows real-time
monitoring of the illuminance from the
source while positioning the device
under test. There is also a FOV adapter
accessory for the entrance port of the
OL IS-670 with apertures selected
provide an alternate method of making
some of the radiance-based
11
measurements.
Detection System - OL 750-HSD High
Sensitivity Detectors
A combination of three high sensitivity
detectors is provided to cover the entire
200 – 3000 nm range. The OL 750-HSD-
310 photomultiplier tube (PMT) provides
outstanding sensitivity in the UV. A
stable silicon detector (OL 750-HSD-
300) provides exceptional stability from
200 – 1100 nm. A thermoelectrically-
cooled PbS detector (OL 750-HSD-340)
overlaps with the top end of the Si
detector’s range and extends out to
3200 nm, completely encompassing the
prescribed wavelength range. There is
an automated detector selector
available that allows all three detectors
to be connecting permitting seamless
scans from one detector to another over
the complete range.
Validation and Compliance
When a spectroradiometer is calibrated,
it is calibrated as an entire system –
meaning the collection optics, the
monochromator, the detector, and all
elements along the optical path. Not
only does IEC 62471 require two
different spectroradiometric
measurement techniques, but it also
requires multiple measurement
geometries within each technique.
Therefore, we offer NIST-traceable
calibration standards and accessories to
facilitate in-house system response
calibration when the platform is
converted from one technique to
another, or the measurement geometry
is altered.
Full system specifications are compiled
in Table 4.
12
9.0 IEC 62471 COMPUTATIONS SUMMARY
1. With a 1200 groove/mm grating
2. Narrower bandwidths obtainable with optional smaller slits 3. Listed respective to aperture sizes
4. Actual size specified at time of order
13
10.0 OL 750 MODULAR
WORKSTATION
The versatility of the OL 750 platform
comes from its modularity. The system
can be easily converted from one
application to another by adding new
accessories or components. Instead of
using a collection optic on the entrance
port of the OL 750 monochromator, our
OL 740-20 or OL 750-20 light sources
can be used to provide a
monochromatic light source as in Fig.
2a-d. The source is configurable with a
deuterium lamp, quartz-tungsten
halogen lamp, and/or IR glower to
produce radiation from 200 nm out to
40 µm. Our collimating optics (either
750-10C shown in Fig. 2a and 2b
or the OL 750-11C) attached to the exit
port of the monochromator allows the
OL 750 to be utilized as a collimated
light source (Fig. 2b), for transmittance
measurements (Fig. 2a), or detector
spectral power/irradiance response
measurements. A wide selection of
accessories for the exit port of the
monochromator also allow the OL 750
spectroradiometric system to be
configured for spectral and/or diffuse
reflectance and transmittance
measurements as well as
internal/external/total quantum
efficiency measurements of detectors
and solar cells.
Figure 2: OL 750 Modular Workstation Platforms a.) OL 750 spectroradiometric system configured for total transmittance measurements. b.) OL 750 spectroradiometric system configured as a collimated monochromatic light source. c.) OL 750 spectroradiometric system configured for diffuse/total reflectance and/or transmittance measurements. d.) 750 spectroradiometric system configured for goniometric specular reflectance measurements.
14
11.0 PORTABLE
SPECTRORADIOMETRIC
SYSTEMS
Optronic Laboratories, Inc. offers two
alternative spectroradiometric platforms
whose small spatial footprints allow
versatile portability for a variety of
applications. These two platforms are
the OL 756 UV/VIS scanning double
monochromator spectroradiometer and
the OL 770 CCD multichannel
spectroradiometer.
OL 756 Portable Double
Monochromator
The OL 756 spectroradiometer is a
scanning double monochromator with a
TE-cooled photomultiplier tube (PMT)
detector with a spectral range from 200
– 800 nm. The dynamic range spans
seven decades with outstanding stray
light rejection of < 10-8 at 285 nm. The
OL 756 is designed for irradiance
measurements of solar radiation and
solar simulators. Its small footprint, light
weight (25 lbs) and quick scan speed
(up to 200 nm/s in quick scan mode)
make the OL 756 uniquely suited for
measurements in the field. A rugged
carrying case designed specifically for
the OL 756 is available to facilitate
transport without compromising
performance.
OL 770 CCD Spectroradiometer
The OL 770 series multichannel CCD
spectroradiometer is a modular system
with a myriad of collection accessories
to be configured for various
measurement types. The OL 770 has an
incredibly small footprint, is light weight
(22.5 lbs), and provides high-precision,
fast, and accurate research-grade
measurements over wavelength ranges
spanning from the UV to the NIR.
Optional accessories allow the OL 770
series spectroradiometric platform to be
configured for applications including
spectral radiance, spectral irradiance,
LED measurements, display testing,
on-line production testing,
reflectance/transmittances
measurements, goniometric
measurements, and NVIS compliance.
15
12.0 WORKS CITED
1. Zissis G. (2016) Energy Consumption and Environmental and Economic Impact of Lighting: The Current Situation. In: Karlicek R., Sun CC., Zissis G., Ma R. (eds) Handbook of Advanced Lighting Technology. Springer, Cham
2. Keefe, T.J. (2007). "The Nature of Light". Archived from the original on 23 April 2012. Retrieved 15 June 2020.
3. "Compact Fluorescent Light Bulbs". Energy Star. Retrieved 15 June 2020.
4. Beth Daley, “Mercury leaks found as new bulbs break: Energy benefits of fluorescents may outweigh risk,” The Boston Globe, February 26, 2008.
5. Pinto, R.A., Cosetin, M.R., Marchesan, T.B., Da Silva, M.F., Denardin, G.W., Fraytag, J., Campos, A. and Do Prado, R.N., “Design procedure for a compact lamp using high-intensity LEDs,” 35th Annual Conference of IEEE Industrial Electronics, pp. 3506-3511, 2009.
6. Opel, D.R., Hagstrom, E., Pace, A.K., Sisto, K., Hirano-Ali, S.A., Desai, S. Swan, J. “Light-emitting Diodes: A Brief Review and Clinical Experience.” J Clin Aesthet Dermatol. 2015 Jun; 8(6): 36–44