Download RIN #27 VISIBLE LIGHT – NON

RIN #27
VISIBLE LIGHT – NON-LASER OPTICAL RADIATION
This radiation issue note addresses the exposure of the general public to visible light emitted by large outdoor
LED screens.
Exposure to Artificial Visible Light Emitted by Large
Outdoor LED Screens
Light emissions from natural and artificial sources include
ultraviolet (UV), visible (V) and infrared (IR) and cover the
wavelength range between 100 nanometers (nm) and 1
millimeter (mm) of the electromagnetic spectrum. The
corresponding frequency range is 3000 THz - 300 GHz.
The International Commission on Non Ionizing Radiation
Protection (ICNIRP) refers to light emissions as optical
radiation.
Table 1 Radiometric quantities and units
Size of the
light source
Point (small)
source
Extended
(large)
sources
1. Characteristics of Visible Light
Visible light is emitted in the wavelength range between
390 nm and 780 nm, as shown in Figure 1 below. It is
produced by different types of lamps (incandescent
lamps, electrical discharge lamps) and solid state light
devices such as light emitting diodes (LEDs).
Quantity
Symbol
SI Units
Irradiance
E
Watts per meter
squared [W/m2]
Radiant
exposure
H
Joules per meter
squared [J/m2]
Radiance
L
Watts per meter
squared per steradian
[W/ (m2.sr)]
Timeintegrated
radiance
Lp
Joules per meter
squared per steradian
[J/ (m2.sr)]
Photometric quantities describe relative brightness or
luminosity of the visible light to the human eye. Table 2
gives the photometric quantities and units used for
optical radiation.
Luminance is defined as the light brightness of a
source as perceived by the human eye.
Illuminance is the intensity of light falling on a
surface at normal incidence as perceived by the
human eye.
Table 2 Photometric quantities and units
Figure 1 the visible light spectrum
Quantity
Symbol
2. Quantities and Units Used for Optical Radiation
Luminance
Lv
Candela per meter squared (Cd/m2)
To measure the intensity of visible light, two sets of
quantities and units are used: radiometric and
photometric.
Illuminance
Ev
Lumen per meter squared [lm/m2 or Lux]
Radiometric quantities are physical quantities that are
used to describe the radiant energy of light, i.e. they are
related to the absolute measurement of optical
radiation. Exposure limits are expressed in terms of
radiometric quantities. Table 1 gives a summary of the
quantities and units used for optical radiation.
SI Units
3. Interaction of Non-Laser Visible Light with
Biological Tissue
3.1 Sensitivity of the eye to visible light
The human eye collects and focuses visible light.
Therefore, the retina is the part of the eye at greater
risk and needs to be protected.
(over)
For further information, please contact:
Radiation Protection | Environmental Health Services
th
LL0073, 655 12 Ave W | Vancouver BC V5Z 4R4
T: 604.707.2442 | F: 604.707.2441 | E: [email protected]
RIN #27
VISIBLE LIGHT – NON-LASER OPTICAL RADIATION
3.2 Mechanisms of interaction
The interaction of visible light with ocular tissue may
lead to no effect, thermal effects, or photochemical
effects, depending on the exposure levels and the
wavelengths of the optical emissions.
(a) No effects are expected when looking at a
visible light source emitting at low irradiance,
below the Exposure Limit Values (ELV).
(b) Temperature elevation (thermal effects) may
lead to thermal injury of the retina in case of
high irradiance and poor tissue heat cooling.
This effect could take place at all visible light
wavelengths, i.e. from 380 nm to 780 nm.
(c) “Blue light” Photochemical effects: Chemical
changes induced by bright lights at high
irradiance may lead to retinal photoretinitis and
this effect is more pronounced at the
wavelengths of blue light ranging from 435 nm
to 440 nm.
4. Exposure Value Limits (EVL) Applicable to Visible
Light
The International Commission on Non-ionizing
Radiation Protection uses a complex approach to define
the Exposure Value Limits (EVL). The EVL depend on
different exposure situations involving parameters such
as the size of the source, the subtended angle α (in
radians), the exposure time (in seconds), and the
wavelength range. See the ICNIRP reference below for
more details.
For the purpose of this RIN, we will take only the ICNIRP
Limit (Table 3) for the protection against blue light
photochemical retinal hazard within a wavelength range
of 380 nm to 700 nm:
Table 3 Exposure Value Limit for blue light
photochemical retinal hazard
Quantity
Exposure Value Limit (EVL)
Effective
Radiance L
100 W/(m .sr)
Assuming an exposure of 8 hours per day
2
According to ICNIRP, no assessment for retinal
hazard is necessary if the visible light has a
2
Luminance of less than 10,000 candela/m .
5. Measurement of Eye Exposure to Outdoor LED
Display Screens
The measurement of the exposure due to visible light
emitted by an outdoor LED billboard requires the use of
specific light-measuring devices with spectral analysis
capabilities (e.g. spectroradiometers). Special photometers
may be used to measure the Luminance at a distance
from the LED source in order to determine if radiation
assessment is necessary.
6. Public Exposure to Light Emitted by LED Display
Screens
The exposure of the population to optical emissions from
large outdoor LED screens is unlikely to reach the
Exposure Level Limit (EVL) recommended by ICNIRP.
Nevertheless, the measurement of visible light emitted
by large LED screens is recommended in situations where
radiation assessment is warranted in order to ensure the
safety of workers and/or members of the public.
ICNIRP Reference
Guidelines on limits of exposure to broad-band incoherent
optical radiation (0.38 to 3 μm), Health Physics Journal,
Vol. 73, #3, 1997.
Updated: Jan 2014