Lighting and the Visually Impaired

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Lighting
and the Visually Impaired
By Bryan Gerritsen,
Certified Low Vision Therapist
Copyright 2012
Including discussion of
different types of lighting
And with special emphasis
on LED Lighting
To begin, first a
question:
What is Light?
Light
is made up of
electromagnetic particles
that travel in waves.
Our retinas are capable of
responding to only a small part
of the entire
electromagnetic spectrum.
From the longest waves (lowest
frequency) through the shortest
waves (highest frequency),
lighting specialists identify the
electromagnetic wave regions as
1) radio waves, 2) microwaves
and radar, 3) millimeter waves
and telemetry, 4) infrared,
5) visible light, 6) ultraviolet,
and 7) x-rays and gamma rays.
Wave Lengths are measured
in “Nanometers”
Not all wavelengths are visible to
the human eye. For the most part,
this presentation will be limited to
visible light.
Definitions
• Nanometer (nm) is a measure of the
length of the light waves
• A nanometer is the extremely small
unit used to measure lengths of light
waves.
• One nanometer equals
• one billionth of a meter.
Definitions
• Correlated Color Temperature (CCT)
is a measurement of the actual color
appearance of light. It is expressed in
Kelvins (K). Low CCT numbers define
“warm” lighting like yellow and red hues
of candlelight at 1500K. High CCT
numbers define “cool” light, like blue
(5000K to 7000K).
Definitions
• Kelvin is the basic unit of
measurement for temperature
• The Kelvin temperature rating is
based on the color most highly
emitted
Definitions
• Footcandle (fc) and LUX (lx) are
units of illuminance, measuring
light on the surface
• 50 footcandle is generally considered
sufficient for many tasks
• Higher footcandles may be needed to
do fine work such as threading a
needle
Definitions
• Lumen (lm) is a measurement at the
light source (the lamp), and not
necessarily at the surface being lit
• It is the standard unit of luminous flux
(the time rate of flow of radiant
energy)
Definitions
• A watt is a unit of power equal to
work done, at the rate of one joule
• Wattage is actually a measurement
of energy, not of light
Ultraviolet Waves are very short
wave lengths of light that are not
visible to the Human Eye
•
•
•
•
UV-C are in the range of 100-290 nm
UV-B are in the range of 290-320 nm
UV-C are in the range of 320-400 nm
UV-B gets most of the blame for damaging
the eyes, skin, and materials
• UV light is to the left of visible light on the
light spectrum
Infrared Light
• Is also invisible to the human eye
• The term "Infra-" means "lower than”
• It has longer wavelengths than those
of the visible light spectrum
• It is to the right of visible light on the
light spectrum
Infrared Light
• Energy whose wavelength is too long to
see is "redder than red“ or Infrared.
• How do we know this kind of light exists?
• One way is that we can feel energy with
these wavelengths such as when we sit in
front of a campfire or when we get close to
a stove burner.
• Very long wavelengths of infrared light
radiate heat to outer space.
The visible light spectrum
ranges from about
400 nm (shortest)
to about 700 nm (longest)
The “visible light spectrum”
is that small part of the
electromagnetic wave
spectrum that we see
as colors.
From highest nanometers (700)
to the lowest (400), the colors
of visible light in order are:
•
•
•
•
•
•
•
Red
Orange
Yellow
Green
Blue
Indigo
And violet
The visible light spectrum is
shown in the diagram below.
Light is needed to trigger the
cone cells on the retina,
in order to read, to see details,
and to do all tasks
As we get older, we generally need
more light to read
and to do near tasks
• A German study stated that:
• A 50 year-old likely needs 10 times
as much light as a 10-year old to read
• A 65 year-old likely needs 15 times
as much light as a 10-year old to read
In addition,
the Need for Illumination
is much greater for a person
with a Vision Impairment
• They will likely need 3-4 times as
much light as a person their age, who
does not have a vision impairment
Specifically, persons with a
central field loss (such as AMD
or diabetic retinopathy)
• Will have damage to their cone cells
• Which are key in transmitting signals
of light received to the visual cortex of
the brain
• Therefore, they need improved
illumination for near tasks
The Need for Illumination
for Persons with Low Vision
• Is highest in persons with retinal
involvements such as
– AMD
– Stargardts
– Bests Disease
– Retinopathy of Prematurity
– Histoplasmosis
– Toxoplasmosis
The Need for Illumination
• Is also high for persons with:
– Optic Atrophy
– Retinitis Pigmentosa
– Glaucoma
– Cataracts
Research by Guinilla Portnoy, O.D.
and John Brabyn, Ph.D.
revealed that:
• An 85-year old person who has 20/40
visual acuity in a high brightness
setting and with normal or
high contrast materials
• Only has 20/200 visual acuity in a
poor brightness setting and with
low contrast materials
Many doctors or
low vision specialists
try to help that person
read more easily
merely with a magnifier
or with reading glasses
I’m certainly not saying or
suggesting that a magnifier or
reading glasses are not needed
or will not be helpful
for a person with 20/40
or 20/70 or any other
diminished visual acuity
But perhaps what is needed most
for that person,
or is as equally important
as a magnifier is:
• Illumination
• Illumination
• Illumination
How much light is needed?
Are there standards of how much
light is needed for specific tasks?
It is partially dependent on:
• The contrast of the item vs. its
background
• The size of the target being viewed
• The age of the person doing the task
• Whether the person has a visual
impairment and needs additional light
Lighting needs may also vary
according to:
•
•
•
•
Orientation (south vs. north facing room
Weather (cloudy vs. sunny day)
Time of day (position of the sun in the sky)
Season (position of the sun)
Different tasks and targets
also require varying
levels of illumination
• Reading items written in a #2 pencil, vs.
those written with a pen vs. those written
with a felt pen
• Reading items on a blackboard vs. those
on a whiteboard
• Seeing a ball in the gymnasium vs.
threading a needle ins the sewing room
Sample lighting standards for
different rooms or areas:
•
•
•
•
•
•
•
•
Bathroom
Cafeteria or snack bar
Kitchen
Classroom
Library or study area
Computer room
Clerical or secretarial areas
Shops or special labs
20 fc
20 fc
50 fc
45-55 fc
45-55 fc
40-70 fc
60-70 fc
50-100 fc
From Michigan Tech and Adopted from
Federal Energy Administration Guidelines
Lighting is dependent on the
contrast and the size of the target
Visual tasks with:
• High contrast and large size
30 fc
• High contrast and small size
50 fc
• Low contrast and small size
100 fc
• Extremely low contrast and
small size
300-1000 fc
Standards by the Illuminating and Engineering Society
of North America (IESNA)
These standards just given are for
people with “normal” vision
Please remember that
a person with a vision loss
may need about 3 times as
much light for near tasks as a
person with normal vision
The amount of light needed
for a person with a vision loss
for reading
Is closely related to their score
on a Contrast Sensitivity
Function (CSF) test
Persons with poor contrast
sensitivity function need very
bright illumination for reading
Persons with better contrast
sensitivity function (CSF) do not
need as much light for reading
Gerritsen and Christiansen, 2006
How do we Measure Light
in a Room or for a Task?
Lighting is measured
with a light meter
at 30 inches above the floor, at
various points in the room
A mathematical average
is then taken.
Light on a surface can be measured
with a Light Meter
in Footcandles (or Lux)
Measure the light for your students,
clients, or family member with a light
meter to help determine if lighting is
sufficient for the task they are
trying to do
The ratio of illumination in a room
• Should be approximately 5:3:1
• Between the page, the desk, and the
room
• This same ratio applies to a CCTV
screen, the working desk, and the
rest of the room
An important principle is not
just the amount of light, but
the position of the light
Therefore, it is important to talk
about something called the
“Inverse Square Law”
of lighting
Illumination Uses the
“Inverse Square Law”
That means that as a light source
gets closer, the amount of light
delivered is squared
Thus, if a lamp used to be
2 feet away
• And we move it closer so that now it is 1
foot away,
• It is not twice as bright, as we may
suppose;
• Instead, it is 4 times as bright, since we
square the amount of light delivered
Then if we bring it closer again,
moving it from 1 foot away
to 6 inches away
• We square the amount of light
delivered again
Perhaps the Best Way to
Make Use of the
“Inverse Square Law”
of Lighting
• Is to bring a lamp closer
Improved Illumination is not
So Much a Factor of the
Type of Light, or Even the
Wattage of Light Bulb
• Instead, it is mostly a factor of the
• Position of the light, using the
Inverse Square Law
We Can Bring a Lamp Closer
• By using a gooseneck or swing arm
–Desk lamp
–Floor lamp
–Clip-on lamp
There are many types of Light
•
•
•
•
•
•
Sunlight
Incandescent
Fluorescent
Halogen
Light Emitting Diodes or LED
“Daylight” or Full Spectrum
A lamp is not the fixture that holds
the light bulb or tube,
Nor is it a light
• A lamp is the light bulb or tube
itself which is contained in the fixture
• Light is the energy that emits from
the lamp
Types of Lamps—
Incandescent
Incandescent Lamps
• Contain a tungsten filament in a vacuum
• An electrical current causes the filament
to glow (incandesce)
Incandescent Lamps
•
•
•
•
Features a warm yellowish light
With little glare
Provides excellent contrast
Are very helpful for “task” lighting
They have a low Kelvin rating—
generally about
2700K to 3200K
Therefore they do not
emit any ultraviolet or “blue” light
Incandescent Lamps
• However they can be warm to work under
• They may have less even lighting and
more shadows than fluorescent lamps
• They generally cost more to operate than
fluorescent lamps
Incandescent Lamps may
Be on their Way Out
• Congress has passed laws that will likely
eliminate production of most incandescent
lamps by the year 2014
• However, incandescent lamps will
probably still be around for several years
after that, as will some replacement bulbs
• Incandescent lamps will continue to have
several strong advantages—e.g. high
contrast and minimal glare for the VI
Some specialty
incandescent bulbs
and lamps
will still be allowed and
produced after 2014
Types of Lamps—
Halogen
Halogen Lamps
• Contains a filament made of tungsten, so
it is a type of incandescent lamp
• However, it is different than a normal
incandescent lamp, because it also
contains the gas halogen
• Halogen recycles the burned particles of
tungsten, constantly rebuilding the filament
and giving it a longer life
Halogen Lamps
• Provide very bright illumination—perhaps
the brightest
• Have a “white” light appearance
They also have a low
Kelvin rating—
generally about
3700K to 3900K
Therefore they also do not
emit any ultraviolet or “blue” light
Halogen Lamps
• But by “pushing” the brightness the
contrast may be slightly diminished or
decreased
• They are very hot to work under and
dangerous to touch
• Because it is so hot, It can be a safety
hazard if not properly used
Types of Lamps—
Fluorescent
Fluorescent Lamps
• Is a phosphor-coated tube filled with
mercury and argon vapor
• An electrical current discharged into the
vapor causes the phosphor to glow
(fluoresce)
• The type and blend of phosphors used in
the coating determine the color of emitted
light
Fluorescent Lamps
•
•
•
•
Provides even lighting
With few shadows
Is cool to work under
May be a good choice for room lighting
They have a slightly higher
Kelvin rating—
generally about
4,200K to 4900K
Except for some models, they
generally do not emit ultraviolet light,
and do not emit “blue” light
Fluorescent Lamps
• May create glare for some persons
• May not provide as good contrast as
incandescent lamps
Types of Lamps—
“Full Spectrum”
Full Spectrum Lamps
• Are a type of fluorescent lamp
• Generally have a Correlated Color
Temperature (CCT) of 5,000K (Kelvin)
or higher
• And a Color Rendering Index (CRI)
of 90 or higher
• Often have enhanced levels of
Ultraviolet (UV) light
Full spectrum or “Daylight”
lamps generally have
a high Kelvin rating—
5,000K to 6,500K
They will emit both ultraviolet
and “blue” light
Full Spectrum or
“Daylight” Lamps
•
•
•
•
•
Mimic natural sunlight
May have the same phosphors as sunlight
Have an even light
Are cool to work under
Are excellent for color matching, quilting,
painting, art work, and hobbies
• May have applications in professional
settings such as dental work, for color
matching
Full Spectrum Lamps
• Often have “blue light” and may have
ultraviolet light (UV-A and UV-B)
• May have diminished contrast,
especially if over 5,000 K
• Therefore may not be the best for persons
with low vision, if they are concerned
about blue light and UV, or if they need
enhanced contrast
Types of Lamps—
LED’s
(Light Emitting Diodes)
LED Lamps
• Are a semiconductor device
• With a variety of phosphors, rare earth
elements, scintillators, or quantum dots
• Which produce electroluminescence
Colors of LED’s
• The color of emitted light depends on the
chemical composition of the semiconducting material used.
• It can be near-ultraviolet (NUV), visible or
infrared. The first practical visible spectrum
LED was produced in 1962. Red and
greens were available first, then blues in
1993.
• White LED’s became available in 1996.
LED Lamps
• May have a lower Kelvin rating of 2,700K
to 4,500K— “warm” white, OR
• A high Kelvin rating of 5,000K to 6,500K—
“cool” white or “daylight” white)
• Two LED lamps can be on the shelf next
to each other, look alike, cost the same,
and be made by the same manufacturer
• One may be rated as 3,200K, and the
other at 6,500K
A “warm” LED lamp will not emit
any UV or “blue” light
A “cool” LED lamp may
emit both UV and blue light
LED Lamps
• “Warm” LED’s may not be as bright as
“cool” or “daylight” LED’s
• However, they do not emit UV or “blue”
light like a “cool” LED may
• To compensate, you can choose a higher
output (lumens) lamp or position it closer
LED Lamps
• Are extremely energy efficient
• And can last an incredibly long time (up to
50,000 hours—perhaps several decades)
• Compare this to about 1,000 hours for an
incandescent bulb or 7,500 hours for a
compact fluorescent (CFL) bulb
• Thus, an LED lamp can last at least 4
times, and perhaps 7 times longer than a
compact fluorescent (CFL) bulb
When do LED Bulbs wear out?
• They don’t just burn out; instead they very
slowly become dimmer with age and use
• The Lighting Research Center (LRC)
defines useful life of LED lamps as the
point at which light output declines to 70%
of initial lumens
• Most manufacturers estimate a lifetime of
30,000 hours to the 70% lumen
maintenance level
As LED durability continues to
improve, some LED’s are rated
to last at this 70% level to
50,000 hours
If used an average of 3 hours a day,
this would mean a useful life of 27-46
years, allowing for the 30% lumen
depreciation
LED Lamps
• Are often more than a single diode—they
may have multiple diodes, a chip, or a
multi-chip, perhaps even several layers
• They may have a more narrow beam or
“spread” than other lamps
An important feature to
consider when choosing an
LED lamp is its “spread,” or
the width of the light beam
it produces
Try to select an LED lamp that
produces a fairly wide beam
of light
LED Bulbs
• Now come in an Edison (E-26 or E-27)
base, and will work in existing household
lamps and light fixtures, as direct screw-in
replacements (as little as $6 to $24)
LED Lamps
• Are increasingly taking over the market
formerly held by incandescent and
fluorescent lamps
• Because of their amazing longevity and
energy efficiency
• Also, they are encased in hard plastic
(rather than glass), so they don’t break,
and are shock resistant
• And, they do not contain mercury like CFL
bulbs (a problem when disposing of CFL’s)
LED Lamps
• Can even be battery operated, which
makes them very portable
Other LED Lights—
Headlamps, Flashlights,
and Stick-on Lights
LED lamps may be a
wonderful option for persons
with a vision loss
As table lamps, floor lamps, flashlights,
“stick-on” lights, and headlamps. Also,
remember that replacement bulbs are
now available in LED
In the future, organic LED’s
(OLED’s) may become available.
They create light on an ultra-thin
sheet. They could illuminate:
•
•
•
•
Ceiling tiles
Venetian blinds
TV screens and computer monitors
Mobile phones
“Blue light”
are short wave lengths on the
nanometer scale of visible light
• That range from about 400 nm
to 470 nm
• They are visible to the human eye
• And are perceived as the color blue
Laboratory studies on animals
seem nearly unanimous
that blue light causes
macular degeneration
However, real world studies on
people have produced conflicting
results
Blue light and
macular degeneration (AMD)
• Some studies positively link AMD with
any kind of light exposure
• Other studies have found a weak
correlation between AMD and blue light
exposure
• Yet a third group of studies has found no
correlation between AMD and sunlight
One Australian study concluded
that the problem is not total sun
exposure, but how sensitive you
are to the sun
This study also concluded that
people with blue irises are at
increased risk for AMD
People with blue or light-colored
eyes and fair skin may be
particularly susceptible to
macular damage from blue light
because they have less melanin
in their irises.
Melanin protects the macula by
trapping light rays so they don’t
reach the macula and
cause damage
In short, we probably cannot say
at this time that blue light
positively contributes
to macular degeneration
But the plausibility and
probability is certainly there
Therefore, because of a possible
link and possible benefit:
• Exposure to blue light should
possibly be limited
Also, “Blue blocker” sunglasses
should be worn
• Especially if you have blue or light colored
eyes and fair skin
• Or if you have other risk factors
• Or if you spend lots of time in bright
sunlight or on water, sand, or snow, which
reflects sunlight
• A sun visor or hat may also be helpful
The color that blocks blue is
yellow, so blue blockers must
contain a yellow tint
• This includes sunglasses and
glare shields with that are:
• Amber
• Orange
• Amber/orange
• Yellow and
• Plum
Problems with Some Lamps
Some lamps provide some
concerns, because they
may emit UV light and/or
blue light
Fluorescent Lamps
• In common fluorescent tubes, UV rays are
mostly blocked by the glass enclosure
• Blue light, however, may pass
through unimpeded
• Fluorescent tubes containing the older
halophospate type phosphors emit light
that is high in the blue spectrum
Full Spectrum Lamps
• Often contain the visible blue light
spectrum and the invisible UV light
• If they are rated with a CCT
(Correlated Color Temperature)
of 5,000K or higher (which almost all
do)
Full Spectrum Lamps rated at
5,000K or higher, and therefore
have blue and UV light include the
•
•
•
•
•
•
•
Ott Lite (5,000K)
Vita Lite (5,000K) and
Vital Lite Plus (5,500K)
Verilux Happy Eyes (5,500K)
UltraLux (5,500K)
VisionMax Full Spectrum (6,500K)
Sunlight Lamp by Bell & Howell (6,500K)
Other Full Spectrum Lamps
rated at 5,000K or higher
• “Bright as Day” by Sharper Image
(5,000K)
• PureLite (5,000K)
• BioPure Full Spectrum (5,500K)
• Life Lite by True Scan (5,500K)
• Paralite-Specra 5900 (5,900K)
• Balanced Spectrum (6,500K)
• Lumichrome (6,500K)
• Coil-Lite Compact Fluorescent (6,500K)
• And many others
LED Lamps
• Those rated over 5,000K contain blue light
• Care should be taken to ascertain the
Kelvin rating of LED lamps or bulbs, since
two could be made by the same
manufacturer and be sold alongside each
other on a shelf in a store, or on the same
page in a catalog. One could be rated
3,200K (“warm”), and the other 6,500K
(“cool”), and look almost exactly alike.
One author wrote, “Just as we
shield our skin from prolonged
sunlight, it makes sense that
we should also shield our
eyes when outdoors.”
He continues, “Until good
science provides more definite
answers, we might also be
wise to not bring the sun into
our houses and place it on
our desktops.”
However, even if we do not
accept research thus far about
any possible link between
blue light and retinal damage
(such as with macular
degeneration),
or completely put any
concern aside about
blue light . . .
Another important concern about
lamps with a CCT of
5,000K or more
• Is their diminished contrast
• As we push the brightness of a lamp,
we often sacrifice or diminish contrast
• Good contrast is generally very
important for a person who is visually
impaired
Finding lamps with a CCT
Correlated Color Temperature of
4,900K or less will help to
• Avoid having blue light and UV light
in the lamp
• Increase the contrast, which is so
important to a person with a vision
loss
Glare should be avoided
By carefully watching the
positioning of lighting
coming into the eye, and of
items being viewed
in relationship to light
sources
Note floor and table lamps, TV, and windows
Glare can also be minimized
by wearing glare shields
• Amber, amber/orange, orange, or plum
for bright or sunny days
• Yellow colored for indoors by a window,
for cloudy days, or for early morning or
late afternoon conditions
Bryan Gerritsen
CLVT
Low Vision Rehabilitation Services
(LVRS)
www.LowVisionRehabServices.com
[email protected]
Copyright
2012
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