Lighting and the Visually Impaired

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Transcript Lighting and the Visually Impaired

Lighting

and the Visually Impaired

Bryan Gerritsen

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) length

is a measure of the 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 UV-B UV-C

are in the range of are in the range of are in the range of

100-290 nm 290-320 nm 320-400 nm UV-B

gets most of the blame for damaging the eyes, skin, and materials •

UV light

is to the

left

light spectrum of visible light on the

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 a s c o l o r s .

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 threading a

needle gymnasium

ins the vs.

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 High contrast and small size Low contrast and small size Extremely low contrast and small size 30 fc 50 fc 100 fc 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

suppose; as bright, as we may • Instead, it is

4 times square

as bright, since we 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

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

or higher • Often have

enhanced levels 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 semi conducting 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

yellow

, so blue blockers must contain a

yellow

tint • • • • • • This includes sunglasses and glare shields with that are:

Amber Orange Amber/orange Yellow Plum

and

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

mostly blocked by the glass enclosure are •

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”

(5,000K) by Sharper Image

PureLite BioPure

(5,000K) Full Spectrum (5,500K)

Life Lite

by True Scan (5,500K)

Paralite-Specra 5900 Balanced Spectrum

(5,900K) (6,500K)

Lumichrome

(6,500K)

Coil-Lite Compact Fluorescent And many others

(6,500K)

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