Presentation on theme: "Lighting and the Visually Impaired By Bryan Gerritsen, Certified Low Vision Therapist Copyright 2012."— Presentation transcript:
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.
Red Orange Yellow Green Blue Indigo And violet From highest nanometers (700) to the lowest (400), the colors of visible light in order are:
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
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: Bathroom20 fc Cafeteria or snack bar20 fc Kitchen50 fc Classroom45-55 fc Library or study area45-55 fc Computer room40-70 fc Clerical or secretarial areas60-70 fc Shops or special labs50-100 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 size30 fc High contrast and small size50 fc Low contrast and small size100 fc Extremely low contrast and small size300-1000 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 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 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