The following is a re-print of a publication by Terry McGowan of The American Lighting Association.
The Color Rendering Index and LED Light Sources
|Since the 1960s, there has been an internationally agreed-upon way to describe the color rendering of a light source using a simple numeric value. It’s called the Color Rendering Index, or CRI. It’s widely used and you will normally see it listed in lamp catalogs, specification sheets and on lamp cartons. Typical values of CRI for CFL and LED bulbs range from 80 to 90 and, more recently, CRI ratings over 90 have been appearing for LED products. Because the CRI attempts to rate the appearance of colors lighted by a specific light source, it must take into account the variety of colors used in interiors, from walls to furnishings and objects to complexion colors of people. The idea is to show, numerically, how people and things lighted with a high-CRI light source should appear more natural and normal than the same people and things lighted with a lower-CRI light source. And that means, for residential spaces, the higher the CRI, the better. That’s because the reference or “ideal” light source for visually warm residential spaces has been the incandescent lamp, which has a CRI of 100 by definition.A CRI rating of 100 is as good as it gets, this is because the CRI value represents a mathematical comparison of the measured color characteristics of a light source illuminating a defined set of color samples using a reference or “ideal” light source compared to the same measurements for the light source being evaluated. In other words, if all of the sample colors look the same under both light sources, that’s a 100% match and a CRI of 100. But, there’s an important caveat – the light sources being compared have to have the same or similar chromaticities for the CRI value to be meaningful. The chromaticity of a light source is a metric that describes the tint or tone of that source. For lamps typically sold to consumers and used in residential lighting, chromaticity is expressed in Kelvins or “K”. Incandescent lamps, for example, have chromaticities in the range of 2700 – 3000 K. On the DOE “lighting factsCM ” labels, which now appear on bulb cartons, that range is described as “Warm White”. Some incandescent lamps, such as the halogen-incandescent MR16 reflector types appear “whiter” because their chromaticities are designed to be at or slightly over 3000 K.However, there are problems with applying CRI values to LEDs. As LEDs began to be used for general lighting starting in about 2005, people noticed that what they saw with their eyes did not correspond with the CRI ratings. In some cases, colors illuminated with LED lighting looked better than the CRI values indicated; in other situations, the colors looked worse.The International Commission on Illumination (CIE), which wrote the CRI standard, has been aware of the problems and has now been working for several years to find an agreed-upon fix, with no success. In the interim, several new color rendering mathematical models have been proposed, including a metric called the Color Quality Scale or CQS, which was developed by the National Institute of Standards and Technology (NIST) in 2006. CQS addresses many of the problems with CRI, and several LED lighting manufacturers now report CQS ratings for their products, but CQS has not been adopted by the CIE, thus, the controversy continues.Last year, the Illuminating Engineering Society (IES) formed a Color Metric Test Group to develop an improved or complimentary color rendering index appropriate for LEDs. The IES reports that this work is in process; however, this past August, the IES said that the CRI “should not be used in energy regulations to characterize color attributes for solid state lighting until there is industry consensus on the issue.” The full IES statement can be viewed here. While the DOE and EPA/Energy Star have not yet commented on the IES statement, the California Energy Commission (CEC) heard testimony on September 29 proposing that the CEC ignore the IES statement for new Title 20 rules involving the regulation of small-diameter reflector lamps such as the LED versions of MR11 and MR16 products. The DOE, however, already recognized the problems early in 2008 via a technical bulletin “Color Rendering Index and LEDs,” which you can find here. It is brief and contains some helpful background information. So, considering that resolving the CRI issues and implementing a new metric have now already taken several years, and will likely take several more, should we continue to use the CRI just as we have been doing or is it time to make some changes? I recommend continuing to use the CRI, but also taking into account its limits, especially when dealing with LED lighting products. Here are a few practical suggestions that I hope you will find useful: -Consider the CRI an indicator rather than a measurement. At its best, CRI is an out-of-date, limited-use metric that tries to turn a complicated visual experience into a simple number. It’s useful, but not as precise as the CRI rating numbers suggest. -Differences in CRI values of 3-5 cannot usually be seen by normal eyes. -Currently, CRI values are calculated based upon a set of 8 or 15 color samples. See those color samples here: http://alturl.com/e6w64 (top row). Some lighting specifications call for the so-called “R9” value to be reported separately. That’s the color sample shown as TSC9 and sometimes described as “strong red.” -The color characteristics of LEDs are such that they can trick the CRI into reporting values that are misleading. -The color rendering values of an LED lighting product reported as CQS, rather than CRI, are more reliable. Both use the same 0-100 scale where higher is better. Note the color samples used for CQS (bottom row) are more saturated. -Expect to see some new and better metrics for evaluating the color rendering of light sources. One is called Gamut Area Index (GAI), but I’ll leave that subject for another column. -Human color vision is subjective, so the most reliable color rendering information is going to arrive via your eye. When other people are involved, say in a lighting showroom where products are being compared, nothing works better than an actual side-by-side color comparison in a full-scale demonstration. Check LED lamp and product manufacturers literature for interesting and clever ways to explain and describe the color characteristics of lighting products. There are some useful ideas out there. I recently gave a presentation on this subject at an LED lighting conference. That presentation can be downloaded from the ALA web site here. Your comments and questions are always welcome. Sincerely, Terry McGowan, FIES, LC Director of Engineering & Technology email@example.com|
There are three essential measurements to consider when locating a swing arm lamp. One is the height of the fixture in relationship to the height of the mattress the 2nd is the extension of the fixture and the 3rd is the adjustment in the shade. It is best to have the specification of the fixture and the bed size (including headboard/platform/frame) when placing the location of the j-box. The j-box is the power source and will determine exactly where the wiring is pulled through the wall. The fixture is then connected to the j-box. Each fixture will have an extension, typically between 18” and up to 29”. The extension determines the spacing between the edge of the mattress/frame and the j-box. I typically center the j-box with the center of the nightstand. Some platform beds can have a very wide frame style so the longer the extensions are very useful.
The best way to determine the height of the j-box is to sit on the mattress and measure from the floor to the top of your shoulder. For a standard frame this is typically between 44” and 46” of the floor. The bottom of the shade should be at your shoulder.
“What is color? No object of itself alone has color.
We know that even the most brightly colored object, if taken into total darkness, loses its color. Therefore, if an object is dependent upon light for color, color must be a property of light.
And so it is.”
Paul Outerbridge, Photographer 1896 – 1958
Have you ever wondered why things look different when you change a light bulb, say swapping a compact fluorescent for a good old incandescent? It is because the compact fluorescent has different color properties than the incandescent. The primary difference is know as color temperature.
For most common purposes color temperature is generally referred to as warm or cool, warm meaning more of the red spectrum in the light source and cool meaning more of the blue. Some scientists theorize that humans are pre-programmed to be more accepting of warmer color temperatures because our ancestors, for all the millennium, only experienced light from campfires and torches which is very warm light. This may or may not be true, but it is interesting to consider.
Of course preference for warm or cool light is a personal matter and varies among cultures around the world and even between areas in the United States. Residents of Northern climates tend to prefer warm light and residents of hotter ares lean toward cool. Here is another interesting fact: Sunlight changes its color as it crosses the sky. At dawn and sunset the sun appears more reddish, due to the filtering nature of the denser atmospheric layer it’s rays are passing thru at that angle. It has a correlated color temperature of approximately 2000°K at sunrise / sunset, and 5600°K when directly overhead.
Why is all the important to you? It is important because, for example, if you buy draperies for your house at a window treatment store they might not look the same in your house as they did in the store. Or, if you buy your draperies in your home at noon, they will not look the same at sunset. Just be aware the color is in the light, not in the surface from which that light is reflected.
For good, concise information and interactive examples of color and other light facts, consider downloading the Underwriter’s Laboratory app, LightSmart. Another good resource for lighting information is the American Lighting Association‘s web site. And, of course, please visit fogglighting.com to read our blog posts and learn how we might help you solve any lighting problem or challenge you may have.
Please be sure to think about floor lamps as you consider how to add light to your rooms. Floor lamps add interesting design elements and provide a pleasing layer of light.
In living rooms and family rooms you do not need a specific amount of illumination to perform tasks, you need layers of light to add interest and make the room feel inviting for friends and family.There are thousands of different styles of floor lamps from which to chose, something for every taste and situation.
Please visit FoggLighting.con for more useful suggestions. We are here to help if you need it.
Technical Explanation: The CRI is a unit that measures the ability of a light source to reproduce the colors of objects faithfully in comparison with an ideal source of light, or natural sources such as sunlight. The CRI is a determined value from 0 to 100, with 100 being the value “perfect” or daylight.
Real World Explanation: The CRI determines how you and your surroundings appear to you and the other people in your environment.
Looking at this photo, would you rather look like 50 or 100? Of course 100 is much more preferable. In our world of lights and lighting, the closest thing to the perfect value has traditionally been the good old incandescent light bulb. Now that regular incandescent light bulbs are impossible to find in most retail stores we are forced to find reasonable alternatives for our homes and offices. The alternatives to incandescent light bulbs have been compact fluorescent, CFL’s. CFL’s are now quickly being replaced with LED’s. All of these new light bulbs are not equal however. Some have high CRI values while others do not.
For example: I went to a new location of a coffee shop that I go to every now and then. The new location is being lit with LED track heads without much natural daylight. The old location is lit with regular fluorescent commercial style fixtures with lots of natural daylight. There is an employee who transferred from the old location to the new and it is astounding how differently that person looks under the LED illumination. The only reasonable explanation is that the CRI of the LED’s is really low. Skin tones, eyes, clothing…everything looks washed out.
Do not let that happen to you. You want to look good all the time. If you use low CRI light bulbs in your bathroom or dressing room, your make-up and clothing will look different outside in the daylight that it did when you got dressed and applied your make-up in your house. That is because of the poor color rendering of those light bulbs. All light bulbs now have labels that tell you the CRI. Best of all, good ones are not much more expensive than bad ones and using the good ones will enhance your appearance.
The Underwriter’s Laboratory app, LightSmart, has some really good information and examples of CRI and other useful lighting information. The American Lighting Association is another good resource to check out for lighting information. Please visit fogglighting.com for more useful information and please like us on Facebook.
Here is an example of what is happening in the the world of lighting today and what will continue to happen in the foreseeable future. LED’s are all the rage and designers are finding all sorts of new ways to incorporate them into light fixtures. The reasons are clear: LED’s consume far less energy than incandescent light bulbs, LED’s are cool to the touch, LED’s have better color temperature than they did in the past, LED’s have a super long life, and LED’s are small so fixture design can be very creative. In addition to LED fixtures like this one, LED light bulb design is evolving very quickly also. Technicians are finding ways to make them more attractive and more like the good old fashioned incandescent light bulbs. Some of the new LED light bulbs even grow warmer in color temperature as they are dimmed, just like incandescent light bulbs do. Additionally, new, more efficient heat sink materials are being developed which allow LED light bulbs be more streamlined and closer in appearance to both A-lamps and candelabra bulbs. Pretty soon you will be able to use LED bulbs in chandeliers and not notice a difference between them and the candelabra bulbs they replace. Best of all, LED’s are becoming less expensive all the time as manufacturing becomes more efficient and more manufacturers enter the marketplace. As with anything though, I urge you to be careful when buying any LED product as there still are huge quality differences among the myriad of products and producers out there. Try to see the product before you buy it to make sure the color of the light is acceptable to you. I recommend buying dimmable LED light bulbs and fixtures – some LED’s are not dimmable. I also recommend caution in using dedicated LED recessed lighting fixtures. Once you install them they are in the ceiling a long time and the quality of the light might not be satisfactory for you. Instead, consider buying a regular recessed fixture and using an LED light bulb. That way you are not locked in. Please visit our website www.fogglighting.com and like us on Facebook. You also might be interested in the Underwriter’s Laboratory app, LightSmart, which can be downloaded from the App Store. It has all kinds of great information about lighting…and its free.
Re-Printed From Residential Lighting Magazine November 2013 Issue
A Lighting Research Center study on lighting systems for Alzheimer’s patients could help an aging population.
Residential Lighting: Tell us how light levels affect circadian rhythms.
Mariana G. Figueiro, Ph.D.: Circadian rhythms are the rhythms in our body that repeat approximately every 24 hours. Light/dark patterns’ incident on the retina entrain our circadian rhythms to the 24-hour solar day. In the absence of this entraining stimuli, our circadian rhythms run with a period slightly greater than 24 hours. Light needed to activate the circadian rhythms is higher and “bluer” than that needed to activate the visual system. The circadian system is also looking for contrast between light and dark, so constant light or darkness is also not recommended. This might be what is happening with Alzheimer’s disease and related dementias (ADRD) patients, who tend to be in dim-light environments and constant-light environments. Increasing circadian light during the day and reducing it at night might be important for better sleep. We studied an elderly population with sleep disturbances and one with ADRD. In both cases, light helped them entrain to the solar day and be more awake during the day and sleep better at night. While the study is ongoing, preliminary results show that exposure to daytime light that is brighter than the ones found in assisted-living facilities and nursing homes and look more “bluish-white” than an incandescent light source, with less light exposure during the evening hours, can help ADRD patients sleep better at night and reduce agitation during the daytime hours.
RL: What kind of light is needed?
MF: Daylight is an ideal light source for the circadian system. A light source with a correlated color temperature of 6500K or higher would be ideal for daytime, along with light levels at the eye of at least 600 lux. In the evening, the use of warmer light sources, such as a 2700K with no more than 50 to 80 lux at the eye, is recommended. We also suggest a night lighting system that provides a low level of warm color, with horizontal/vertical cues to help with postural control to minimize falls. Lighting controls will play an important role because the daytime lighting system is different than the nighttime lighting system. In addition, personal sensors will become a key tool to allow for lighting schemes that promote entrainment at an individual level. Each person is different and responds to light differently. We need to be able to measure our circadian light/dark exposure and from that information design a lighting system that responds to our needs.
RL: Do LEDs and CFLs run counter to what Alzheimer’s patients need?
MF: Quite the contrary. These two light sources offer the possibility of using high correlated color temperature unlike incandescent lamps. Also, daylight can be energy-efficient and is a great light source for this application. In our study, we used GE Aquarium lamps that have a CCT of about 9200K.
RL: Is there more work to do?
MF: Yes. We have to start thinking about residential lighting that is coordinated with our work and school environments. In order to know when to add and remove circadian light to promote entrainment, we need to monitor our 24-hour light/dark exposures. In the case of older adults living in controlled environments, that task is easier. But for those of us who move from one building to another during the day, we need to monitor our light exposures and then have a system that can communicate with the sensors and feed information about the kind of lighting needed in the home. So the home environment will be a dynamic, individualized system that will respond to a person’s overall light exposures.
The following is a re-print of an ALA Technology Newsletter that was written by Terry McGowan at the ALA. It contains some interesting facts about current lighting usage and future trends.
- In U.S. residences, the average daily use per bulb is 1.6 hours.
- The average bulb uses 47.7 watts. (That’s down substantially from the 67 watt average reported in the 2002 report.)
- There are more than 67 bulbs in the average home considering all home types (single family, multi-family, etc.); but single family homes average more than 85 bulbs/home. (The average reported in the 2002 report was 37 bulbs/home.)
- Household lighting energy use varies substantially by region but averages
- 1,700 kWh/home per year. New York and California use the least averaging
- Less than 1,500 kWh while states including Montana, Wyoming, Arizona and Missouri used the most averaging over 2,100 kWh per home annually.
- The cost of energy used for residential lighting also varies by region, but total home lighting energy costs range from $200-300 per year.
- Bulbs in bedrooms, bathrooms, living rooms and kitchens consume the most lighting energy in the average home.
- Dimmers control only 4% of the bulbs in the average home and almost 80% of those bulbs are in ceiling fixtures.
- Incandescent bulbs (2010 data) remain the most widely used light source in homes (They are in more than 62% of the sockets); but the use of CFLs and LED bulbs has increased with CFLs at slightly more than 20% of the socketson average (also 2010 data).
- What the 2010-2012 report shows is that the conversion of residential sockets from standard incandescent to halogen incandescent, CFL or LED bulbs has rapidly increased over this last two-year period.
- Some of that increase is due, of course, to the phase-out of standard incandescent bulbs; but lower prices for CFL and LED bulbs, better bulb performance, more product choice and market activities such as rebates and the entry of new manufacturers into the market have all played a role as well.
- Of the “A-line” bulb sockets, 62% of the 3.2 billion in homes contained standard incandescent bulbs in 2010. That number has now dropped to 55%.
- But, LED bulbs, even though some 20 million have been installed over the last two years, still fill less than 1% of the total available sockets.
- The next two years, however, will likely see a dramatic change in those numbers because of the phase-out of the standard 40 watt and 60 watt bulbs beginning on January 1, 2014. Those two bulb types represent almost 60% of the standard bulb market.
Most lamps sold today have a label similar to the one pictured here.Why, might you ask, is there a fire risk if you use a higher watt light bulb than the one listed? The reason is because higher watts equates to higher temperatures. A watt is a unit of heat and is the amount of energy a light bulb uses. A watt is not to be confused with a lumen which is the measure of light output.
Lampshades confine a certain amount of heat depending on the diameter of the top opening. The smaller the opening, the smaller wattage light bulb should be used. Metal lampshades get hot themselves, sometimes too hot to touch. Sockets are made in lots of different quality levels and can get really hot also. The components of a light fixture all work together is a certain way. Whatever you do, pay attention to the label and use the proper incandescent light bulb.
All that being said however, CFL’s do not generate much heat at all so you can use a higher wattage equivalent CFL to produce more lumens than a lower wattage incandescent light bulb. For example, a 13 watt CFL produces about the same amount of light as a 75 watt incandescent light bulb so you could use it in a fixture that limits the watts to 40. Just don’t mess around with incandescent light bulbs, they can really be a fire hazard!
Download the UL app, LightSmart, from the app store for all kinds of lighting information and visit FoggLighting.com.