Introduction to Color Rending Index (CRI) and Color Temperature
CRI or Color Rendering Index, Stoke’s shift, light temperature are words that manufacturers often use for promoting their different lighting products. Today, there is a war waging due to the Color Temperature and CRI in cyberspace for defending incandescent lamps against the ambush of energy-efficient LEDs and legislation.
- Do you know what all the jargon pertaining to light quality signifies?
- What does CRI mean and why people care about it?
- Is a CRI of 80 good or should you not settle for anything below 100?
- Is a CRI of 100 perfect?
- Are Color Rendering Index and Light Temperature related?
- Does LED lighting technology really impact parameters, such as CRI?
So, understanding such technical terms helps you in understanding the problems related to the light quality offered by CFLs, Bulbs, and LED devices. Only then, you can decide whether you should pay for a premium product having a nice Color Rendering Index (CRI).
Understand the Light Spectrum
Premium quality light is composed of various light colors. The multi-colored rainbow can be seen when the light gets split by tiny water droplets, which acts as prisms. The short version of different colors that constitute white light is “VIBGYOR”. With the help of a compact disc, you can make your own rainbow. On holding your disc towards the light, the CD’s prismatic layer splits up light into its fundamental colors. Thus, you see all of them constituting light.
The visible light colors are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. Out of all, the least energetic is Red and the most energetic is Violet. A spectrum even comprises of invisible light. As the names suggest, Ultra Violet derives after violet and Infra-Red derives before a red light.
An incredible light source, such as LEDs, emits full-spectrum light, featuring light with all the colors. Humans do not require UV or Infrared lights as one cannot see them through the eyes. In fact, these lights may damage paintings and art pieces in our homes.
There is a spectrum of IR, UV, and visible light radiation. It is just the spectrum’s colored portion that is significant for different lighting purposes. UV and IR lights can damage art objects as well as harm the skin. An incandescent bulb can produce 95% of the invisible infrared’s output range. Thus, making these bulbs extremely energy inefficient.
How do Humans See Colors?
White light comprises all the different light options in almost the same proportions. When the white light hits an object, most light colors are absorbed and only some are reflected. The object’s color is determined by the light color it reflects. Thus, it is significant that a source of light produces light with all light colors in it.
If the source light does not have a specific light color, then objects featuring that color cannot be seen in their original colors. That’s why a sodium light is worse at reproducing different colors. Sodium light falls under the category of a narrow-spectrum light. This light is primarily made of yellow light. When objects having different colors than yellow are kept under sodium light, they reflect just one color that is different yellow shades. Also, every object features a sickly hue. On contrary, LEDs produce original colors as they feature well-balanced light, containing an optimum spread of all the light colors.
Light Spectrum and Lighting Devices
An incandescent bulb produces warm yellow light that comprises light of all colors. However, this light is a bit poor in violet, blue, and green lights. Thus, when violet, blue, or green objects are observed under the light of an incandescent lamp, it does not reproduce these colors faithfully. On contrary, LEDs produce a well-balanced, complete spectrum of light, where natural colors of the object are reproduced.
- HID feature a CRI value of 72
- Mercury lights fall somewhere around CRI of 50
- Sodium lights feature a bad CRI around 25
- The CRI of LEDs and CFLs vary with light color but generally, it falls between 75 and 85
Thus, it is significant to note that a light source’s CRI is comparable across different sources that work at similar temperatures. As compared to incandescent bulbs, LED lighting functions even at low temperatures. Therefore, the CRI score of 85 underestimates their performance. Now, let’s have another take at the standard of CRI for reflecting the lighting world’s reality.
Color Rendering Index and Light Spectrum
CRI or Color Rendering Index refers to a measure of how light from a light source reproduces colors faithfully. For instance, incandescent lamps having a CRI around 100 is considered to be a perfect CRI score.
Thus, incandescent light is the perfect light source featuring the best CRI. This serves as a 100 index as the spectrum offers all wavelengths. One can compare incandescent light bulbs to the sun because the sun is a natural light source, having a CRI of 100. Normally, CFLs offer a CRI score of 80.
That’s the only reason that CFLs could not replace incandescent bulbs despite their heavy promotion. Also, there are CFLs producing warm light. However, for producing warm light, the CFL’s glass coating needs to be suitably doped with additives, which absorb light essentially in the spectrum’s one part and produce light in another part. This reduces the efficiency of CFLs.
LED systems and products fall under a different league. On observing images produced by LED projectors, the vibrant colors reproduced and their dominance over ancient incandescent technology seems apparent. LEDs come under superior light sources having good quality and lighting efficiency. When you search the history of lighting, you will find that the famous wide-spread and first electrical lamp has always been the incandescent one. The light sources that came after it, took advantage of new technology background and other possibilities of reproducing light. Every light source is different, which comes with its own advantages and disadvantages. It is quite obvious that earlier light sources will wipe out as others turn out to be better than the old technology. LEDs are the best light source that you can use now for various applications, including warehouses, schools, factories, and can even be used as LED Shop lights for lighting up workplaces.
Visual tests have proven that there is a need to review the CRI definition. In a study, scientists asked several observers to rate the color scheme used for defining the lamp’s CRI under various light sources. The comparison of LEDs with bulbs featuring a higher CRI has been surprising. The observers had the impression that both of these light sources would be equal in the light quality, although LEDs had a worse CRI per definition. So, there is a need to know that the CRI definition has been taken part within the period of the discharge lamp’s invention. Considering the CRI’s basis, this testing method has taken into consideration 14 varied standardized colors. However, only the first 8 colors of the color scheme are taken into the CRI calculation, surprisingly that are pale pastel colors. As you can see, the standard itself is under question. So, there is a need to modify the standards for reflecting the reality of the lighting technology of today.
What is Color Temperature?
The ‘color temperature’ term refers to the temperature of different objects through which they produce light, which is modeled through the “black body radiator”. On increasing the black body’s temperature, it begins to produce visible light in an incessant spectrum. In 60W incandescent lamps, the filament heats about 3000 degrees Fahrenheit. As a result, the lamps produce light with a 3000K color temperature. Many artificial light sources do not emit light through heating up of material until they glow like incandescent lamps. Instead of producing an incessant spectrum, they emit arrange of color emission lines. The color temperature of a black body cannot be given directly to this non-blackbody kind of emission, which is produced by high-intensity discharge, just in the case of fluorescent lamps.
What is Correlated Color Temperature?
A Correlated Color Temperature (CCT) is defined for a light source depending on its black body color temperature. For instance, a cool white fluorescent bulb features a CCT around 5000K. The light spectrum of lamps is different from the black body one. However, they have the same temperature.
The light color highly influences the surroundings. If you want a cozy ambiance, then go for a warm light color i.e. lower color temperature. Or else, go for a cool light source i.e. higher color temperature if you are looking for a more dynamic scene. The most significant factor is the CRI that you need to consider while selecting light sources. Also, check other factors like colors, contrasts, and faces. So, the CRI can be lower if the visual perception and task are easier. Only then, you need to examine the color temperature whether it supports the atmosphere of the space or not.
Comparison Table of the Reasonable Color Temperatures
|Lamp Color Name||Apparent Color Temperature (Kelvin)||Characteristics and Examples||Common Adjectives Used to Describe the Light||Best Location|
|Warm White||2700-3200K||Similar to incandescent bulb, yellowish light best for accentuating skin tones and color of wooden objects||Friendly, warm, inviting, intimate, relaxing||Homes, boutiques, reception areas, Hotels.|
|Natural White||4000-4500K||Similar to early morning sunlight, Xenon lamp for automotive use||Neat and clean, Natural tone||Offices, School Lights, Outdoor Areas|
|Day White||5500-6000K||Typical day light, Flash light. Metal Halide||Crisp light, efficient, brightly lit, natural outdoor||Retail stores, Factories, Printing, Warehouses, Schools, Parking Lots, Outdoor Area Lighting|
|Cool White||7000-7500K||Best contrast but least flattering to the skin, may need mixing with light from a warm white lamp.||Bright light, bluish light||Special applications needing high light intensity and good color rendition like art Galleries, museums, showcases for precious stones and jewelry|
What Role Does CRI Play in Buying Light Sources?
While buying light sources, you need to consider how much CRI you require. This depends entirely on your business, such as a retail store, a car dealership, a hospital, a warehouse, a factory, a school, or what. This is important because different facilities and businesses have different requirements and needs.
For instance, if you have a retail store that sells goods to customers, the CRI score around 80 is considered good. You can go for higher CRI like 85 or even 90 if you want. If not a retailer, then the CRI around 70 will work for you. However, you can vividly spot the difference between 90 CRI and 70 CRI if you know where to look at. If you have ever been to a lighting trade fair, you can make sense of what we are talking about.
When you walk into a booth displaying different glass bowls of flamboyant gumballs, you would not be able to spot the difference at first. Every bowl is placed under a LED and the CRI of that LED is labeled just above the bowl. On moving from the 70 CRI to the 95 CRI, you would not find any difference. This is because you do not know where you have to look. If you will look at the gumballs, especially red gumballs, then you will find that they look more vibrant and brighter when the CRI is increased. On contrary, other colors seemed quite the same from one bowl to the other.
So, as a warehouse or a factory manager, if you do not care whether the reds in the warehouse are not as brighter under 75 CRI than under 95 CRI, then you probably should not pay extra for that difference. However, if you have a clothing outlet, then you must be looking for the best light quality. In that case, you know what you need.
Comparing LED to Metal Halide and High Pressure Sodium
Considering many aspects, this is not actually a fair comparison. Especially, if you compare high-pressure sodium to every light source present out there today. This is because high-pressure sodium lights feature CRI around 20-40 and the color temperature falls around 2300K. So, all you get is a very warm yellow light that discolors everything around. You may have noticed how HPS lights make everything look yellow. This clearly indicates the poor CRI of such lights. So, good CRI tends to make colors appear as they are, whereas bad CRI discolors everything around. Comparatively, Metal Halide lamps are better. Their CRI is a lot better than the HPS one but lower than that of a LED. Thus, the quality of Metal Halide bulbs is not as fine as LEDs.
When you take a brand-new Metal Halide lamp out of the box, it is super bright. However, it begins to lose its lumens quickly. Within just 6months of usage, the lumens could drop by about 20% if you light it up for 12 hours per day. When the light remains 50%, it could lose around 50% of the original lumens, where its lifespan is of 15,000 hours. However, most people are not aware of this fact that Metal Halide bulbs lost their CRI effectiveness when lumens depreciate.
So, there is not just a decrease in the light quantity but also in the light quality. It is a double strike on the usefulness and amount of light. It seems that Metal Halide lamps are just fireworks, which are bright at the beginning and fizzle out rapidly. In the HID lighting world, it really makes complete sense to substitute these bulbs with LEDs because of the significant and dramatic savings present on converting over. Not just that, but also the light quality will dramatically enhance.
To conclude, the most significant thing that you have to remember regarding CRI is that you must consider the application that lights will be utilized for. Most installations do not require buying expensive high CRI lighting solutions. However, if the need comes, they are present for the applications that require making colors or products stand out.