What is Color Rendering Index?
Color Rendering Index, or CRI, of a light bulb refers to how a specific light source makes the color of an object in the environment appear to a person and also how the subtle variations in its shades and hues are replicated. The CRI of a light source is expressed as a number on a scale ranging from 0 to 100. The higher this number, the better is the ability of the lighting source to render the color details of an object accurately, and as the eye ideally perceives color as it should be seen. Typically, great quality (and new energy efficient) lighting products should have a CRI of 70 or higher.
The following image illustrates the concept of CRI -
A distribution warehouse with old T12 and Metal Halide fixtures that have low CRI (60-65) - notice the bland and dull colors.
The same area after we retrofiitted it with new high 85 CRI T5HO fluorescent high bay fixtures - notice how the colors pop now!
You can see that by switching out old technology with new efficient lighting and boosting CRI by even 20 points can make a huge difference in color quality. The higher CRI allows for more clear and vibrant colors to be seen and allows indoor areas to look more like how they would appear outside in daylight, to mimic how the sun would make colors appear in our eyes. Knowing about the various aspects of CRI will help you choose the best quality and the most cost-efficient and appropriate lighting apparatus for your commercial and industrial premises.
Another way to think of it is like grading in school ranging from an A to F. CRI of 60 or below would be pretty bad like the first picture above or an F grade. At the other end, a CRI of 90+ would be an A grade, and make the colors very vibrant and accurate as the eye should see it.
How is CRI Measured?
In a nutshell, CRI of a specific light source can be figured out by comparing it to another light source that is considered perfect, or that has a 100 CRI. The sun or daylight has been traditionally used as the baseline standard to compare out different light source technologies with. It makes sense because the human eye is adapted best to see best with the sun shining.
To compare the CRI of two lighting sources, it is imperative that these two have the same color temperature. For the uninitiated, color temperature refers to the color of the light produced by different lighting sources. Different light bulbs cast differently-hued glows on the objects in an environment, ranging from the warm reddish tones produced by bulbs with lower color temperatures to the cool bluish-white colors emitted by bulbs with higher color temperatures. The color temperature of a light source is expressed in Kelvins (K).
What about different CRI and Color Temperature?
When buying light bulbs for your commercial space, you must keep in mind this relation between CRI and color temperature to ensure that you choose the right solution. The relation is explained with the following pictures comparing an old 400 watt high pressure sodium street light to a retrofit we did where a new 200 watt (56% energy savings) induction street light was installed.
The first picture above [left] is a 400 watt high pressure sodium street light that has a color temperature of around 2000K (very red-orange) and a CRI value of only 22. On top of using a lot of energy compared with today's standards, this is an example of old technology which has a low CRI and Kelvin Temperature. The low Kelvin temperature means that it puts out the orange/red color and the low CRI means the human eye won't pick up much of the color as it should be seen anyway. This is an old technology that puts out a lot of light (lumens) but compared with today's technology like fluorescent, LED, or induction, it doesn't really allow you to see things as they should be seen.
On the other hand, The second picture above shows the same streetlight that was changed out to an induction retrofit kit that mimics natural daylight and has a color temperature of 5000K (daylight white) and has a CRI value of 80-85. So the road is now lit with white light, along with a lot of it showing colors as you would see them in the daytime. Notice the pavement and grass color accuracy in particular.
On paper this is what the Kelvin Temperature range scale looks like. The 5000K daylight white induction lamp is indicated above, and you can see the 2000K range is very red-orange. For reference also - the Sun is 5780 Kelvin.
What is the CRI of Different Lighting Technologies?
Different light technologies go back decades and there have been vast improvements in both the same technologies and totally new ones. The incandescent bulb is ironically the oldest lighting technology out there, and also has a near perfect (95-100) CRI. as This is because the existing way of testing for CRI goes back a long time and uses a Black Body as the baseline, and an incandescent bulb is also a black body design, but it doesn't mean necessarily that this type of bulb emits a near-perfect color rendering as the eye is supposed to see things. There are new methods currently of making CRI more accurate but they have not officially been adopted yet. Here is a graph with the different technologies and their CRI:
|Low Pressure Sodium
|High Pressure Sodium
|Quartz Metal Halide
|Ceramic Metal Halide
Why do You need to Know about CRI when Considering a Lighting Retrofit?
More and more commercial space owners these days are choosing to replace the old high pressure sodium, metal halide, or T12 technologies in their work premises with more long-lasting, cost-efficient, and greener fluorescent, induction, or LED lights. Because CRI refers to the ability of light bulbs to accurately replicate colors, this value is an important parameter for building and business owners. But while retrofitting, you should know whether a light with a high CRI value is integral for your workspace or paying more for such a bulb will not enhance the productivity of your employees.
For instance, if you own an art gallery or work in a manufacturing facility that requires very specific specifications, you will need to install bulbs with CRI values greater than 90 in your workspace.
Similarly, light bulbs with CRI values between 80 and 90 are ideal for restaurants and textile manufacturing units. On the other hand, if your facility manufactures heavy industry equipment, light bulbs with CRI values between 60 and 70 will suffice because your workers need not be bothered about being able to see the exact colors of the machine parts they are dealing with. Bulbs with CRI values between 60 and 80 are also ideal for schools and offices where students and workers do not have to compare colors.
In general the latest technology in lighting has a 70+ CRI anyway, so if you don't have any specialized area, you can focus more on the energy efficient aspect and Kelvin temperature to adjust the lighting to your needs instead of such emphasis on CRI.
In short, when looking for lighting products, try to purchase the products with the highest CRI within your budget. Generally specialized products with 90+ CRI also mean they cost a bit more. But in some cases where you need very high color quality, this may be necessary. Whether it be standard LED, fluorescent, or induction energy efficient technology, they all are well developed and far along in that they all have pretty good CRI ratings (70+), and will light up your area as it should be seen in the daylight.
If you need help with your lighting project please email us or give us a call at 800.983.1315.