With LEDs (Light Emitting Diodes) becoming more prevalent in our everyday lives, it can be difficult to understand the different ratings on LEDs and select the correct one for your application. Let’s review some of these ratings and how they can affect your LED light selection.
The human eye is very complex and can detect a wide range of colors, even though the band or wavelength of light that the human eye can see (visible light) is very narrow. The range the human eye can see runs from 380 to 780 Nanometers. 380 Nm appears very purple in color to us, and 780 Nm is deep red. Dropping just out of our visible range at the low end is Ultra -Violet waves, and Infra-Red at the high end. The reason that this range can be important to you is because some LEDs can produce light within the ranges that your brain will not process and adjust your eyes accordingly. This can be dangerous to your vision in both the IR and UV ranges.
The 780 Nm and above range is where many security cameras will operate after dark using IR emitting LEDs. This allows the camera that has a wider band width than our eye can work in the dark. Night vision equipment would need to be used for the human eye to see in this same wave range, and the device would bring the IR wavelength back into our visible range.
There are several ways that LEDs are rated. The most common ratings used when describing an LED is Lumens, Candela or Peak Beam Intensity, Kelvin, and CRI. Some of these measurements are used for both LEDs and Incandescent bulbs, and some focus more on solely LEDs. Lumens is the measurement of the brightness or output of either an LED or a light bulb. It does not take into consideration the other factors that could affect the output such as tinted bulb shaped covers, reflectors, lenses, optics, etc. This measurement is measured most often in an integrating sphere that would measure the total output of just the bulb or LED.
Candela or Peak Beam Intensity is a measurement of the brightest part of the beam that is emitted from the LED or a bulb. This measurement is taken at a distance from the light’s source (ANSI standard is 100 feet). This measurement considers all the factors of the other components that could affect the beam and output. The measurement is taken with a light sensor mounted 100’ away from the light. It translates back to the machine in foot candles and this can then be calculated into Candela or Peak Beam Intensity. There are positives and negatives to this rating primarily based on what your application requires.
For example, if you are using this in a flashlight measurement it would be very accurate and helpful. The flashlight with a Candela rating of 200 would have twice as much light on your target at 100 feet as compared to the same light with a 100 Candela rating. If you are searching for LED replacement bulbs for your house, this rating would not be helpful. Lumens would be of more importance to determine bulb selection.
All incandescent bulbs or LEDs can be measured on the Kelvin scale. This scale runs from 1500 degrees Kelvin (about the color of a candle) up to 9000 degrees Kelvin (the same amount of light from a bright blue sky). The scale shows a warm yellow tone up to a cool blue tone. The higher the degree of Kelvin, the whiter and brighter the light will appear. Kelvin is a scale that describes different color characteristics of light, which can also be referred to as color temperature. The Kelvin rating is an important factor in almost any type of application. Most people would not want a bright white, high Kelvin rated light for reading or in a living room, but you might want that high color temperature for your workshop, garage, or a flashlight application.
Another rating scale that is emerging into many new markets is called CRI (Color Rendering Index). The basic concepts of CRI were developed in 1931, and have had many updates, including new measurements developed with the emergence of LEDs. CRI measures the ability of a light source to accurately reproduce the color of an object that it is illuminating. The CRI scale runs from 0 to 100 with bright, outdoor sunlight earning a perfect score of 100. Most incandescent bulbs with Tungsten type filaments also score 100 (one of the few instances in which incandescent bulbs perform better than LEDs). On the CRI scale a 90 or above is considered excellent, while 80 and below is considered poor.
CRI can be used to measure both natural light sources and artificial light sources such as LEDs and Fluorescent lamps. Compact, fluorescent lights score in the 50 CRI range, with 80 CRI as the standard range, and 90 and above considered high CRI. The CRI would not be visible until the light was shined onto an object and reflected back to the eye off that object. With lower CRI ratings your eye will not perceive colors or details as well when viewing the lighted object or objects. Low CRI can also affect the object/objects by making them appear in the wrong or incorrect colors because the best CRI color wavelengths your eye can see are not being projected onto the object.
Different types of light sources will have different color wave lengths that are enhanced. High CRI is a higher balance of the true color of the object to your eye. For example, you are selecting paint colors at your local paint store (fluorescent store lighting). When you leave the store and proceed home to paint, the color you chose looks very different on your walls than what it did when you looked at it in the store. The reason the color looks different in your home is because of the lighting sources. You might have natural light pouring into the room through your windows, or incandescent bulbs in your lamps or fixtures that are providing high CRI light in the room. The CRI was not high at the store because of the fluorescent lights, which in turn enhanced only the greens and orange tones of the paint color to your eye. This is the CRI characteristic of fluorescent bulbs.
CRI is critical in the camera and photography markets as it is ideal to achieve bright, vivid color and the detail of an object. CRI is also becoming a component in flashlights and other lighting products for use in vehicle paint matching, deciphering electrical and phone wiring, and where correct color identification is critical. Two different lights can produce the same Lumen output and Kelvin ratings but have different CRI numbers and make the same room or object appear differently to your eye.
When selecting your LED or Incandescent bulbs, keep in mind the application and the most important criteria. Do you require output in Lumens or Candela, color temperature measured in Kelvin degrees, or the CRI that you will be requiring. Almost all LED replacement bulbs will have many of these ratings listed on the side of the packages, so you can review them before purchasing. We hope this information will assist you with your next lighting purchase.