The best lighting products offer both color and lumen output stability. However, all light sources (even LEDs) will inevitably lose color and lumen output over years. Depending on the product, the user may not notice these changes because they become accustomed to the slow, gradual change in normal light levels and color in the space. However, with many products, this shift in color is very noticeable and can be a major problem.
The LED industry has always been focused on improving efficiency by producing more light out of less wattage. However, more recently, professionals in the industry have noticed a need to address the issue of color maintenance overtime, or, color stability.
It's important to note that color stability and color consistency are different. Color stability is a product's ability to maintain constant color (chromaticity) over time, whereas color consistency refers to product-to-product variation in chromaticity among a batch of supposedly identical lamps or fixtures from a given manufacturer. When we discuss color shift, color stability is the key.
Color stability is the ability of a light source to maintain its color properties over time, and it can be a critical (yet overlooked) quality of a lighting product. Color properties of lamps and fixtures may change over their lifetime, even if they are manufactured with consistent correlated color temperatures (CCTs).
The color of light produced from a light source will correspond to the wavelength of the energy radiated. Temperature is closely related to the visible aspect of the electromagnetic spectrum, which is why we refer to a light source as having a color temperature. An incandescent lamp produces a warm, white color, which leans more towards the yellow orange end of the light spectrum. A metal halide lamp is higher in the color spectrum and produces a cooler white that leans more towards the blue end of the light spectrum.
Color stability varies from product to product and manufacturer to manufacturer. It is something that should be included in the specifications or warranty language of a given product.
Have you ever been in a parking lot and noticed several pole lights that each emit a slightly different color? This is caused by color shift. Color shift occurs when there is a significant change in the spectral output of a light source, which results in a change in a light source’s CCT (Correlated Color Temperature) and color rendering (CRI) properties over their operational life. In short, color shift is a gradual (or dramatic in the case of poor quality lamps and fixtures) change in the color of light emitted from a light source.
The range of color shift that a manufacturer states may occur within a lamp or fixture’s warranty period. It is something that should be proactively addressed by a manufacturer within a products specification documentation.
Many factors affect the light quality of LEDs. Color temperature (CCT), color rendition (CRI) and color quality all affect how light works and how it is perceived. Actual color temperature can vary from one manufacturer to another even if they report the same measurement. In addition, the color temperature of an LED can change over time (Color Shift), which means the value after few thousand hours of use may not be the same as that for a new product.
(Technical information incoming!) The MacAdam Ellipses is an elliptical region on the CIE chromaticity diagram that contains all the colors that are indistinguishable to the average human eye. The MacAdams System ranks color quality on a scale of 0 to 10 and provides a guideline as to how accurate an average person’s color vision is, and how good they are at distinguishing between similar colors. This system is also used to refine the binning process of LED colors, meaning that slight color differences in LEDs are measured in MacAdam ellipses or steps.
MacAdams Requirements are shown below:
MacAdam 1–3 SDCM
Macadam 2 SDCM: museum, gallery applications
Macadam 3 SDCM: office, school, retail, healthcare applications
MacAdam 4–6 SDCM
Macadam 3 SDCM: outdoor facades
Macadam 5 SDCM: other outdoor applications
To prevent inconsistent colors, LEDs are sorted and grouped in batches known as “chromaticity bins.” The number of ellipses that the LEDs fall into is a metric to express the extent of color differences within a batch (bin) of LEDs. Macadams Ellipses relate to how LEDs with certain manufacturer sorted bins can be purchased.
Manufacturers of LED Diodes (who are often not the same companies that make the final products such as lamps and fixtures) sort their products into ‘bins’ according to performance. The fewer bins your LEDs are selected from, the more stable the quality of the product.
The MacAdams system is used to refine the binning process of LED colors and has now become important in the color-checking process for LEDs. The chromaticity of an LED product (the degree of deviation of its color temperature) is defined in MacAdam ellipses in Standard Deviation of Color Matching (SDCM) - the CIE standard.
As mentioned previously, LEDs are not untouched by color shift issues because there are a variety of factors that can influence chromaticity (color) at the LED Diode, lamp, and luminaire level.
Quality LEDs are less prone to color shifting, however, because LEDs have a much longer lifespan than traditional light sources, color shifting can be more visible with LEDs at the end of their lifespan. The primary cause of premature color shift in LEDs has to do with the manufacturer’s design of the lamp or fixture and the quality of the materials used in the construction of the product.
As an LED lamp or fixture operates over time, materials used in its construction can deteriorate if poorly designed and their properties change, which in turn causes the color temperature of the light produced to change.
Premature Color shift in LEDs is caused by:
Poor Quality material such as the actual LED Diodes
Lamp and Luminaire Design
Use and/or Installed Locations
A "bin" with lower quality diodes will degrade sooner and are prone to color shift earlier. Why use diodes from a wider range of bins? Its cheaper.
Poor quality components, such as drivers and power supplies, can accelerate issues and cause color shift.
LED diode performance is strongly affected by operating temperature (drive current). Excessive temperature fluctuations during operation will shorten the life for most LED components. (see below)
Some manufacturers, in an attempt to get more “Light” out of a diode, will “over-drive” the diode. While this increases lumen output, it operates the diodes at higher temperatures, which increases the likelihood of color shift prematurely occurring.
Some manufacturers, in an attempt to save on material costs will design lamp and luminaires that are not able to properly dissipate the heat generated by the diodes. This causes the diodes to endure higher temperatures for longer periods of time than they were designed and tested to withstand, which increases the likelihood of color shift pre-maturely occurring.
Low quality production or assembly conditions at manufacturing facilities can increase the likelihood of dust and/or dirt intrusion on the interior components of a lamp or luminaire. This additional material can affect the ability of a lamp or luminaire to dissipate heat, which increases the likelihood of color shift pre-maturely occurring.
LED Lamps installed within inappropriate housings or fixtures can result in the degradation of lighting quality.
For example an LED “Corn Cob” Lamp that is being installed in a existing parking lot fixture housing (just replacing the bulb) was not designed to manage the heat that may exist within the housing. Because of the previous lamp type (High Intensity Discharge), the existing housing was not designed to dissipate heat in any way, as it did not affect the performance of the original HID Lamp.
The inability of LED lamps or fixtures to manage high ambient temperatures that were not accounted for in the LED Diode testing process can causes the diodes to endure higher temperatures for longer periods of time than they were designed and tested to withstand, which increases the likelihood of color shift prematurely occurring
With LEDs, end of life is determined by whichever occurs first: catastrophic failure, unacceptable lumen depreciation, or unacceptable color shift. It's well-known that LED lights have lifespans longer other types of traditional lighting. Therefore, poor quality materials, poor engineering and design, and improper use and installation are the primary causes of premature color shift in LED systems.
(More technical information incoming!) Color shift can also be caused by the physical components of the LED, such as phosphor coatings. The majority of LEDs on the market consist of the phosphor coated package type, which means a mixture of phosphors is applied to the LED chip. The degree of color shift depends on how the LED degraded, which in turn depends on the coating method used by the manufacturer.
For example, one coating method demonstrated curling of the phosphor relative to the LED chip, which caused a shift towards blue. Another coating method caused a shift towards yellow when high temperatures caused air gaps to open between the coating and the LED chip (also called “delamination).
Quality design by reputable manufacturers can ensure a long life product with limited color shift. This is what separates a quality manufacturer from a sub-par manufacturer and explains why products for similar applications (for example a high bay fixture from one manufacturer vs another) can vary so much in cost.
Because the value of LEDs is within their high efficiency and long life, it's important that LEDs maintain their CCT over the course of their operational life. Although an LED may achieve high efficiency and good lumen maintenance, if its CCT degrades too early, the practical useful life of the LED can be shortened too.
If you're looking to purchase LEDs, or, fully retrofit your space or facility, Stouch Lighting is here to help every step of the way. We're manufacturer-neutral and can help you choose quality products specific to your space! Click below to schedule your free consultation with one of our lighting specialists: