Color shift, also termed color maintenance and chromaticity shift, has posed a challenge in the lighting sector for a long time. This phenomenon might go unnoticed by users if the alteration occurs gradually within regular light levels and space color. Yet, for certain products, this color change becomes conspicuous and problematic. Traditional technologies like metal halide and fluorescent lights suffered from this issue significantly after minimal operating hours.
In contrast, high-quality LEDs are less susceptible to this issue. However, there’s now a growing awareness within the industry about the necessity to tackle color stability.
It’s vital to differentiate between color stability and color consistency. Color stability pertains to a product’s capacity to sustain unchanging color (chromaticity) as time progresses, whereas color consistency means the variation in chromaticity among supposedly identical lights or fixtures within a manufacturer’s batch. When addressing color shift, the main focus lies in color stability.
What Is Color Stability?
Color stability represents a crucial yet often disregarded attribute of lighting products, denoting their capacity to uphold consistent color characteristics over time. Even if lights are produced with uniform correlated color temperatures (CCTs), their color properties can alter throughout their lifespan. The color of the emitted light is tied to the wavelength of the radiated energy. This connection between color and temperature is why we describe a light source’s color as its temperature.
For instance, incandescent lights emit a warm, white color, skewed toward the yellow-orange segment of the light spectrum. In contrast, metal halide lights lie higher on the color spectrum, producing a cooler white shade that tilts toward the blue part of the spectrum. The degree of color stability varies depending on the specific product and the manufacturer.
What Is Color Shift?
Have you ever observed multiple pole lights in a parking lot, each emitting a slightly different color? This phenomenon is attributed to color shift, which happens when a light source undergoes notable changes in its spectral output. Consequently, this leads to alterations in the Correlated Color Temperature (CCT) and color rendering properties (CRI) of the light source as it operates over time. In essence, color shift signifies a gradual change in the produced light’s color.
Typically, this shift leans towards the blue segment of the spectrum, resulting in a loss of colors outside of the blue emissions. Nonetheless, this deviation can also impact green and red emissions. Diverse chips will exhibit varying color changes based on the attributes of the phosphorus employed in the LED chip. A helpful analogy for understanding color shift is likening it to lumen depreciation in specific parts of the LED’s color spectrum.
What Causes Color Shift in LEDs?
While superior LEDs are less susceptible to color shifting, the extended lifespan of LEDs can amplify the visibility of color shifts as they near the end of their operational life.
The key reason behind the untimely color shift in LEDs relates to how the manufacturer designs the lamp or fixture and the quality of materials employed in its construction. As an LED light operates over time, subpar design and materials can lead to their deterioration. This, in turn, results in changes to the color temperature of the generated light.
Poor Quality Material
Incorporating components of inferior quality, like drivers and power supplies, can expedite problems and contribute to color shift. The operating temperature, determined by the drive current, greatly impacts the performance of LED diodes. Excessive temperature variations during usage will curtail the lifespan of the majority of LED components.
Certain manufacturers may opt to “over-drive” diodes to maximize light output. However, this practice raises the operating temperature of the diodes, heightening the risk of early color shift, despite the increased lumen output.
Manufacturing facilities characterized by subpar production or assembly conditions can increase the chance of dust or dirt infiltrating the internal components of lights or luminaires. This added material can impede the heat dissipation capability of these fixtures, thereby amplifying the likelihood of premature color shifting.
Placing LED lights in unsuitable housings or fixtures can lead to a decline in lighting quality. For instance, installing an LED “Corn Cob” light into an existing parking lot fixture housing without design consideration for heat management can heighten the probability of premature color shifting. The housing might not have been designed to dissipate heat due to its previous use with HID lamps.
Other Potential Causes
The source of color shift can also originate from physical elements within the LED structure, like phosphor coatings. The majority of LEDs available employ a phosphor-coated package configuration, wherein a blend of phosphors is applied to the LED chip. The extent of color shift is contingent on the degradation pattern of the LED, influenced by the coating technique employed by the manufacturer.
For instance, one coating approach exhibited phosphor curling relative to the LED chip, inducing a shift toward the blue spectrum. Alternatively, another coating method prompted a shift toward the yellow spectrum. This was due to high temperatures causing the formation of air gaps between the coating and the LED chip, a phenomenon termed “delamination.”
How to Prevent Color Shift in LEDs?
Opting for the right chip tailored to the specific application can lessen the occurrence of color shift. Therefore, when making this critical decision for your lighting system, it’s imperative to evaluate its lifespan by examining the LM80 data, offering insights into how a chip will age.
Moreover, ensuring that the PCB board manufacturing adheres to stringent quality assurance procedures and meticulously follows the chip manufacturer’s mounting instructions is essential.
In fact, the most effective preventive measure is to prioritize meticulous heat management within the luminaire. A well-cooled, high-quality LED, even under elevated current conditions, is unlikely to experience color shift. This emphasis on heat management holds paramount importance in our new product development approach, in contrast to certain unmentioned companies that may neglect this aspect.
How Does Color Shift Differ from Lumen Depreciation?
Lumen depreciation refers to the overall reduction in emitted light across the entire spectrum. As previously mentioned, color shift can be seen as a form of lumen depreciation that occurs disproportionately in specific segments of the spectrum. To illustrate, a shift towards the blue spectrum signifies a greater decline in light intensity from the other parts of the spectrum, rather than an actual augmentation of the blue region.
Is Color Shift Exclusive to Regions with High Temperatures?
No, but color shift is more likely to manifest faster in regions with high temperatures. A light source that exhibits color shift in a cooler climate like Finland will almost certainly experience the same issue in a hotter environment like Qatar. Therefore, high-temperature climates can be considered a definitive test of both quality and heat management.
Opting for long-lasting products with minimal color shift by well-regarded manufacturers is crucial. This distinction separates reputable manufacturers from lower-quality counterparts and clarifies why products designed for similar applications, such as a high bay fixture from one manufacturer versus another, can have substantial cost variations.
Given that LEDs’ value lies in their efficiency and extended lifespan, it’s crucial for LEDs to uphold their Correlated Color Temperature (CCT) throughout their operational duration. Even if an LED exhibits high efficiency and satisfactory lumen retention, premature degradation of its CCT can curtail its practical lifespan.
If you’re in the market for LEDs or considering a comprehensive retrofit of your space or facility, MokoLight is available to assist you at every phase. We offer unbiased advice and can aid you in selecting quality products tailored to your specific environment. Feel free to talk with one of our lighting specialists.