Light spectrum or color temperature? These terms are often used interchangeably to describe the visual appearance of light, but when it comes to your health, light spectrum matters.
Research shows that light spectrum plays an important role in regulating our body’s biological clock—our “circadian rhythm.” Our bodies evolved exposed to changes in light spectrum throughout the day. As a result, light spectrum and intensity trigger hormonal cycles in our bodies–and have a profound impact upon our health and well-being.
Today, people increasingly spend their days indoors with limited exposure to daylight. Most people don’t get enough light during the day, but get too much light at night. The impact on health risks, such as cancer and obesity, are being widely studied.
Fortunately, much has been learned over the last two decades about the physiological mechanisms that control our body’s response to light. We now understand the composition and intensity of light needed to impact our biological clock. In additional, tunable LED technology now provides the opportunity to customize light spectra to better support our body’s natural circadian rhythms.
In order to make circadian light spectra easier to understand, consumer information generally describes light with ‘high blue content’ as most beneficial during the day. Conversely, light with ‘low blue content’ is most beneficial in the evening as it allows the body’s natural production of the sleep hormone, melatonin.
Correlated color temperature (CCT) is another term that is often used interchangeably with light spectrum. Lighting with high CCT, for instance, is referred to as “cool white.” It has a bluish appearance with ‘high blue content’. Lighting with low CCT, in contrast, is referred to as “warm white.” Low CCT light has a more amber appearance.
The term “blue content,” however, is somewhat misleading. The term originated because our eyes’ photoreceptors, which signal the circadian system, are the most sensitive to light at a frequency that looks blue. Interestingly, most of the light that we encounter on a day-to-day basis is not comprised of just one color frequency, but many. As a result, it’s hard to identify all of the color frequencies within a particular light without using special tools. Daylight, for example, contains all the colors of the visible spectrum.
Generally speaking, light sources with a low CCT (within the 2000K to 3000K range) have less impact on circadian photoreceptors than light sources with a high CCT (in the 5000K – 7000K range). Because light spectrum composition varies, however, not all light sources with the same CCT will have the same circadian impact.
For example, I tested a couple of commercially available light sources and found that despite matched light levels, a light source with a CCT of 6230K can actually have less impact on circadian photoreceptors than a light source of 4980K. So when it comes to evaluating a light’s circadian effect, light spectrum is more important than CCT or color appearance.
These days, color tunable lamps and light fixtures, which allow the same lamp to produce different CCT levels, are increasingly available. But choose carefully, because when it comes to your health, all light is not created equal. The GoodDay® lights by Lighting Science are engineered to maximize circadian impact at a CCT of about 5000K. Paired with their excellent color rendering performance, the GoodDay® light is superior to many ‘high blue content’ CCT solutions. Best of all, 5000K delivers the same color temperature as direct sunlight in the morning, which makes it a great way to start your day!