Light affects our sleeping patterns, so much so that distinct aspects of it, like brightness or color, each have a big impact on how we sleep. Subsequently, we tend to see the widespread use of artificial light as problematic: blazing LED lamps keep our surroundings bright well into the evening; harsh screen backlights push our bedtimes back by hours.
But artificial light does have one thing going for it: because it’s artificial, we can tailor it to better suit our needs. Light fixtures, after all, vary in size, brightness, or even color. It goes without saying that brighter lights are worse for inducing sleepiness, but intensity isn’t the only quality worth considering when picking out your lights. Tint, for example, can be just as important—and when it comes to artificial lights, that means taking a closer look at the concept we call “color temperature.”
What is Color Temperature?
A working lightbulb will feel warm to the touch, but let’s be clear: that’s not where the term “color temperature” comes from. In fact, the idea of color temperature has very little to do with how warm or cold a light fixture actually runs when used.
Color temperature refers to the quality of light that a bulb emits. Specifically, it indicates the tint of that emitted light. Two bulbs may both emit “white” light, for example, but if they have different color temperatures, the feel of their emissions will not be the same. Bulbs with a color temperature in the lower range appear “warmer” to the eye, while those in the upper ranges give off light that looks “cooler.”
How Do We Measure Color Temperature?
What range do we mean when we talk about color temperature? Imagine, for a minute, a slab of a solid black material, like steel or iron. When that material is heated, it begins to glow. The color of that glow shifts as you ratchet up the heat. The block starts with a reddish glow; as you continue applying heat, that glow would move on to orange, and later, blue. (This might seem a bit counter-intuitive, but the color of your heated block of material will look “cooler” the hotter it is!)
Each color corresponds to a certain range of temperatures, which are measured using the Kelvin scale. This phenomenon is the basis for the measurement system called “correlated color temperature,” or color temperature for short: you can describe the tint of light using the temperature range that would produce the same color glow.
The Color Temperature Range
When it comes to artificial lighting, bulbs and other sources typically have color temperatures somewhere in the 2000K – 8000K (Kelvin) range. Here’s a brief look at what common color temperature ratings mean, and what kind of effects you can expect from each:
< 2000K: Candlelight
In this range, light sources emit a warm, dim glow, like what you might get from a flame. The light itself is likely to be more diffuse, resulting in ambient illumination rather than the more “focused” beams of brighter sources.
2000-300K: Incandescent Light
At this range, you can expect light to have yellowish tints and a soft, cozy feel overall. Lights in this range retain the “warm” feel of lower color temperatures but provide more focused and clear illumination.
3000-3500K: Neutral Light
At this point, sources emit light that skews closer to a “pure white,” with only the slightest yellow tints. Illumination in this range appears brighter to the eye, inducing alertness without being too harsh.
3600-4500K: Cool White Light
Sources in this range emit a starker white than neutral lights. They deliver more clarity, and the lack of warmer tints in the lighting makes it easier for the human eye to focus on smaller details in the environment.
4600K-6500K: Bright White Light
Sunlight typically comes in at around 5800K on the color temperature scale, so lights in this range are closer to the “blue-tinted” white light of daytime. At this point, lights also appear “brighter” to the eye, because they lack the softening effect of warmer tints; they’re also more likely to appear harsher and to induce fatigue in the eyes from prolonged exposure. That said, bright white light is also crisper than sources from preceding ranges, creating fewer shadows and making for a better environment for tasks that require attention to detail and heightened alertness.
6500K<: Clear Sunlight
At this point, light sources possess a more pronounced bluish tint, and they’re bright enough to occasionally mimic the glare of daylight on a clear, sunny day.
Using Color Temperature for Better Sleep
How can a deeper understanding of color temperature help you sleep better?
For starters, it gives you another good metric for pickings lights to put in your bedroom. Most artificial lights today use LEDs, which skew closer to the blue end of the color temperature spectrum. As you might have gleaned from our article on melanopsin, bluish light can have a negative impact on your sleeping patterns. In fact, studies have shown that exposure to lights with higher color temperatures (a bluer tint) can reduce the amount of time you spend in stage 4 or REM sleep.
For your bedroom, it’s better to seek out lights that give off a warmer tint, i.e., that have a lower color temperature rating. This can be as simple as using incandescent bulbs, or you could ask for LEDs that have been specifically designed to emit softer, warmer lighting. We’ve also got a few more tips about crafting a bedroom that’s designed—and lit—for better sleep, so be sure to check those out!
Your choices don’t have to stop at the bedroom, though. Color temperature can help you be more strategic in light fixture placement throughout your home, or even your workplace, if possible. After all, light’s regulatory influence on our circadian rhythms doesn’t begin and end at bedtime; our exposure throughout the day adds up.
If you spend a lot of time indoors or exposed to artificial light, then, you can use color temperature to design lighting environments that mimic the natural progression of daylight. If you spend most of the day in your home office, for example, you could install lights in the 3600-6500K range to simulate the effects of spending those same hours out in the sun. You can then use light sources with lower color temperatures for those areas where you tend to stay in the late afternoon or early evenings, like your living room or dining room.
Even if you’re not inclined to overhaul your own lighting installations, color temperature can also serve as a good guide for managing your light exposure throughout the day. Modulating the influence of light on your sleeping patterns can be as simple as moving to spaces with more appropriate color temperatures as needed. If you’re feeling sluggish and need a subtle boost, for example, you could relocate to a section of your workspace with brighter, more bluish lighting. Conversely, if you’re winding down for the day, you could turn off brighter light sources in your vicinity or switch over to a softer, warmer light.