In our past few posts, we discussed the optimum Color Temperatures for activities like concentrating on math or science in schools and relaxation after exercise.  Why is that?  What is the biological reason for our preference to certain lights for certain activities?  It all relates to our Circadian Rhythm, our body’s natural clock, which regulates the sleep/wake cycle.

What sets our natural clock?  It is not the passage of time, but rather the color temperature of light.  We have specific receptors in our eyes that are particularly responsive to the bluish light we experience in the early morning.  Exposure to even low levels of this light resets the clock, which stops the secretion of the hormone melatonin—the hormone that prepares our body for sleep.  Conversely, this high color temperature light also causes our brains to release hormones like cortisol, which acts to increase alertness, stress response, and control our impulses.  Throughout the day, the light gets brighter, but color temperature decreases steadily to a warmer, less intense light, before sunset.  This warmer light causes the brain to release melatonin to relax us and prepare our body for sleep.

What does that mean for us?  Today we spend more time inside than ever before, exposed to the same constant color temperature light.  With the Sigma Luminous Color Tuning series of LED panels and troffers, you can tune the light color temperature to better mimic the light outside for a more comfortable environment in offices, schools, hospitals, ect.  Set the light to the optimal color temperature to wake up, concentrate, and relax, all from the same light.

The following chart shows the color temperature of light throughout a normal day, 6 am to midnight.  The large spikes right before and right after sunset is due to the reflection of ambient light in the atmosphere.  The color temperature at night is the same as noon light since the light comes from the reflection of the sun’s light on the moon and stars, but the light levels are so low, we don’t perceive it as noon light.

Color Temperature of Natural Light

Natural CCT

If you want to learn more, click on the link below to read our white paper on the Circadian Rhythm and Color Tuning, and stay tuned for our next post, where we will discuss some research into LED Color Tuning.

Additionally, our friends at have a great article on Circadian Rhythm as well. Check it out here.