Light is essential to life

A better life begins with getting the correct light at the correct time.

Light is essential to life

A better life begins with getting the correct light at the correct time.

Humans evolved under natural light

This much is certain: life on earth evolved beneath the sun’s predictable cycle of light and dark. For this reason, our bodies also operate on predictable cycles known as circadian rhythms. Beginning at the molecular level, circadian rhythms dictate when we wake, sleep, eat, even perform at our best, both mentally and physically. But just like mechanical clocks, our circadian clocks can drift. So, our body relies on environmental cues to reset them. The most significant of these cues, known as zeitgebers or “time-givers,” is light.

Historically, the sun provided us with a steady and predictable zeitgeber, delivering us the right light at the right time to continuously keep our circadian clocks in sync. This synced-up state, known as circadian entrainment, relies on photoreceptors in our eyes called intrinsically photosensitive retinal ganglion cells (ipRGCs). Unlike rods and cones—the other two photoreceptors present in the human eye—ipRGCs are not responsible for image formation. Instead, they transform incoming light into signals which are then relayed to multiple regions of the brain. Chief among these regions is the suprachiasmatic nucleus (SCN), our body’s master clock, and the heart of our circadian system. To put it simply, ipRGCs utilize light to keep our circadian clock on time. However, our ipRGCs don’t read all light sources the same.

light+circadian system graphic

Not all light is created equal

Ever since Newton’s work with prisms in the 17th century, it has been known that visible light is composed of different wavelengths on the electromagnetic spectrum. This composition of wavelengths is known as a spectral power distribution (SPD). The human eye perceives these various wavelengths using three types of cone cells: long, medium, and short (which roughly correspond to our perception of red, green, and blue). White light is typically composed of a wide range of colors, or wavelengths, along the visible spectrum. As such, the SPD for full-spectrum white light, such as the light we get from the sun, contains a fairly even balance of wavelengths. The SPD (or “spectrum” for short) for “warm” white light, on the other hand—like one might experience in a dimly lit restaurant—is heavier in red wavelengths. And the “cool” white typically found in a convenience store or pharmacy is heavier in blue.

What’s in a Spectral Power Distribution?

Light is composed of different wavelengths on the electromagnetic spectrum. SPDs are a way to visualize this spectral composition, with wavelengths running along the x-axis and their corresponding intensity plotted along the y-axis.

Spectral Power Distribution
Spectral Power Distribution

The human eye is limited by its reliance on three cone types, leaving it unable to parse out the countless individual wavelengths contained in a given spectrum. Instead, humans bucket these rich compositions of wavelengths more broadly into colors. And much like with mixing paint, different combinations of wavelengths can appear to us as the same shade.

To understand how this is so requires a deeper understanding of color perception. When a cone is stimulated by a photon, it does not know, or care, what the wavelength is; it simply keeps count. Different incoming wavelengths stimulate each cone in different ways, affecting the overall tally. In this fashion, the complexity of an incoming SPD is reduced to just three number totals: one from each of our three types of cones. The brain combines these signals to produce what we perceive as color and intensity. The key takeaway is that our cones measure the sum total of a wide range of wavelengths rather than individual wavelengths of a light source. And because of this, different mixtures of wavelengths can result in the same total count. By this mechanism, it is possible for more than one spectral “recipe,” or combination of wavelengths, to add up to the same apparent color. This is the essence of a concept called spectral agility.

Getting the right light at the right time is critical

Today, humans spend an average of 94% of their lives indoors. Most of the light they receive is artificial, and a growing portion of that is LED. In fact, the Department of Energy expects as much as 80% of light in use will be LED by 2030 (and that estimate doesn’t even factor in displays such as phones, computers, and TVs). With LED technology comes increased efficiency, lifespan, and color flexibility. Unfortunately, most LED spectra have been suboptimal to date, able to support our vision but inadequate to meet our circadian needs.


There are several theories as to how light impacts the circadian system, yet consistent among them is that more light is better during the day and less light is better at night. Unfortunately, artificial light is usually neither bright nor dim enough.

Light has two partially independent properties: photopic lux (or its visual brightness) and melanopic lux (indicating its impact upon circadian system). While artificial light provides enough in the way of photopic lux to support our vision, it generally does not stimulate our circadian system enough during the day. At night, we still want to see, but with today’s light technology this requires too much melanopic lux. This leads our circadian system to experience artificial light as a state of perpetual twilight. Today’s indoor spaces are neither bright enough to be day nor dim enough to be night, resulting in a physiological stupor in which the amplitude of our circadian rhythm is reduced, and its phase is destabilized.

Circadian disruption such as this is terrible. We’re not just talking about lost sleep either. Circadian disruption is linked to a growing host of diseases and disorders, from general malaise and decreased productivity to various cancers and neurogenerative diseases. But if inappropriate light is the root cause, spectrally agile light offers a solution.

We’re shaping light to increase wellbeing

At Korrus, we use spectral agility to separate the visual experience from other beneficial properties of light. This allows us to deliver consistent white light for vision while manipulating its underlying composition to support circadian health. But that’s just the tip of the iceberg. Spectral agility enables white light with other benefits, such as boosted violet for antibacterial applications, boosted deep red for therapeutics, even potential spectra for blood pressure regulation and vitamin delivery.

Full Spectrum

Maximum visual performance and high color rendering

ZEROBLUE™ (Low Melanopic Lux)

Reduced blue signals the end of day without quality loss

Spectral Distribution 5000k

MaxBlue (High Melanopic Lux)

Elicits the circadian response of morning and daytime light

White Disinfection

Boosted 405nm offers a continuous antibacterial benefit

This is not just the stuff of science fiction either. The SPDs above are just four of our patented recipes for high-quality white light, yet each varies widely in the benefits it delivers. Importantly, there is a negligible change to the visual experience across each. No yellow screens, no blue or purple glow. Just the right light at the right time. Increased alertness and focus. Increased relaxation. Even the gradual shifting of our body clock to better adjust to time changes and jet lag. Every single photon of every single day, coordinated and delivered in service of personal wellbeing. All through the power of light.

This is just the beginning of a field called Human Light Interaction (HLI), which seeks to understand human interactions with light and create technologies that better serve the needs of those humans. HLI is dedicated to exploring all potentialities of light, from the examples above to whatever the research yields next. Of course, to take advantage of such a revolutionary re-thinking of light—one that can accommodate new discoveries as they arise—requires systems that are designed to adapt.

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Recommended Reading

Learn more about how light impacts our circadian system, mood and physical health.
The Circadian Code
Why We Sleep