Light is life. When you think of life on this planet- plants, animals, humans- they are all impacted by light and the cycle of the sun. Light is the oldest input, and a significant nutrient for biological functions throughout the web of life.
Light is the most powerful time cue for our 24-hour circadian clock. It tells us when to wake up, when to get sleepy, when to product certain hormones and when to lower or raise our temperatures. It regulates our sleep, which is imperative for health and cognitive function, as sleep aids in healing, restoring and rejuvenating the physical body and our mental capacity.
The most impactful wavelength to humans’ biology in the visible spectrum is blue. Within the visible spectrum, 480 nanometers (visibly blue) is most impactful to humans and circadian rhythm regulation, and its presence or absence triggers a multitude of biological responses.
Light has two main effects on alertness. Firstly, light as a stimulant increases alertness and improves performance, depending on its wavelength and intensity. Blue-enriched light (specifically blue light around 480 nanometers, the peak of melanopsin sensitivity) and high intensity light directly alerts the brain and can be used at times when alertness and productivity need to be heightened; for example, during daytime or at work.
Light has a second effect on alertness via its impact on our 24-hour circadian clock. Alertness and performance rhythms are strongly regulated by the clock, so when the clock is shifted (e.g. staying up later or waking earlier), the timing of peak alertness and performance shifts accordingly. Maintaining exposure to a stable light-dark cycle (bright blue-enriched days and dark nights, and a habitual sleeping pattern) is needed to maintain good circadian entrainment, including alertness and performance patterns.
Wavelength and intensity are characteristics of light that can be combined to improve circadian impact. LED technology allows lighting manufacturers to manipulate those characteristics and create a variety of lighting outputs. Because light is a stimulant, and there are certain wavelengths that are extra energizing, lighting products can be designed for this purpose. (See our GoodDay® Products)
Before sleep, however, these alerting effects need to be minimized, otherwise it will be harder to fall asleep and the quality and depth can be compromised. Exposure to blue-depleted and dimmer light is therefore recommended for as long as possible before sleep. (See our GoodNight and SleepyBaby products)
Sleep is vital for good health. In the short-term, poor sleep leads to sleepiness, fatigue and poor performance, which can impact safety and performance at work or while driving. The American Academy of Sleep Medicine recommends a minimum of 7 hours per night in adults, although often people need more to maintain optimal performance. Sleep should be prioritized each and every night, as it’s very hard to ‘catch-up’ on sleep, even on weekends.
Longer-term, sleep deficiency has been linked to an increased risk of high blood pressure, heart disease, stroke, diabetes and some types of cancer. There is also a strong relationship between poor sleep and mental health, including the risk of depression. These risks are exacerbated in individuals who routinely sleep poorly, for example in shift workers; and the World Health Organization has designated shiftwork that causes circadian desynchrony a ‘probable carcinogen’. Sleep should be considered one of three pillars of good health, along with diet and exercise, and should be prioritized as part of a healthy lifestyle.
While multiple factors play a role in the biological impacts of a light source, the spectrum (wavelength) and intensity (brightness level) are the most important components. Increasing the blue content, especially around 480nm, of white light as well as increasing intensity will improve the alerting impacts of light. Daylight, for instance, induces a high level of alertness response given the combination of both its blue content and high intensity. Achieving alertness responses indoors oftentimes requires altering the specific type of light and the indoor light levels to increase blue content or increase intensity. This has potential to alter the health benefits of the light you are exposed to in indoor environments.
Our current standard of measuring light is focused on illuminance (lux), which intends to estimate the visual (photopic) effects of light. However, non-visual (melanopic) effects can in fact be measured. As light is a stimulant, and certain properties provide more stimulating effects than others, it is those properties that circadian lighting technology seeks to manipulate for desired effects. These effects are measured in what we call an m/p ratio (melanopic/photopic ratio), and lighting manufacturers present this information in a decimal form, for instance, 0.3 or 0.9. The lower the decimal, the better that light is for evening hours before sleep. The higher the decimal, the greater that light’s effect is on your biological system, meaning you’ll want a higher value for alerting effects during the day.
Corelated Color Temperature
This is measured in Kelvin and tells how warm or cool the light is. A higher temperature means a cooler, more bluish light. A lower temperature will be a warmer light, and will look more yellow. Color-tuning products use CCT to determine if a light is good for day or night, but it is not an accurate means to determine biological impact.
The Brightness of Light
The intensity of light for LEDs is sometimes measured through a comparison unit: equivalent watts. In traditional lighting, the wattage was directly related to light output, so LED lighting uses ‘equivalent watts’ for familiarity, but wattage is no longer reliable for determining how bright a light can be, because LEDs are much more energy efficient. The intensity of light is relevant to the m/p ratio, in that a brighter light will have a higher biological impact, offering more alerting effects.
Color Rending Index
This is how well a light source renders colors. A high CRI is helpful to see colors and contrast, leading to higher visual acuity. Depending on the types of wavelengths that make up a light, colors will look different, and certain ones will ‘pop’ under different light sources. For crisp, clean light, and true color visibility, a high CRI of 90 or above should be sought.
This is a measurement that demonstrates a lamp’s biological impact. The lower the decimal (i.e. .34 or less) the better the lamp is for light before sleep. The higher the decimal (over .90) the better that lamp is for alertness and daytime use. While color tuning products use CCT, for true biological lighting, look for the m/p ratio.