Thanks to advancements in color tuning and lighting control technology, it is now possible to imitate the complex nature of daylight indoors.
Lighting control systems can mirror the variations in intensity and color that are intrinsic in the sun’s daily cycle and deliver these different types of light at the right time of the day. Lighting controls pave the way for interior spaces that support the internal clock of the human body, offering a healthier and less disruptive alternative to the traditional built environment.
Daylight is a dynamic light source. Over the course of the day, it transitions through different intensities and colors. Beginning in the morning, the natural light level builds in intensity toward its noontime high, and the color temperature moves quickly from a warm, orange-yellow at dawn to a cooler, crisper blue-white. In the afternoon, the intensity of the light from the sun wanes until sunset, and the color temperature warms from a cool white into the richer yellow glow of dusk.
The human body is incredibly attuned to and dependent on the sun’s daily routine. Many of the internal systems that regulate our physical, mental and behavioral well-being are evolutionarily programmed by the natural pattern of daylight and darkness. Unfortunately, people today have dramatically reduced their exposure to daylight, spending increasingly more time inside. It is estimated that Americans spend approximately 90 percent of their time indoors. In many cases, this means we are regularly underneath artificial lighting that provides one color of light, at a single intensity, from morning to night.
Eliminating a person’s exposure to daylight and the temporal cues it provides can have disastrous consequences on the circadian rhythms of the body. Circadian rhythms are biological cycles that repeat approximately every 24 hours and are regulated by environmental signals. They play a large part in governing hormone release, body temperature and sleep/wake cycles. Disruption of these natural rhythms has been associated with an increased risk for a cardiovascular event, obesity, diabetes, neurological problems such as depression, and even some forms of cancer.
Now lighting systems can be designed to support the entrainment of the circadian system by providing varying degrees of circadian stimulus (CS), a metric developed by the Lighting Research Center at Rensselaer Polytechnic Institute, throughout the day. In fact, Alzheimer's light therapy is an exciting potential treatment for this progressive and most common form of dementia. Light therapy for dementia is just one example of how circadian rhythm lighting can potentially improve health.
“We developed a metric, circadian stimulus (or CS) to assess the impact of light spectrum and amount on one output of the circadian system, namely, melatonin suppression,” said Mariana G. Figueiro, Ph.D, professor at the Lighting Research Center. “We have shown that exposing various populations (Alzheimer’s disease patients, office workers, submariners, adolescents) to a CS of 0.3 or greater has been associated with better sleep and mood. A CS of 0.3 is equivalent to suppressing the hormone melatonin by 30 percent after one hour of exposure to that light in the middle of the night.”
The CS value of a specific lighting environment is determined by multiple factors: the intensity of the light, the color of the light, the timing and the spectral power distribution of the fixtures. Circadian systems are more sensitive to cooler, blue-white light. Lighting with a color temperature of 6500K, generally regarded as the color of daylight, is most effective at stimulating the circadian system; however, it is not necessary to use light with this color temperature to deliver adequate circadian stimulus into an interior space. Lighting with a warmer color temperature such as 3000K does not contain as much of the circadian rhythm-friendly blue light, so the intensity of the 3000K light must be increased to ramp up a person’s exposure to the blue wavelength light that it does contain.
This means that designers can create circadian-supportive interior environments with tunable or standard luminaires. Tunable luminaires, capable of offering changes in both color and light intensity, can be programmed to modulate the light intensity and color temperature of the lighting environment over the course of the day. Adequate CS values can also be achieved without changing the color temperature of the lights. This sufficiently increases and decreases the light output of the system at certain times.
Another distinction of circadian lighting is the consideration of the vertical illuminance available at eye level, and the balance of that eye level illuminance with the light targeted on the work plane. Traditional lighting design practices focused upon the amount of light illuminating the work plane, but the circadian system is stimulated by the light it receives through the eye. For a lighting environment to stimulate the circadian system, the carefully calibrated lighting dose of light intensity, color and timing must be delivered to the corneas of the occupants in the space.
“The right dose of lighting at the right time can create a powerful impact on the sleep and mood of the people in a space,” Figueiro said. “Our bodies are programmed to receive a robust light-dark pattern; we just have to bring those light (or daylight) and dark cues indoors.”
For more information on calculating the CS value of lighting design, refer to the Circadian Stimulus Calculator created by the Lighting Research Center.