Table of Contents Hide
- 1 Designing Lighting in Accordance with the Circadian Rhythm
- 2 What Is Tunable White Lighting
- 3 The Science behind White Light
- 4 Brings the Dynamics of Natural Daylight Indoors
- 5 How Tunable White Lighting Works
- 6 Tunable White Applications
Designing Lighting in Accordance with the Circadian RhythmTunable white lighting is a dynamic white lighting technology developed to support the concept of human centric lighting (HCL). Until recently the lighting industry had been placing its emphasis on products and solutions that provide visual sensation in humans and facilitate perception of the visual environment. The discovery of a third photoreceptor in 2001 has transformed our understanding of how light interacts with the human organism. Light not only provides visual sensation through rod and cone photoreceptors, but also influences biological processes in the human body by stimulating the non-visual photoreceptor called intrinsically photosensitive retinal ganglion cell (ipRGC). Human centric lighting, which is designed to evoke non-visual human physiological responses through biologically effective lighting, was initiated on this discovery and is driving the technology trend in the lighting industry.
What Is Tunable White LightingTunable white lighting refers to dynamic control of color temperature and light intensity of a lighting system, with the intention of aligning lighting with circadian rhythms or key activities that require occupants to be more physiologically and psychologically engaged. This technology harvests superior controllability and color mixing performance of LEDs to create a tunable mixture of white light. The dynamic feature of tunable white solutions allows any color temperature within the mixing range to be called up. Along with independent, full range control of light output, tunable white lighting systems can simulate the drama and variety of natural light for a positive effect on human health, well-being and performance.
The Science behind White LightNot all white light is created equal. Similar to the way natural daylights comes in different tones, white light has its own variations in appearance. Correlated color temperature (CCT) is a color metric that quantifies the appearance of a white light source. White light with color temperatures at 3000 K or less is called "warm white" because it has a relatively reddish tone, whereas white light at 4000 K or greater has a relatively bluish tone, like moonlight on snow, and is therefore considered "cool white". And white light with CCTs between 3000 - 4000 K is called "neutral white" as it does not excessively emphasize either red or blue in its appearance. For a long time, people has related CCT to merely the visual impression of white light in different tones. But the light spectrum behind every CCT value is inherently tied to biological processes in the human body.
The human biological clock has evolved to cycle with the 24-hour rhythm of the solar day through circadian phototransduction. Circadian phototransduction is a biochemical process in which three photoreceptors (rods, cones and ipRGCs) in the retina convert received light into electrical signals for the circadian system. Among three photoreceptors, ipRGCs play a dominant role in this process. They transmit signals emanating from the retina to the suprachiasmatic nucleus (SCN) in the hypothalamus region of the brain where the circadian system is located. The SCN is the body's master biological clock which orchestrates the circadian system and synchronizes the sleep-wake rhythm to the natural light-dark cycle using signals provided by the photoreceptors. The master clock co-ordinates and synchronizes peripheral clocks located in other tissues outside the SCN. Thus the circadian rhythm established by the SCN influences various aspects of human biology, endocrinology, physiology, metabolism, and behavior.
From sunrise to sunset, the dynamic changes in the color temperature and illuminance of daylight have been genetically registered in our biology as a system of internal clocks that include the master and peripheral clocks. Melanopsin, the photopigment that drives the ipRGCs' photosensitivity, reacts specifically to light at the blue end of the spectrum. It is most sensitive to bright daylight and exhibits peak photosensitivity during the midday hours when the light spectrum contains the highest percentage of blue. Stimulated by the blue wavelengths in the daylight spectrum, the ipRGCs work through the SCN to encourage the production and release of cortisol, the stress hormone that stimulates the metabolic process and programs the body into day mode. The ipRGC photoreceptors also promote secretion of serotonin and dopamine needed for enhancing pleasure, alertness, coordination, and mood.
Exposure to bright, blue-rich light has been shown to suppress the production of melatonin that is unwanted during the day because it promotes sleepiness. Nevertheless, melatonin is a critically important hormone that decides the quality of restorative sleep during the night. Unlike cortisol, which is promoted during light exposure, melatonin is suppressed by bright light, in particular the blue-rich cool white light. As the sun sinks in the west, the daylight ambiance is stronger in the red part of the spectrum. The SCN will respond to the changes in light spectrum and reduced light intensities by signaling pineal gland to release melatonin at night and under conditions of darkness. However, a sudden introduction of bright, high color temperature light in the middle of the night will interrupt melatonin production, which can lead to fatigue during the day.
Brings the Dynamics of Natural Daylight IndoorsAs presented above, light does not just provide visibility that enables us to see things and perform activities, it regulates the biological processes in our body. High intensity, cool white light with a high percentage of blue in its spectrum has an energizing effect on the human body, while low intensity, warm white light such as that of the setting sun unleashes the release of melatonin and makes people sleepy and relaxed. We spend most of our time indoors living, working, and playing under spectrally uniform and consistent artificial light. This can disrupt the natural circadian rhythms that we have been conditioned in the course of human evolution. Circadian disruption will negatively affects the entire body, including sleep, alertness, mood, digestion, immune system and physical performance. Subsequent health effects include increased cancer risks (especially for breast and colorectal cancer), depression and mood disorders, cardiovascular diseases, impaired functioning of the immune system, reproductive problems, and diabetes.
Tunable white technology allows artificial emulation of the natural cycle of daylight that defines our 24-hour internal clock. Dynamic white systems with tunable wavelengths and lumen output can be programmed to change spectral power distribution (SPD) and light intensity over the course of the day to deliver biologically effective light at the right spectrum and radiation time. Aside from synchronizing our endogenous circadian rhythm to the natural sequence of day and night, tunable white lighting can evoke particular human biological responses to achieve enhanced effects. For example, different types of daylight activities can be performed under light exposure with task-specific spectrums and intensities for maximal productivity or engagement. Tunable white lighting can also be used to create emotionally triggering environments and set appealing atmospheres that support positive psychological stimulation. A soft, warm ambiance, for example, often encourages relaxation, imparts a feeling of intimacy, and contributes to hospitality and comfort of an interior space.
How Tunable White Lighting WorksTunable white lighting systems use wavelength or color mixing of a number of controllable channels to create the diversity of color temperatures. The mainstream method is 2-channel Warm-Cool mixing which adjusts color temperature by changing the relative intensity of cool white LEDs (short wavelength radiation) and warm white LEDs (longer wavelength radiation). The challenge for this method is to ensure CCT transition follows black body curve. The tunable white spectrum usually covers the entire CCT range from 2700 to 6500 K or 1800 to 6500 K. Simple intensity mixing of warm and cool LEDs over a wide CCT range will create a straight line that falls off the black body curve at the center. This will make the tint pink, instead of neutral tint when the color point is on the black body curve. Separate control inputs for intensity and color temperature are required to ensure that the color temperature remains constant when intensity is adjusted and vice versa. The control inputs for these fixtures can be 0-10V, CCR, PWM, DMX, or DALI control.
Additive color mixing refers to the mixing of at least three primary colors (red, green, blue) to create secondary colors. Additional color LEDs can be included to improve color quality. The benefits of primary color systems (RGB, RGBA, RGBW, or RGBAW) include that any color temperature along the black body curve can be produced and the mixture of light has excellent color rendering over the entire CCT range. RGB color mixing requires a sophisticated controller that provides signal interpretation and runs color mixing algorithms for regulating the current to individual LEDs.