As the link between light and health grows, so has the understanding that CCT and CRI are not adequate to characterize circadian lighting, neither during daytime nor at night.

 

By David Shiller

A recent report from MarketsandMarkets projects that the global “Humancentric Lighting Market” will grow from $810 million in 2019 to $3.7 billion by 2024.  This is more than a 4-fold increase over the next 5 years, and a compound annual growth rate (CAGR) of 35.2 percent. There was a time when circadian lighting literature discussed using a cool CCT during the day and warm CCT at night. That’s no longer the case. With a growing understanding of the “relative circadian spectral sensitivity curve,” it’s now understood that it’s possible to have cool CCTs with poor circadian stimulus and warm CCTs with too much circadian stimulus. Specific areas of the blue spectrum need to be “enriched” during the day, and “depleted” at night. This is the rationale behind a growing trend of “no-blue” nighttime lighting products.

Blue Light At Night.

Circadian lighting is going mainstream. The healthcare and senior living industries are rapidly adopting circadian lighting. In addition, a recent ANSI standard from the American Petroleum Institute (API ANSI RP-755) defines fatigue risk management systems for personnel in the refining and petrochemical industries. API RP-755 has added language that requires adequate light and, “…light sources at night should be selected to minimize circadian system disruption.”

According to Dr. Martin Moore-Ede, a former Harvard Medical School professor and advisor to the API Panel, “The only practical way to meet the new ANSI requirement of well-lit workplaces that minimize circadian disruption at night is to use white light fixtures that are spectrally engineered to emit less than 2-percent blue content at night. Dimming the lights at night or using low color temperature (CCT) yellow lighting does not meet the requirement for well-lit workplaces.
Conventional fluorescent and LED lights are far too rich in blue content and cause severe circadian disruption at night.”

Dr. Moore-Ede is also CEO & Founder of Circadian ZircLight, a leading commercial lighting manufacturer in this market headquartered in Stoneham, Massachusetts. Dr. Moore-Ede shares, “400-490 nm are our most sensitive wavelengths for circadian entrainment and disruption. We need <2 micro-W/cm2 at night and >20 micro-W/cm2 during the day. A typical office provides 300-500 lux at tabletop. The above dosages of blue correspond to <2% blue at night and >20% blue during the day.”

He adds, “2700K and similar CCTs still provide too much blue at night. Our products provide <2% blue at night.  They use 415-420nm violet pumps with phosphor conversion for real white light with very little circadian disruption. Furthermore, UL verified our products to be less than 2-percent blue at night.  The only light that penetrates below 150-200 meters in the ocean is 475nm blue light. This is why our circadian system is evolutionarily at peak sensitivity around 475nm.”

When asked if he thinks the no-blue trend oversimplifies circadian lighting, since intensity, duration, time of day, user age, and spectrum all impact circadian entrainment and disruption, Dr. Moore-Ede says he is not concerned. “Blue light at night leads to glucose intolerance and insulin resistance, which could increase risk of diabetes. People get hungrier under blue light at night and gain weight,” he notes. Dr. Moore-Ede sees blue-depleted light at night and blue-enriched light during the day as the future and predicts growing interest globally in products that meet that criteria.

Dr. Moore-Ede reveals, “Our options for healthy light at night are an extremely yellow light, white light dimmed way down, or blue-depleted white light. Yellow light isn’t liked and has poor CRI, [while] dimmed down white light still has negative circadian impacts. Blue-depleted white light is the best option at night. [Between] 415-420nm enriched light provides more alertness without disrupting the circadian system.” As further evidence of the growing trend, Circadian ZircLight light engines and controllers will also be used in some Acuity Brands products.

Another leading company in this market is healthē by Lighting Science. Rather than “no-blue,” healthē focuses on enriching and depleting the blue wavelengths that create the greatest circadian stimulus/disruption. Jay Goodman, VP/Strategy states, “We don’t claim ‘no blue,’ rather ‘cyan-depleted’ (for night) and ‘cyan-enriched’ (for daytime). 480nm is peak sensitivity for the circadian sensitivity curve. Other blues are present in our cyan-depleted products. In the future, we will extend to wavelengths beyond the visible spectrum” (a reference to ultraviolet and infrared wavelengths).

When asked if he sees any risk that the no-blue trend oversimplifies circadian lighting, Goodman comments, “I agree completely that intensity, duration, time of day, user age, and spectrum matter, but we should get the spectrum right first, as it is the most technically challenging to solve, and then the other variables are less complex to address. Regarding intensity, a cloudy day can be 1,000 footcandles, while most offices are around 30 to 50 footcandles.” That’s ~0.5 percent or less of the intensity of a cloudy day. Goodman adds, “Any light at night is disruptive to sleep. Light – including the circadian-sensitive curve – is more disruptive, and cyan-containing light is the most disruptive.”

Another example of no-blue products is Soraa’s ZeroBlue line of lamps. Similar to Circadian ZircLight, they’re another product line using phosphor-converted, violet-pumped LEDs to deplete blue from the spectrum. Additional information on all of these companies’ products can be found on their respective websites.