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Zumtobel has a suite of products available aimed at at replicating the Circadian cycle. At the left is a chart reflecting the use of natural light as a model for its “Active Light” series.

Doping Light for Circadian Effect A hot topic that elicits a great deal of noise, lighting affecting Circadian rhythms is often founded on but a few morsels of solid news. For those seeking a path through the noise, a good start can be found in the NIH manuscript ‘Effect of Light on Human Circadian Physiology’ (Duffy, Czeisler) published in June, 2009 (available on line for free). This provides an excellent summation of the response of subjects in laboratory conditions, under various illuminance conditions and exposure times, and includes several variables, such as individual sensitivity, polymorphism, and other variables that are not well understood. The application of the knowledge covered in the included studies has been applied to developments in treatment of sleep disorders, as well as regimens for night shift work and air travel. This is a newsworthy read. In October, 2016, the Lighting Research Center published a guide titled “Designing with Circadian Stimulus” (Figuero, Gonzales and Pedler), outlining several key considerations in achieving desired results. The guide explains the relationship between CCT, SPD, illuminance levels, the Circadian Stimulus (CS) metric, vertical vs. horizontal illuminance effects, and lighting system features that enhance and detract from CS performance. This guide shows that CCT is


Through it’s tunableWhite offerings, Zumtobel makes the contention that lighting can differentiate spaces based on time and task that can be personalized. While it recognizes SSL won’t be able to completely replicate nature, this seems a bit of “noise,” as more research is necessary, particularly as to whether high CCT delivers more light in circadian response.

less important than identifying SPD of sources coupled with illuminance levels. This guide is accompanied by a fantastic spreadsheet (avail-

light stimulus and the resulting non-visual

of daylight peaks. Humans have lived under arti-

able on the LRC web site,) that allows anyone to

response seems to make tailored light applica-

ficial light extending daylight hours since fire was

evaluate sources at any illuminance level. The

tion for a desired lighting effect impossible.” The

discovered, making artificial light as much a part

spreadsheet also provides an opportunity for

CIE memo also asserts that while there may be

of our existence as the sun. What is known is that

entering SPD data from any source for individual

“low-hanging fruit” from creating lighting input

SPD’s and illuminance levels are critical factors,

custom comparison. This is news anyone can use

into the newly discovered ipRGC’s (non-visual

which may or may not relate to CCT directly. The

now, and correlates with the NIH manuscript.

ganglion cells now referred to as “circadian

false assumption that high CCT products always

receptors”,) there is a need for clarification and

deliver significantly more light in the circadian re-

manipulate circadian cycles is a fe de compli. The

quantification. This is being addressed by techni-

sponse efficacy region (380 to 625nm with a peak

complexity of applying lighting to purposefully

cal committees at the CIE (TC 3-46) as well as the

at 484nm, per Berson, et al, 2002) is also noise.

manipulate human non-visual response is ad-

IES. This is news, indicating there is more that

Numerous studies indicate that high CCT alone

dressed in the CIE memorandum “CIE Statement

must be understood.

does not guarantee a desirable SPD content. The

This is not to say that application of light to

on Non-Visual Effects of Light”, which states “…

The supposition of humans evolving under

CIE addresses this when it states: “Among the few

non-visual responses are subject to complex sig-

daylight indicating a need for artificial light to

points of general agreement is that the non-visual

nal processing in the central nervous system and

mimicking daylight characteristic, mainly based

effects of light exposure depend on the spectrum,

influenced by as-yet-unresolved interactions of

on CCT—is noise. All artificial light sources differ

intensity, duration, timing and temporal pattern

photoreceptive units. The missing understand-

significantly from daylight (even high CCT sourc-

(light history) of the light exposure.” Note that

ing of the input-output characteristics between

es), and general illumination levels are a fraction

CCT is not mentioned, but spectrum is.


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Architectural SSL - February 2017  

Chronicling the Advancement of LED and Solid-State Lighting in the Built Environment.

Architectural SSL - February 2017  

Chronicling the Advancement of LED and Solid-State Lighting in the Built Environment.