Why circadian lighting? Part - 1

• Challenge of conventional lighting

The most significant problem from conventional lighting is the unreasonable performance for the human biological clock system. During the daytime, when the lighting design always focuses on horizontal lux but ignore the non-visual effects of human; at night, the situation could be even worse because too much melanopic lux affects sleep, or shortage of visual lux then generate the safety risks.

• Theory of circadian lighting

The theory of circadian lighting is based on the response of ipRGCs (Intrinsically Photosensitive Retinal Ganglion Cells) from the light. Unlike V(λ), the ipRGCs sensitivity peaks at around 480nm-490nm, which means our circadian system perceives the light in a different way than eyes (Figure 1).

The response of ipRGCs from the light affects the melatonin secretion directly then our circadian rhythm system, and the melatonin secretion is dynamic during a daily rhythm (Figure 2), which requires the circadian lighting should follow the theory. A circadian lighting product or solution does not have to be dynamic, but it must have a clear purpose, that is the most significant difference than the conventional lighting which is just for illumination.

In addition, circadian lighting theory measures the vertical lux (Ev) because ipRGCs exist in retina and perceive the lighting from the vertical angle, therefore the measurement always traces the human eyes position (Figure 3) – that is the true human-centric lighting principle.

Circadian lighting should be a comprehensive solution achieving both visual comfort and non-visual health with the same level of importance, none of which should be compromised.

• Metrics of circadian lighting

With the specific purpose beyond just illumination, circadian lighting is very related to ipRGCs response, therefore, besides the general lighting metrics like lux, color temperature, CRI…circadian lighting includes more metrics for non-visual biological lighting factors.

1.       Melanopic/Photopic Ratio (M/P, MR).

M/P is a specification of the lighting fixture (or the light source) which is determined by the spectral power distribution, it measures the ratio of how much light is involved between the non-visual ipRGCs sensitivity and V(λ). Higher M/P means this light is easier to achieve a strong circadian stimulus effect (also depending on the lighting design).

2.      Equivalent Melanopic Lux (EML).

EML = M/P × Ev, it indicates how much of the visual brightness is effective for the circadian stimulus. Higher EML means a stronger circadian stimulus lux to the eyes.

3.      Melanopic Daylight Efficacy Ratio (m-DER).

Same as M/P, m-DER is the specification of the lighting fixture (or the light source) which is determined by the spectral power distribution, it measures the ratio of how much light is involved between the non-visual ipRGCs sensitivity and V(λ) compared to the Daylight. Higher m-DER means this light is easier to achieve a strong circadian stimulus effect (also depending on the lighting design).

4.     Melanopic Equivalent Daylight Illuminance (m-EDI).

m-EDI = m-DER × Ev, it indicates how much of the visual lux is effective for the circadian stimulus compared to daylight. Higher m-EDI means a stronger circadian stimulus lux to the eyes.

5.      Circadian Stimulus (CS).

CS evaluates directly if the lighting environment brings strong/weak circadian stimulus effect. 

These metrics could be difficult to understand the algorithm mechanism, but the principle is pretty simple and straightforward and relevant organizations also provide references on specific values should be achieved in different scenes.

Applications for circadian lighting

Circadian lighting is adaptable everywhere human lives and thrives, but it can be more commercially effective and faster to be applied in some specific applications.

Hotel

• For cozy environment building with circadian comfort.
• Effective night light supplies enough visual brightness but never disturb the sleep.

Healthcare center

•          Circadian lighting for the guests who have to spend most of their time indoors.

•          Treatment for elder guests with more disordered circadian rhythm than youngsters.

•          Effective night light for enough visual brightness, avoiding falling down without disturbing circadian rhythm.

Hospital

•          Full-time circadian lighting solution provides necessary condition for the patients who have to spend most of their time in inpatient ward.

•          Personalized circadian lighting recipes for patients with different circadian cycles.

 Office

•              Circadian lighting for productivity and concentration of the employees during working time. 
•    Provide dynamic lighting conditions for employees’ wellbeing and satisfaction.

 

School

•          Circadian lighting for healthy shifts between learning and relaxing in the school.
• Protect teens’ circadian rhythm during growth.