What is Melanopic Daily Exposure Ratio (M-DER)?

Melanopic light brings us wellness 

In our modern world, artificial lighting has become an integral part of our daily lives. However, not all artificial light is created equal. The type and quality of light we are exposed to can significantly impact our body’s circadian rhythm, which in turn affects our overall health and wellness1. Natural sunlight is the primary driver of our circadian rhythm, with its varying intensities and wavelengths throughout the day signaling our bodies when to wake, be alert, and sleep.2 Modern lifestyles, with extended exposure to standard electric lighting and reduced exposure to natural light, often result in circadian misalignment and subsequent problems including fast occurring changes like energy, focus, and mood, and long term effects like sleep disorders, depression, obesity, diabetes, and cardiovascular diseases. So, fundamentally, you need the right type of light at the right time of day and night to keep a strong body rhythm alignment. But how?  

Seeing through the light 

Let’s face it. A quick scan around the room shows you that inside light basically looks the same. It lights the space. How would I know how ‘natural’ the light is? It really comes down to knowing how much blue-sky light is present to drive circadian rhythms. This is not as difficult as it seems. Two such measures adopted by the International Commission on Illumination (CIE TN015:2023) that are useful in assessing healthy light are: 

Putting a number on healthy lighting: The Melanopic Daylight Efficacy Ratio (M-DER) 

M-DER is a useful measure because it describes how effectively a given light source stimulates the human circadian system compared to natural daylight. Since daylight is the gold standard for circadian stimulation, M-DER provides a way to compare artificial lighting with its natural counterpart in terms of melanopic effectiveness.  

A higher M-DER indicates that a light source is more effective at stimulating the circadian system relative to its visual brightness. This is important because traditional lighting, designed mainly for visual tasks, often lacks the spectral quality needed to support healthy circadian rhythms.   

Figure 1.  Various sources of light and their measured Melanopic to Photopic Ratio (M-DER).  

 Standard lighting: Too dim for the day, and too bright at night.  

What’s surprising about most indoor light is how adequate it seems to be for its job: Illumination; accents; mood colors; and yet, a quick review of published measured melanopic ratios tells us a very different story about health. Figure 1 shows various standard light sources on the range of M-DER values. Natural light from sun and sky typically are around 1.00 and the recommendation is to thus have at least that value during day when you are inside.1 Notice how most electric lighting falls way short at less than 0.75 M-DER. Even common personal SAD light therapy lamps with their intensely, uncomfortably bright light are mostly at or less than 1.00. What’s needed is general lighting that can achieve or exceed 1.00 to maximize our normal, passive indoor exposure to healthy melanopic light.  

So, are these dual daytime melanopic lighting recommendations unreachable? Are the vast majority of us doomed to spend the 93% of our lives working/relaxing/sleeping indoors3 under spectrally unhealthy light? The answer to our earthly problem actually came from outer space.  

SkyView™ Circadian "Human" Lighting: High M-DER 

Originally designed to help orbiting astronauts stay healthy while experiencing day/night changes every 90 minutes, SkyView circadian "human" lighting technology is specifically engineered to support and enhance circadian rhythms by incorporating high M-DER values but at compliant energy loads (0.4 W/sqft).  

SkyView lighting is designed with a spectrum that closely mimics natural daylight, especially in the blue-light range that is crucial for ipRGC activation. This ensures that the light effectively stimulates the circadian system, promoting alertness during the day and facilitating better sleep at night. The high melanopic daylight efficacy ratio of SkyView lighting means that it provides strong circadian stimulation without the need for excessively bright light. This is particularly beneficial in environments where bright light might not be desirable or feasible, such as offices, schools, and healthcare facilities. By achieving a high M-DER, SkyView lighting ensures that users receive the necessary circadian stimulus equivalent to being outdoors in natural daylight, even while indoors. This helps maintain a robust circadian rhythm, contributing to overall health and well-being.  

For interior lighting design: know your M-DER 

Organizations like the WELL Building Standard and the International WELL Building Institute (IWBI) use M-DER as a criterion for lighting that supports human health. M-DER helps lighting designers assess how well artificial lighting supports circadian rhythms, which promotes alertness, energy, and mood for a healthier, more productive work environment. Since natural light from windows and skylights have design, seasonal, and weather limitations, the use of high M-DER light can effectively and easily ensure healthy light equity regardless of the architecture.  

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