Uncovering the Spectral Microclimate of Indoor Spaces

and Spectral Light.

In modern times, we spend most of our days in indoor spaces, be it at home, at work or in public places. As such, the quality of indoor air and lighting conditions have become increasingly important for our well-being and health. The focus has been mostly on temperature and air quality, but the impact of light spectra has been largely ignored. However, recent studies show that the spectral composition of light can impact our hormones, circadian rhythms, and mood.

That is why it is important to characterise the melanopic/spectral microclimate of indoor spaces. The melanopic lighting is a branch of photobiology that deals with the impact of light on human non-visual responses such as the circadian system and melatonin secretion. This implies that light sources that usually are visually pleasing, might have an adverse impact on our health.

The scientific community has come up with a way to measure the impact of light on the human body by using the melanopic equivalent of the spectral irradiance (MEASI) metric. MEASI is the measure of the effectiveness of light on the circadian system, where different wavelengths of light correspond to a multiplier factor that indicates how much it could affect the circadian system.

The MEASI metric considers that the human eye perceives light differently from how the circadian system detects it. Conventional light bulbs can emit light that is similar in intensity to natural light during the day, but they usually lack in short-wavelength light, which is necessary for the regulation of the human circadian system. Short-wavelength light is mostly blue and purplish in colors, commonly found in morning sunlight.

As our days are filled with a multitude of activities, we must regulate our sleep-wake cycle properly, which is where indoor lighting enters the picture. Exposure to light during nighttime can result in sleep disruption and damage to one's natural rhythm, so it is important to control the spectral content of artificial lights in indoor spaces. The circadian-optimized indoor lighting must contain a full spectrum of colors that simulate sunlight, but accentuate the blue light in the morning and less of it at night to help promote healthy sleep patterns.

Given that most people spend roughly a third of their life in bed under artificial light, it is essential to focus on the quality of lighting in indoor spaces. This is where the concept of the "spectral microclimate" comes into play. Spectral microclimate is a term used to describe the collective melanopic spectral environment present within a given space over time. It could vary depending on factors such as occupants, schedules, and daylight availability.

Compared to other environmental factors such as temperature and humidity, lighting has often been overlooked. However, the spectrum of light can significantly impact our well-being. A recent study found that people who work in offices that have windows with a good view of outdoors are found to have lower levels of stress hormone cortisol by the end of the day compared to those who work in windowless offices.

It is important to note that too much exposure to light can have the opposite effect, leading to impaired circadian rhythms and health problems such as sleep disorders, metabolic dysfunction, and even cancer. Therefore, it is crucial to balance lighting in indoor spaces by controlling the intensity and color of light.

In conclusion, the melanopic/spectral microclimate of indoor spaces is critical to our health, mood, and productivity. The circadian rhythms dictate our biological clocks, and as such, we must regulate our exposure to light properly. Lighting is a crucial environmental factor that needs to be considered in indoor spaces, just like temperature and air quality. Through proper lighting, we can improve the conditions of our indoor microclimate and move closer to a healthier and more stable life.