Lighting without paying: Once upon a time, the light pipe

Statistically, Non-residential buildings are on average 40% more energy intensive than residential buildings. This fact has triggered much research aimed at exploring alternative energy sources for such buildings for lighting and heating purposes. In addition, there is pressure to limit the impact of buildings on energy consumption, specifically greenhouse gas emissions which are responsible for global warming. In fact, from a health standpoint, artificial lighting tends to suppress melatonin production, thus ensuring increased vigilance and therefore, an improvement in work performance. The harmful effect is occupants cannot be in a serene surrounding. Fortunately, the intake of natural light can balance this trend by ensuring a space of qualities both in production and in the occupant’s welfare.  Daylighting predates current technology and is a hallmark of any designer to have their structure naturally lit as much as possible for obvious reasons. Back in the 80’s, an innovative daylighting device was reported. The devise; a highly reflective light pipe, dubbed the Mirrored Light-Pipe (MLP), is comprised of multiple specular reflection conveyors. These modern gadgets allow daylight to be transported and distributed in dark rooms far from traditional openings while limiting heat transmission.

Existing literature highlights on the need to identify and study the climate in which the light pipe will be installed. Consequently, state-of-the-art experimental and numerical studies have been progressively conducted over the period from 1990 to 2019. Nonetheless, more studies are necessitated to understand the devise better. On this account, researchers from the University of La Reunion, France: Dr. Bruno Malet-Damour, Dr. Dimitri Bigot, Dr. Stéphane Guichard and Pr. Harry Boyer, proposed to learn more about the stock of experimental knowledge about the light pipe and contribute to the understanding. Their work is currently published in the research journal, Solar Energy.

In their work, various scenarios were studied, including: impact of the reflection coefficient of the area to be illuminated, presence of an anticyclonic dome, type of sky or the ideal position of a sub-dome deflector. Overall, state of the art on experimental and numerical results on Mirrored Light-Pipe were thoroughly reviewed for the period; 1990-2019, with a particular focus on the southern hemisphere.

The authors reported that the light distribution within the room was strongly related to the type of sky. It was also seen that in cloudy skies, the diffuser behaved like an orthotropic source whose diffusion followed a Lambertian law. Indeed, the light pipe acted as a black box. Further, the researchers noted that the profile of the indoor illuminance was similar to the profile of the outdoor. Additionally, in a clear sky, the observation was no longer valid. The indoor lighting became directional, linked to the position of the Sun. Lambert’s law was no longer valid.

In summary, the study concentrated on contributing to the experimental photometric study of Mirrored Light Pipes. Interestingly, in 2019, the study was the only published paper analyzing the performance of the light pipe in extreme situations of extreme sunlight conditions. In a statement to Advances in Engineering, Dr. Bruno Malet-Damour mentioned that they are currently working on a thermal experimental study that could lead to understanding the impact of the light pipe on indoor ambient conditions and the user thermal comfort in the tropical climate. Its objective is to demonstrate that visual comfort can be met with this type of device without impacting thermal comfort while reducing energy consumption. Moreover, in parallel with this publication project and to ensure a total understanding of the phenomena, Dr. Malet-Damour also seeks to understand the thermal, photometric, and physiological interactions of the human body with its environment. He confided to us that he is motivated for international collaborations on these promising subjects!