Daylight harvesting

The Sun has ever been used by humans being as a main source of light. All the live organisms evolved by natural light, that is why human biology is highly associated with sun energy. Light is not only used for perception of matter, what we call vision, but also for main biological function, called circadian rhythm.

Artificial light systems which also use daylight are striving to balance the amount of electrical light needed for appropriate area illumination to reduce the power consumption. It can be done with light control techniques that can dim or switch the electric light in response to changing amount of daylight. 

Changing the daylight intensity and spectral composition is critical to our health as it adjusts our biological clock and related functions such as alertness, hormone levels and body temperature (Fig. 1) 

Fig.1  Circadian rhythms showing changes in cortisol, melatonin, alertness and body temperature throughout the day

The systems for reading the amount of daylight in rooms are set to maintain the recommended level of light. This level of light will vary, depending on the needs and use of the designed space.

Daylight sensors measure natural light in relation to specific lighting setpoints and gives signal to the electronics to adequately minimize the power of the electric light. 

Lamps installed in the room will shine with different intensity, depending on the distance from the natural light sources (Fig. 2) 

Fig.2  An example of how to set the lamp power  depending on the distance from the window. 

The positioning and grouping of the luminaires (Fig. 3) for controlling when using daylight are very important as they have a significant impact on achieving the potential savings from overall design strategy. In the case of skylights, luminaires are mounted between the skylights and are usually inspected in groups that are determined by the lighting needs of the room. 

In window and wall applications, lighting fixtures are typically arranged in controllable groups parallel to walls with windows, as daylight levels drop significantly depending on the distance from the windows.

The term ”Daylight Harvesting“ is becoming the standard in lighting, sustainable architecture and the active daylight industry.

Fig. 3 Arrangement of groups depending on the distance from the windows. 

Position of the windows in the building must be designed in way to avoid admitting direct sunlight onto the visual task surfaces or directly into the eyes of the users. Glare should be minimized through the use of roller shutters or blinds. Correct and highly efficient use of daylight in a project goes beyond the simple installation of the above-mentioned components. Daylight requires an integrated design approach, as decisions about the building’s form and location, climate, building components (such as windows and skylights), lighting controls and lighting design criteria must be considered to reach its full potential.

The design of both buildings and systems for the use of daylight is not only about providing enough light in a given room, but also about design that will not introduce unwanted side effects.

The use of daylight to illuminate workplaces can also bring significant savings by reducing power consumption. In commercial buildings, they can be as high as 35 percent. These savings depend both on the correct placement of light sensors in the building, the use of energy-saving LED light sources, and to a large extent on the geographic location or design of the building 

You can read about daylight zones in the recommendations for energy efficiency in buildings.

These zones are building areas where daylight collection is possible thanks to the close proximity to window openings and floodlights. 

There are three types of daylight zones:  
• Primary Sidelit Daylit Zone
 Daylight area directly adjacent to one or more windows
• Secondary Sidelit Daylit Zone:
an area of daylight not directly adjacent to the window, which still receives daylight through its proximity
• Skylit Daylit Zone:
an area of daylight illuminated by one or more skylights

Correct use of daylight should not only focus on its quantitative but also qualitative importance.

Therefore, already at the design stage, unnecessary reflections of high brightness should be eliminated by eliminating surfaces that cause light reflections. Thanks to the controlled introduction of daylight into the interior of the building, we can adapt to a high level of luminance, as long as this light is evenly distributed. Light that reaches the visual task surface indirectly will provide a better quality of illumination than light that comes directly from a natural or artificial source.

The purpose of efficient daylighting is not only to ensure adequate levels of illuminance, but also to maintain a comfortable and pleasant atmosphere. Glare or excessive brightness contrast in the field of view is an aspect of lighting that can cause discomfort to users.

The contrast of brightness levels can also be a desirable phenomenon in space for visual efficiency. Correct lighting uniformity can lead to boredom and lack of attention. Introducing rooms with a different contrast in buildings may cause our curiosity, interest, and thus, user activity. These types of treatments are used during recreational events.

Norbert Chrzanowski

Head of Research & Development  LEDline®

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