Natural Light is the great part of interior architecture design. Architect like to use windows and daylights to bring the daylighting into buildings. There are some great benefits of daylighting:
1) reduce overall artificial lighting consumption and energy cost. Most buildings incorporated daylighting can achieve overall energy savings from 15 to 40 percent.
2) daylighting is great for humans’ well-being and productivity. The great balance of artificial lighting and daylighting can create a human centric lighting that will support the people’s health needs.
How to incorporate daylighting into lighting design and make the best use of natural light?
First, the architectural design and construction of buildings can take advantage of natural light by considering building orientation and adding enough windows, skylights and roof lights and shading devices to control glares.
Second, for commercial buildings, the California Lighting Technology Center (CLTC) published a best practices guide for designing daylight harvesting lighting control systems. It is a great resource for design ideas of building fenestration: skylights, atria, tabular daylighting devices, windows, clerestories. It also introduces shading strategies and technologies from exterior shading and interior shading to between glass panes shading system. It definitely won’t miss the interior and lighting design. Interior design parameters such as reflectance of interior surfaces even furniture are very important for daylighting performance. The layout of luminaires and design of lighting control system are the key lighting design parameters.
Interior lighting usually includes different layers of lighting: Ambient lighting, task lighting, accent lighting and decorative lighting.
Lighting controls for daylighting to support better daylight harvesting include use high efficacy solid state lighting fixture that can be stepped switching or continuous dimming beyond standard ON/OFF switching. There is also other control strategies to control the daylight amount in the daylit zones by using astronomical time clock to easily switching or dimming lights at specified times. The control strategy can also use photosensing (photosensors) to determine the exact available daylight to control lighting switching and dimming.
For photosensing, it divides into open-loop sensing and closed loop sensing. Open-loop sensing can be implemented with either photosensors placed either outdoors or indoors facing toward windows or skylights, but it can result over-dimming due to it does not reflect indoor daylight levels.
Closed-loop sensing uses photosensor signal to determine daylighting level which is affected by the controlled lighting and natural light. The sensor used in closed loop should place so that it can detect both daylight and artificial light. It can use constant set point algorithm to adjust the artificial lighting level to keep the closed loop sensor maintain at specific signal.
The more advanced control algorithm can using sliding set point which is applicable to both open-loop and closed loop system. It generates control signal to control ballast or drivers of light source that proportional to photosensor signal, between the defined range by Offset point and Sliding set point. When using only a single photosensor in closed loop – sliding set point control, it can not tell the difference was caused by daylight changes or other transient disturbances from geometry and/or reflectance within the interior environment.
Dual loop and redundant sensing approach uses both open and closed loop sensing to reliably determine true daylight changes. The closed-loop sensor is used to monitor light level in the space, while the open loop sensor is used to determine closed loop photo sensor signal was produced by daylight changes. This type dual loop sensing approach can be used in spaces with windows and clerestories. Dual loop has proven to be more reliable and achieve more energy savings. Redundant sensing is equivalent to dual loop control but relies on use of multiple closed loop control sensors to increase reliability of sensing daylight changes.
With adoption with wireless daylight sensor that can easily integrated into fixtures, it will be much easier to implement control algorithm and lighting configurations.
