
2019.05.30
R&D WORKS Vol. 05
Next Generation Ambient Lighting
Sensory performance required for lighting fixture design
Improves the "sense of brightness."
光環境を評価するときに「明るさ感」という尺度があるのをご存じでしょうか。照度や輝度の高さと、明るく感じるかどうかは実は別もの。周りが暗いとより明るく感じるように、人の眼は環境に順応するからです。この「明るさ感」に基づいて照明器具を設計すると、実際の照度や消費電力が低くても、同じ明るさに感じられるようにデザインでき、省エネルギーになります。オフィス空間の光環境を最適化するために、「明るさ感」を向上させる器具を三菱電機照明とともに研究開発しました。

The index of "brightness"
When planning lighting, what is the basis for determining the brightness of a room? Generally, the illuminance on a desk is measured and used as an index. But is that enough? There is an idea that brightness should ultimately be set based on how people perceive it. The index at that time is the "sense of brightness of the space." It is a value that is corrected to see whether people perceive it as bright, taking into account contrast and other factors, based on the intensity of light reflected from each part of the room, that is, luminance. By creating a distribution map that divides the brightness perceived from objects into 13 levels from "very dark" to "very bright," and increasing the area that is perceived as appropriately bright, the "sense of brightness" increases, making it possible to plan lighting that both saves energy and improves the sense of brightness. This time, we focused on this "sense of brightness."
- The "brightness" is indicated by the NB value. The NB value is an index proposed by Professor Yoshiki Nakamura (Tokyo Institute of Technology). 1 indicates "very dark," 7 indicates "neither bright nor dark," and 13 indicates "very bright."

"Appears brighter and improves the sense of brightness"
The more yellow there is with a NB value of 7 to 8.5, the brighter the image appears.
What is a design that enhances the "perception of brightness"?
By improving the "brightness" of the environment, even if the illuminance above the desk is reduced from 500lx to 350lx, the space will not feel dark and will be sufficient for an office working environment. This will reduce power consumption and lead to energy savings. Therefore, we pursued a design that improves the "brightness" of grid ceiling lighting for offices.
The challenge was, "What kind of light distribution curve will give the right sense of brightness?" Traditionally, emphasis has been placed on light distribution on desks and walls, but it has become clear that it is also necessary to direct light toward the ceiling, which takes up a certain amount of field of vision. The result was that the light distribution had a ratio of 80% of the luminous flux downward and 20% upward. The "next-generation ambient lighting" was designed based on this light distribution.


Bottom: Next-generation ambient lighting. It saves energy while providing a sense of brightness throughout the room.
Cover shape creates a prism effect
The key feature of the "next-generation ambient lighting" is the cross-sectional shape of the transparent polycarbonate cover. The triangular cross-section of the cover acts like a prism to distribute light between the ceiling and downwards. A demonstration experiment was conducted to compare conventional lighting of 500lx (LED light source, 4000K) with next-generation ambient lighting of 350lx (LED light source, 4000K). By replacing conventional lighting with ambient lighting, the NB value of the 7-8.5 range rate increased from 7.7% to 8.9%. Meanwhile, power consumption decreased from 6.1W/m2 to 4.4/m2.

Co-developed with: Mitsubishi Electric Lighting Co., Ltd.
Developed products: "LED integrated grid ceiling lighting lens control type"
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Sensory performance required for lighting fixture design
Improves the "sense of brightness."

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Update : 2019.01.17