Human-centric Ligting

Prof. Dr. Banu Manav

The primary purpose in lighting design is to offer energy-efficient solutions, keeping up pace with up-to-date approaches to lighting technology, to ensure visual comfort requirements for users.

In this line of vision, the concept of lighting quality has been contextualized with human-centric lighting, biodynamic lighting and circadian rhythm (CS) in time through historical perspective. All
these concepts are fundamentally based upon developing system suggestions to ensure visual comfort of users.

The concept of human-centric lighting is a system design and concept that queries throughout design process what kind of an artificial ambiance should be offered to users, in harmony with their visual comfort requirements and biological rhythm. Although certain measurable quantities such as the level of irradiance, color temperature of light source, color rendering indices and luminosity contract are defined in lighting design, the mood in response to physical environmental effects varies by individuals. 

    Far from being just a physical stimulus, light is also an energy that impacts our biological rhythm, hormone levels, psychology, cognitive functions and ability to perceive while balancing our biological clock (see Figure 1). Therefore, today’s lighting design is remarkably under the influence of circadian rhythm, biological clock etc. Even if coded genetically, circadian rhythm is readjusted with daylight on daily basis. Insufficient amount of daylight during day leads to the lack of serotonin production, which eventually causes insufficient production of melatonin during night. Melatonin is a hormone secreted in the darkness and thus, those who are exposed to high level of illuminance and cold light at night, fail to secrete sufficient amount of melatonin. In consequence, the individual may start the day in a tired mood, giving rise to many problems including underperformance and distractibility and extended disturbance of sleep also triggers many issues in immune system finally leading to occurrence of certain diseases. 

The discovery of a new photoreceptor other than cone and rod cells at the beginning of the twenty-first century and its correlation with pituitary gland have played a significant role in studying such invisible effects of the light. The scientific studies in medicine as well as technological advancements are reflected on lighting design in an attempt to offer an optimum solution for human health and visual comfort. Studies reveal
that lighting design should support the systematic functioning of our body in a methodical manner. For example, the use of screens such as laptops, mobile phones, computers etc. at late hours impairs sleeping quality. The wavelength of the light emitted from such devices decreases the secretion of melatonin and extends sleep onset latency. In a like manner, it is widely suggested to design a time-controlled lighting system, which offers an artificial lighting system design in tune with circadian rhythm depending on the changes in color temperature and the level of illuminance throughout the day. When applied at 5000-6000K in the morning, 4000-5000K at midday and 3000K at eventide, the change in color temperature yielded positive results in performance when applied in offices and classrooms (See Figure 2). 

In conclusion, it can be said that human-centric lighting is not merely designing and applying an
automation system. With reference to the rhythm of balance in nature, the right light should be organized at the right time in accord with our biological clock, and the level of illuminance, color
temperature of light, the angle of sight, level of cylindrical illuminance, and luminance distribution should be taken into consideration in developing a solution offer for lighting while maintaining the balance of body’s biological clock.

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