This paper presents a theoretical framework for incorporating the non-image-forming effects of light into daylighting design in the built environment. The framework includes human performance indicators to measure the magnitude of the non-image-forming effects of light as well as light factors to quantify these effects. In addition, architectural (daylighting) design parameters are included to control the magnitude of the light factors reaching indoor environment. To assess the magnitude of the non-image-forming effects of light in daylighting design process, threshold values for every light factor are discussed. A distinction is made between luminous and temporal characteristics of every light factor and the application of their thresholds in daylighting design process. The proposed framework enables stakeholders in the field of daylighting to incorporate the non-image-forming light requirements in design and to evaluate the potential of indoor spaces with regard to these requirements.

Implementing non-image-forming effects of light in the built environment

Daylight and lighting seem to be a key tool for people’s well-being, however, there are no specific and agreed recommendations that address both photopic and melanopic aspects in educational environments. The present work analyzed melanopic light in four teaching environments considering photopic indoor lighting, daylight depending on the window orientation, location of the observer in the room, and their line of view. The facade direction, daylight at 11.00 a.m. for six months from October to March, and the characteristics of each classroom, such as reflectance of the surfaces, location of the luminaires and their spectral and spatial power distributions, or calculation points affecting the melanopic light reaching the corneal vertical plane of a hypothetical control observer were studied. For this evaluation, classrooms were experimentally treated and simulated using DialuxEvo software, and the computer-generated values resembled the experimental values. Once the study was performed, an improvement proposal, based on LED lighting, was made to optimize the classroom lighting considering the melanopic requirements, which we ensured that users who passed through these classrooms had an adequate amount light at any time of the day. Our results simplify to the greatest lighting projects and enable designers to carry out optimized evaluations of specific environments from both the photometric and circadian perspectives.

Analysis of Photopic and Melanopic Lighting in Teaching Environments

Light affects many aspects of human physiology, through the non-image-forming (NIF) pathway. To account for this pathway, lighting design simulation tools need to combine several luminous and temporal factors to predict how architectural and lighting design decisions affect eye-level light exposure. Based on a systematic literature review, containing 55 journal and conference papers, the state-of-the-art towards implementing lighting beyond vision in computer simulation workflows for building design is presented. The review shows that, while interest in simulating the NIF effects of light on people is increasing, there is not a common method to perform these simulations. Gaps were identified in the currently available simulation workflows in relation to metrics, software and approaches for predicting NIF effects of light in the context of the building design.

Simulations of non-image-forming effects of light in building design: A literature review

Apart from the visual effects, light can also affect the human non-visual system, which includes a wide range of functions such as hormone secretion, alertness, mood etc. The non-image forming effects occur because light affects melanopsin, a photosensitive protein present in the receptive domain of retinal ganglion cells. These cells are responsible for generating nerve impulses that regulate the secretion of two hormones, cortisol and melatonin. Low-wavelength light at 460-480 nm inhibits melatonin secretion and activates brain activity. Aim of this paper is to create a sustainable and human centric luminaire suitable for office installations that will regulate the biological rhythm of the occupants and has the minimum environmental impact. The luminaire’s light source emits variable spectrum, with a collated colour temperature varying between 2700K and 6500K. For a 500K step of colour temperature values, the appropriate human centric lighting metrics are calculated: Equivalent Melanopic Lux, Melanopic Daylight Equivalent Illuminance, Circadian Stimulus. The development of the human centric luminaire considers not only the metrics of human centric lighting but energy efficiency and visual comfort as well. Conclusively, the proposed luminaire can provide a holistic approach to lighting design so as to integrate both visual and non-visual effects and produce sustainable and environmentally friendly lighting.

https://iopscience.iop.org/article/10.1088/1755-1315/1123/1/012039/pdf

Design and Development of a Sustainable Environmentally Friendly and Human Centric Luminaire

The indoor environmental quality is very significant as humans spend more than 90% in indoor space. Biophilic design of indoor spaces has become a popular approach in the design of indoor building spaces sector using green walls, especially in offices, leisure and hospitality facilities. So far there exist neither guidelines with the proper Spectral Power Distribution (SPD) except for agricultural applications or intensity levels of lighting nor the proper spectral indices to transform the photopic illuminance to a new type of photometric quantity for biophilic design. On the other hand, for human centric lighting the Equivalent Melatonin Illuminance is already introduced. The aim of paper is to define the appropriate lighting conditions, not only for humans, but also for interior plants. A new metric was introduced for the biophilic design named Equivalent Photosynthetic Illuminance. The new metric was examined for two human-centric lighting luminaires and compared with the corresponding human centric lighting metrics in order to create a lighting design guide for energy-sustainable, biophilic and human-centered lighting. The different SPDs highlighted the counterbalancing impact(s) of such luminaires, between biophilic and human-centered design. The differences concerning their impact on interior lighting design were identified with regards to energy consumption, meaning that the compliance of the lighting conditions to both humans and plants results to higher energy consumption. Depending on the SPD and luminous efficacy of artificial lighting, the additional power density for proper planning of biophilic design can vary from 23.5W/m2 to 52.4W/m2 in the areas in which are applied. 

Τhe effect of artificial lighting on both biophilic and human-centric design

The evaluation of both visual and nonvisual effects from the spectral power distribution (SPD) of outdoor light is critical in lighting design. The dome-light SPD characteristically changes continuously depending on the seasonality, orientation, altitude of the sun or hour of the day. Traditional photopic parameters, such as the illuminance, luminance or correlated colour temperature (CCT), have been widely studied, but presently, there is no melanopic measurement or evaluation method. This article discusses the processes involved in establishing a simple method to determine the SPD of daylight and solar radiation over the skydome in a location to accurately account for the effects of both photopic and circadian levels around a location. Once per month for one year, natural daylight was spectrally measured in the city of Zaragoza (Spain); radiometric and photometric characteristics were analysed by season; and circadian effects were calculated in terms of standard parameters described by the Commission International de l’Eclairage (CIE), factors recommended by normative and scientific backgrounds. Finally, we suggest that the best parameter is the melanopic versus photopic irradiance ratio, which achieves reliable results at simplifying and correlating calculations.

Silvia Ezpeleta

Papers

Analysis of Photopic and Melanopic Lighting in Teaching Environments

Evaluation of Visual and Nonvisual Levels of Daylight from Spectral Power Distributions Considering Orientation and Seasonality