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Understanding Light:
Published in Michael Stiller, Quality Lighting for High Performance Buildings, 2020
Illuminance is the amount of light per unit area that is projected onto a given surface, while luminance is the amount of light per unit area that is emitted or reflected back to the viewer from a given surface. Illuminance has both a metric and imperial expression. The metric expression, lux, is the measure of the amount of light, or number of lumens, that falls onto a surface the size of a square meter; and the imperial expression, foot-candles, is the amount of light that falls onto a surface the size of a square foot. Both the illuminance on a surface and the luminance of a surface will vary as the distance is varied between the surface and the source of light, as they are both dependent on the concentration of light, or lumens, that falls that surface. As we have demonstrated with our flashlight, the number of lumens falling on a given area will decrease as we move our light source farther from the object being lit, and the beam, made up of a constant number of lumens, spreads out to cover a greater and greater area. The luminance of a surface will also be affected by other factors, namely that surface’s translucence (in the case of back-lit materials), reflectance (or color) and specularity (or glossiness).
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Published in Barney L. Capehart, William J. Kennedy, Wayne C. Turner, Guide to Energy Management, 2020
Barney L. Capehart, William J. Kennedy, Wayne C. Turner
A light meter is needed to measure illuminance levels. An inexpensive digital light meter is practical and rugged for screening lighting levels and determining relative values. A self-calibrating digital light meter (photometer) is very useful to get fast, accurate, and repeatable measurements. Using a lightmeter, the auditor should record light intensity readings for each area and task of the facility.
Energy Audit
Published in Anil Kumar, Om Prakash, Prashant Singh Chauhan, Samsher, Energy Management, 2020
Anil Kumar, Om Prakash, Prashant Singh Chauhan, Samsher
Illuminance and light distribution have a crucial influence on performance and occupational safety. The luminous power (lumen) between a light source and illuminated area is measured using the lux (lx) unit. The illuminance is precisely one lux when luminous power of one lumen (lm) homogeneously illuminates an area of one square meter. A lux measuring instrument is referred to as a “lux meter” or also as a “photometer.” Photo cell senses the light output and converting it to impulses of electricity, which is said to be lux. Few lux meters have internal memory or a data logger for recording the measurements. Lux meters with data loggers are very much useful since their cosine correction of the angle of the incident light. These lux meters can store values since it has memory and software in addition to different interfaces. It helps in transferring data to a computer, where further analysis can take place.
Linear regression based indoor daylight illuminance estimation with simple measurements for daylight-linked lighting control
Published in Journal of Building Performance Simulation, 2023
Hyeong-Gon Jo, Seo-Hee Choi, Cheol Soo Park
Recently, many lighting control schemes, which are divided into daylight-based lighting controls (DLCs) and occupancy-based lighting controls (OLCs), have been suggested to save lighting energy in buildings (Bakker et al. 2017; Wagiman et al. 2020). These schemes save lighting energy by turning off or dimming unnecessary luminaires in rich daylight or absence-of-occupancy environments. The schemes consist of two processes: detecting luminaires and controlling luminaires. In DLC, detecting luminaires means determining the daylight illuminance of points to provide sufficient lighting for these points (Mahdavi 2008). Excessive illuminance over the target illuminance is deemed to be unnecessary and accordingly a lighting energy-saving opportunity. In this regard, daylight information is crucial for successful DLC applications.
An underwater lighting and turbidity image repository for analysing the performance of image-based non-destructive techniques
Published in Structure and Infrastructure Engineering, 2018
Michael O’Byrne, Franck Schoefs, Vikram Pakrashi, Bidisha Ghosh
Lighting also plays a pivotal role for achieving good visibility. Ambient light may be sufficient for near-surface inspections; however, it is unlikely to be sufficient at greater depths at which point artificial light will become necessary. Three light levels were used: 100 lux, 1000 lux, 10,000 lux. To put this in perspective, the approximate level of light, or illuminance, on a very dark overcast day is 100 lux, a moderately overcast day is 1000 lux, and full daylight (not direct sunlight) is 10,000–25,000 lux (Schlyter, 2009). The lux is the SI unit of illuminance that measures the intensity of light that strikes a surface, as perceived by the human eye. It is similar to irradiance, which has units of watts per square metre, but with the power at each wavelength weighted according to a standardised luminosity function that is based on a model of human visual brightness perception. The illuminance can be measured using a lux meter, which are readily available and portable. A specimen from each section of the repository is shown under varying lighting and turbidity levels in Figures 5–7.
NRG4-U: a novel home energy management system for a unique loadprofile
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Asimina Dimara, Vasileios Georgios Vasilopoulos, Stelios Krinidis, Dimitrios Tzovaras
To deescalate the error, another method is also used to estimate the visual comfort. The European Lighting Standard ‘EN12464-1’ (E 2002) endorses a scale of illuminance level in lux as depicted in Figure 3. As stated both in ‘EN12464-1’ (E 2002) and in (Levels 2020) the appropriate illuminance level in a room is 500 lux. Furthermore, the indoor sensors usually measure from 0 to 1024 lux (e.g., EltaKo, Sensor TAP-31, Fibaro, EnOcean). Therefore, the ‘EN12464-1’ is fitted to a [−3, 3] scale, where −3 (very dark) is set to 0 lux, 0 (neutral) is set to 500 lux and 3 (very bright) is set to 1024 lux as depicted in Figure 4.