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Radiometry and Photometry
Published in Antoni Rogalski, Zbigniew Bielecki, Detection of Optical Signals, 2022
Antoni Rogalski, Zbigniew Bielecki
The units as well as the names of similar properties in photometry differ from those in radiometry. For instance, power is simply called power in radiometry or radiant flux, but it is called the luminous flux in photometry. While the unit of power in radiometry is the watt, in photometry it is the lumen. A lumen is defined in terms of a fundamental unit, called candela, which is one of the seven independent quantities of the SI system of units (meter, kilogram, second, ampere, Kelvin, mole and candela). Candela is the SI unit of the photometric quantity called luminous intensity, or luminosity that corresponds to the radiant intensity in radiometry. Table 1.1 lists the radiometric and photometric quantities and units along with translation between both groups of units.
Lighting
Published in Stephen A. Roosa, Steve Doty, Wayne C. Turner, Energy Management Handbook, 2020
Eric A. Woodroof, Stan Walerczyk, Fred Hauber
Candela: Unit of luminous intensity, describing the intensity of a light source in a specific direction. One candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1,012 Hz and has a radiant intensity in that direction of 1/683 watt per steradian.
Understanding Light:
Published in Michael Stiller, Quality Lighting for High Performance Buildings, 2020
A further discussion of brightness, luminance, and illuminance will follow, but first let’s talk a little more about the light coming from our luminaire and source. The overall light coming from our luminaire, the lumens, can be further defined as candelas, or candlepower. A candela is really a measure of the concentration of lumens in a particular direction. To use our previous examples of a table lamp and a directional track light: though the number of lumens might be the same, when they are concentrated into a narrower beam by the track light, the candlepower, or the number of candelas, will be greater in the direction of that beam than when they are projected in an omnidirectional pattern, or a greater number of directions, around the room. Candlepower is a constant measurement, and does not change with distance. Even as the light will spread over distance, the number of lumens, and therefore candelas, coming from the source in that particular direction will remain the same.
Effects of neighbourhood morphological characteristics on outdoor daylight and insights for sustainable urban design
Published in Journal of Asian Architecture and Building Engineering, 2022
Illuminance level (E) refers to the luminous flux per unit area of visible light (lumens, symbol: lm)4One lumen (1 lm) is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian (1 cd). (Eq. 1), which represents the intensity of illumination on a given surface and is denoted by lux (symbol: lx). 1 lx is equal to 1 lumen per square meter (l lx = 1 lm/m2) (Fotios 2017). When a given surface is illuminated by multiple light sources simultaneously, the total illuminance of the surface means the sum of the illuminance generated by each light source. The horizontal illuminance level (HIL) of the site surface determines the adaptation of the eyes in the field of vision and serves as a visual background to highlight the target object. At present, HIL is a widely used lighting parameter in indoor and outdoor daylighting environment design (CIE 2000).
Evaluating asphalt pavement surface texture using 3D digital imaging
Published in International Journal of Pavement Engineering, 2020
Asphalt mixture surface generally exhibits Lambertian reflectance, which is a property defining an ideal diffusely reflecting surface (Ikeuchi, 2014). The asphalt mixture surface’s luminance is nearly isotropic, and the luminous intensity obeys Lambert’s cosine law as shown in Equation (1). Lambert’s cosine law model for diffuse reflection is extensively used in shape recovery techniques such as photometric stereo and shape from shading (Ikeuchi, 2014).where is the intensity of the diffusely reflected light (surface brightness), in candela (cd); is the intensity of the incoming light, in candela (cd); is the albedo; N = , the surfaces normal vector, where = and q = , is the asphalt mixture surface function; , the normalised light-direction vector, pointing from the surface to the light source, where and are shown in Figure 1.
Comparison of Metal Plaque Formation and Metal Accumulation in Reeds Cultured in Acid Mine Drainage Solutions and Soils
Published in Soil and Sediment Contamination: An International Journal, 2019
Rhizomes of common reed P. australis were purchased from Lorenz’s OK seeds, LLC (Okeene, Oklahoma). They were initially grown in commercial potting soil (Micracle-Gro lawn products, Inc) in pans (45 cm×25 cm×7.5 cm). Two centimeters of potting soil were placed in the bottom of each pan. This was followed by the rhizomes and another 2.5 cm of potting soil. The rhizomes were cultured in a greenhouse under natural light conditions with luminance of light ranging from 1000 to 60000 candela per square meter (Cd/m2). The average temperature of the greenhouse was 22°C and the humidity was 50%. Five hundred milliliter distilled water (DI) were sprayed into each pan every day to maintain the soil moisture. After 30 days of growth in the potting soil, seedlings and rhizomes with similar biomass were transferred into spiked soil or hydroponic solutions to initiate experiments. Prior to being transferred, the rhizomes of the reeds were rinsed with DI water to remove the attached potting soil.