Lighting Glossary

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[edit] A

  • Albedo The albedo of an object is the extent to which it diffusely reflects light from the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unitless measure indicative of a surface's or body's diffuse reflectivity. The word is derived from Latin albedo "whiteness", in turn from albus "white". The range of possible values is from 0 (dark) to 1 (bright).
  • Albedo feedback A climate feedback involving changes in the Earth’s albedo. It usually refers to changes in the cryosphere which has an albedo much larger (~0.8) than the average planetary albedo (~0.3). In a warming climate, it is anticipated that the cryosphere would shrink, the Earth’s overall albedo would decrease and more solar energy would be absorbed to warm the Earth still further.

[edit] B

  • Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed.

[edit] C

  • Candela The unit of measure for the intensity of light at the source roughly equal to the amount of light in any direction from the flame of a candle.
  • Color Rendering Index (CRI) is the ability of a light source to produce color in objects. The CRI is expressed on a scale from 0-100, where 100 is best in producing vibrant color in objects. Relatively speaking, a source with a CRI of 80 will produce more vibrant color in the same object than a source with a CRI of 60.
  • Color Temperature The overall color appearance of the light itself. When referring to a source as either "warm" or "cool" the Color Temperature is being discussed. Color temperature is expressed in units of Kelvin. Lamps range from 2100-7500 Kelvin. Lower color temperature (3000K) represents "warm" light, higher (4100K) represents "cool" light.
  • Civil Twilight is the time between the moment of Sunset, when the sun's apparent upper edge is just at the horizon, until the center of the sun is directly below the horizon.

[edit] D

  • Darkness is the percepted state of being dark or the absence of light.
  • Daylight or the light of day is the combination of all direct and indirect sunlight outdoors during the daytime (and perhaps twilight). This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected from the Earth and terrestrial objects.
  • Dusk The period of waning light from the time of Sunset to dark. Civil dusk is when the center of the sun reaches 6° below the horizon. This marks the end of the evening civil twilight, the point where artificial illumination is required to read outside. It can be confused with sunset, which is the daily disappearance of the sun below the horizon.

[edit] E

[edit] F

  • Floodlights are broad-beamed, high-intensity artificial lights often used to illuminate outdoor playing fields while an outdoor sports event is being held during low-light conditions.

[edit] H

  • High-definition video or HD video refers to any video system of higher resolution than standard-definition (SD) video, and most commonly involves display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/1080p). This article discusses the general concepts of high-definition video, as opposed to its specific applications in television broadcast (HDTV).
  • High intensity discharge (HID) lamp is a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the arc's initial strike. Once the arc is started, it heats and evaporates the metal salts forming a plasma, which greatly increases the intensity of light produced by the arc and reduces its power consumption. High intensity discharge lamps are a type of arc lamp.

[edit] I

  • lumen per square foot. Measured footcandles are sensitive to the distance from the source to the surface of measure (inverse square law) and the angle at which the light reaches the surface (cosine law).
  • Intensity The light emitted from a source. Intensity most often varies given the direction at which one views the source. Intensity does not vary with distance. A candle produces the same intensity in a given direction whether on a table in front of you or one mile away.
  • Insolation is a measure of solar radiation energy received on a given surface area in a given time. The name comes from a portmanteau of the words incident solar radiation. It is commonly expressed as average irradiance in watts per square meter (W/m2) or kilowatt-hours per square meter per day (kW·h/(m2·day)) (or hours/day). In the case of photovoltaics it is commonly measured as kWh/(kWp·y) (kilowatt hours per year per kilowatt peak rating).*Kilowatt Hour (kWh) The measure of electrical energy from which electricity billing is determined. For example, a 100-watt bulb operated for 1000 hours would consume 100 kilowatt hours, (100 watts x 1000 hours = 100 kWh). At a billing rate of $0.10/kWh, this bulb would cost $10.00 (100 kWh x $0.10/kWh) to operate over its life.

[edit] K

  • Kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale referenced to absolute zero, the theoretical absence of all thermal energy. So by definition, the temperature of a substance at absolute zero is zero kelvin (0 K).

[edit] L

  • Lumen The unit of measure for the light energy which flows in air. The total light output from electrical sources is expressed in lumens. A uniform source of one candlepower placed in a sphere emits 12.57 lumens or mean spherical candela equals to 12.57 lumens.
  • Light is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye (about 400–700 nm, or perhaps 380–750 nm). In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.
  • Lighting Quality is the sum total of all lighting quality features. For good lighting, a lighting installation needs to take account of every relevant quality feature and not be designed on the basis of just a single criterion such as illuminance.
  • Lumens Per Watt (LPW) A measure of the efficacy of a light source in terms of the light produced for the power consumed. For example, a 100-watt lamp producing 1750 lumens gives 17.5 lumens per watt.
  • Luminance is the term used to describe the specific light which comes off a surface whether off a filament, light bulb, lens, louver, tabletop, etc. Luminance varies with both the direction at which you view the surface and its gloss characteristics. Luminance is measure in candela per square foot.

[edit] M

  • Moonlight is the light that comes to Earth from the Moon. This light does not originate from the Moon, but actually originates from sunlight.
  • Metal Halide lamp a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercury vapor lamp, improved luminous efficacy and light color is obtained. Originally created in the late 1960s for industrial use, metal halide lamps are now available in numerous sizes and configurations for commercial and residential applications. Like most HID lamps, metal halide lamps operate under high pressure and temperature, and require special fixtures to operate safely.
  • Moonlight is the light that comes to Earth from the Moon. This light does not originate from the Moon, but actually originates from sunlight. The Moon does not, however, reflect sunlight like a mirror, but it emits light from those portions of its surface which the Sun's light strikes.

[edit] O

[edit] P

  • Polarization (also polarisation) is a property of certain types of waves that describes the orientation of their oscillations. Electromagnetic waves, such as light, and gravitational waves exhibit polarization; acoustic waves (sound waves) in a gas or liquid do not have polarization because the direction of vibration and direction of propagation are the same.

[edit] R

  • Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected.

[edit] S

  • Skyglow (or sky glow) is the wide-scale illumination of the night sky or parts of it. The most common cause of skyglow is artificial light that emits light pollution, which accumulates into a vast glow that can be seen from miles away and from high in the sky. Skyglow from artificial lights is common throughout the world and can be observed over most cities and towns as a glowing dome of the populated area.
  • Starlight refers to the visible radiation emitted by stars other than the Sun.
  • Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun.
  • Sunrise is the daily appearance of the sun on the eastern horizon as a result of the earth's rotation. In the United States, it is considered as that instant when the upper edge of the sun appears on the sea level horizon. In Great Britain, the center of the sun's disk is used instead. Time of sunrise is calculated for mean sea level.
  • Sunset The daily disappearance of the sun below the western horizon as a result of the earth's rotation. In the United States, it is considered as that instant when the upper edge of the sun just disappears below the sea level horizon. In Great Britain, the center of the sun's disk is used instead. Time of sunset is calculated for mean sea level. The time of sunset is defined in astronomy as the moment the trailing edge of the sun's disk disappears below the horizon in the west. Due to refraction of light in the atmosphere, the ray path of the setting sun is highly distorted near the horizon making the apparent astronomical sunset occur when the sun’s disk is already about one diameter below the horizon. Sunset should not be confused with dusk, which is the moment at which darkness falls, when the sun is about eighteen degrees below the horizon. The period between the astronomical sunset and dusk is called twilight.

[edit] T

  • Temperature The quantity measured by a thermometer. Bodies in thermal equilibrium with each other have the same temperature. In gaseous fluid dynamics, temperature represents molecular kinetic energy, which is then consistent with the equation of state and with definitions of pressure as the average force of molecular impacts and density as the total mass of molecules in a volume. For an ideal gas, temperature is the ratio of internal energy to the specific heat capacity at constant volume.

[edit] W

  • Watt W An electrical expression that represents Amps X VoltageNormally used in AC circuits to denote the total power required in a system. See also Amps, Voltage.
  • Wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats.

[edit] Also see

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