This section is a compilation of terms associated with lighting used frequently throughout this website. To make the explanation of some of the terms more complete, links are provided to the website of Lighting Research Center, New York. Getting a good grasp of these terms will help you to attain a good understanding of lighting basics and also in the better application of our products.

Lighting terminology powered by Lighting Research Center New York, USA

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
-- A --
Accent Lighting
Directional lighting to emphasize a particular object or draw attention to a display item.
Ambient Lighting
The general lighting present in an area - excluding task lighting and accent lighting but including general lighting and daylight.
-- B --
Ballast Factor
The fractional flux of a fluorescent lamp operated on a ballast compared to the flux when operated on the standard (reference) ballast specified for rating lamp lumens.
Ballasts
A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current and waveform) for starting and operating.
-- C --
Candela
The Standard International unit of luminous intensity. One candela is one lumen per steradian. Formerly, candle.
Candlepower
A curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
CCT
The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source.
CRI
Measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source, of comparable color temperature.
-- E --
Efficacy
The quotient of the total luminous flux emitted by the total lamp power input. It is expressed in lumens per watt (lm/W).
Efficiency
The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
-- G --
Glare
The sensation produced by luminances within the visual field that are sufficiently greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort, or loss in visual performance and visibility.
-- H --
Harmonic Distortion
Non-linear loads such as inductive or capacitive loads draw current in abrupt pulses rather than in smooth sinusoidal manner create harmonics. These pulses cause distorted wave shapes, due to which harmonic currents to flow back into other parts of the power system.

Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency e.g. if fundamental frequency is 50Hz, then the 2nd harmonic is 100Hz, the 3rd is 150Hz etc.

Harmonics are having adverse effects such as overloading of transformers (de-rating) and rotating equipment, tripping of circuit breakers and fuses, neutral overloading etc.
-- I --
Illuminance
The areal density of the luminous flux incident at a point on a surface.
-- L --
Lamp
A generic term for a source created to produce optical radiation. By extension, the term is also used to denote sources that radiate in regions of the spectrum adjacent to the visible.
Life
Average rated life (of a light source) is usually the number of hours when 50% of a large group of lamps have failed. For incandescent lamps, the number of hours per start does not significantly affect the average rated life. For discharge sources such as fluorescent and high intensity discharge, (HID) fewer hours per start (more switching) decrease lamp operating life; more hours per start increase it. The following operating hours per start are assumed in most published life ratings:
  • Fluorescent - 3 hours per start
  • HID - 11 hours per start
Light
Radiant energy that is capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum extends from about 380 to about 770 nanometers.
Lumen
Standard International (SI) unit of luminous flux. Radiometrically, it is determined from the radiant power. Photometrically, it is the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela.
Luminaire
A complete lighting unit consisting of a lamp or lamps and a ballast (when applicable) together with the parts designed to distribute the light, to position and protect the lamps, and to connect the lamps to the power supply.
Luminance
the quotient of the luminous flux at an element of the surface surrounding the point, and propagated in directions defined by an elementary cone containing the given direction, by the product of the solid angle of the cone and the area of the orthogonal projection of the element of the surface on a plane perpendicular to the given direction.
-- R --
Reactance
Reactance is a measure of opposition to a sinusoidal alternating current that arises from the presence of inductance and capacitance within a circuit.
Reflectance
The ratio of the reflected flux to the incident flux.
-- S --
SPD
A pictorial representation of the radiant power emitted by a light source at each wavelength or band of wavelengths in the visible region of the electromagnetic spectrum (360 to 770 nanometers).
-- T --
Total Harmonic Distortion
Total harmonic distortion is a measure of the harmonic distortion present in a signal expressed as the ratio of the sum of the powers of all harmonic components to the power of the Fundamental frequency.
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