Light_Vocabulary

**Ballast** An auxiliary piece of equipment required to start and to properly control the flow of current to gas discharge light sources such as [|fluorescent] and [|high intensity discharge (HID)] lamps. Typically, magnetic ballasts (also called electromagnetic ballasts) contain copper windings on an iron core while electronic ballasts are smaller and more efficient and contain electronic components.

A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise.
 * Bayonet**

Metal filaments that emit electrons in a fluorescent lamp. Negatively charged free electrons emitted by the cathode are attracted to the positive electrode (anode), creating an electric current between the electrodes.
 * Cathode**

A switching device sensitive to current and heat that automatically disconnects ballast if the temperature exceeds UL temperature limitations.
 * Class P Thermal Protector**

The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 10% of maximum
 * Field Angle**

The periodic variation in light level caused by AC operation that can lead to strobe effects.
 * Flicker**

An integral multiple of the fundamental frequency (60 Hz) that becomes a component of the current.
 * Harmonic**


 * Circline**: a type of fluorescent lamp that is made up of a circular tube of glass; when placed in a light fixture the ballast that powers this type of lamp is usually located in the center of the circline lamp

Formula stating that if you double the distance from the light source, the light level goes down by a factor of 4, if you triple the distance, it goes down by a factor of 9, and so on.
 * Inverse Square Law**

A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.
 * Luminaire**

A high intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium. Some lamp types may also utilize phosphor coatings. GE trade names include: Multi-Vapor®, ConstantColor® CMH®, PulseArc®, Staybright®, Watt-Miser®, ChromaFit and Arcstream®.
 * Metal Halide Lamp**

Capacitor used in ballasts to help provide power factor correction. Contains no polychlorinated biphenyls and meets EPA requirements.
 * Non-PCB Capacitor**

Chemical pollutant formerly used in ballast capacitors that were part of ballasts. It is now illegal to use PCB's and most such ballasts have been replaced over time.
 * PCB (Polychlorinated Biphenyls)**

Vision where the rods of the retina are exclusively responsible for seeing, typically like the light levels in the countryside on a moonless, starlit night
 * Scotopic**

A measure of the distortion of the input current on alternating current (AC) power systems caused by higher order harmonics of the fundamental frequency (60Hz in North America). THD is expressed in percent and may refer to individual electrical loads (such as ballast) or a total electrical circuit or system in a building. ANSI C82.77 recommends THD not exceed 32% for individual commercial electronic ballasts, although some electrical utilities may require lower THDs on some systems. Excessive THDs on electrical systems can cause efficiency losses as well as overheating and deterioration of system componenets.
 * Total Harmonic Distortion (THD)**

High voltage surges through an electrical system caused by lightning strikes to nearby transformers, overhead lines or the ground. May also be caused by switching of motors or compressors, as well as by short circuits or utility system switching. Can lead to premature ballast failure.
 * Transients**


 * Neodymium**: a rare earth element discovered in 1885 with an atomic number of 60 in the Periodic Table of Elements. It is a fairly common silvery metal that is used to make slightly purple glass envelopes for incandescent light bulbs, eye protection goggles for welding and glass blowing, laser rods, filters to color correct light for art displays, and lenses used by astronomers to calibrate spectrometers, optical instruments used for analyzing light. Using this substance in an [|incandescent light bulb] makes it less "yellowish" and more like natural outdoor light; however, the use of these "daylight" light bulbs can "expose" the flaws or inconsistencies in things.


 * R Lamp**: an [|incandescent], cone-shaped, light bulb that has a reflecting surface on the inside rear of the glass envelope. Variations of this lamp type are the bulged reflector lamp (BR), the ellipsoidal reflector lamp (ER), and the small reflector lamp (R). Since mid-2008 BR and ER light bulbs greater than 65 watts, used mostly in commercial retail applications, have been outlawed from being manufactured. These banned light bulbs can be replaced with more-efficient halogen PAR light bulbs. Also since mid-2008, R20 light bulbs can be no more than 45 watts. If a higher wattage reflector-type lamp is needed, a more efficient halogen PAR20 light bulb can be used. The 65-watt BR30 light bulb, commonly used in homes and restaurants, may still be manufactured and sold.


 * Linear Spread Lens**: a lens designed to produce the asymmetrical distribution of light in one direction as opposed to a spread lens, which produces symmetrical distribution in all directions. This lens diverges light in one axis and leaves the other axis unchanged. A linear spread lens is sometimes called an elongated lens, elliptical lens, or a Skytex lens.