COLOR RENDERING INDEX (CRI): A CIE scale used to indicate the color rendering accuracy of a light source compared to a reference source of the same color temperature, and is the average for eight standard colors, Ra8. Expressed on a scale of 1 to 100, a value of 100 indicates no distortion. A low CRI rating indicates that the colors of objects will appear distorted under that particular light source.
COLOR TEMPERATURE: Color temperature in Kelvin (K) is a term to describe the color appearance of a light source, related to the color of a black body radiator. If the color point for the source does not lie on the black body locus, its color temperature is given by the temperature of the black body which it most closely matches, and is its correlated temperature. The measurement can also be described as the "warmth" or "coolness" of a light source. Generally, sources below 3200K are considered "warm;" while those above 4000K are considered "cool" sources.
COMPACT FLUORESCENT LAMP (CFL): A small fluorescent lamp that is often used as an alternative to incandescent GLS lamps. The lamp life is 4 to 10 times longer than incandescent lamps, and is some 3-5 times more efficient; known generally as CFL lamps, and available in many versions. All require a ballast, which may be integral with the lamp.
EFFICACY: A metric used to compare light output to energy consumption. Efficacy is measured in lumens per watt. Efficacy is similar to efficiency, but is expressed in dissimilar units. For example, if a 100-watt source produces 9000 lumens, then the efficacy is 90 lumens per watt.
FLUORESCENT LAMP: Is a tubular lamp filled with mercury vapor at a low-pressure, and a small amount of an inert gas such as argon or krypton to aid starting and arc regulation. Electrodes are sealed into each end, and the light produced by the discharge is predominantly in the ultra-violet region. The inside of the tube is coated with fluorescent powders or phosphors, which the ultraviolet light excites to produce visible light. A wide range of colors and efficacies is available using different phosphors, individually or in combination.
HALOPHOSPHATE: Phosphors based on calcium halophosphate, used for fluorescent tubes and mercury fluorescent lamps. They provide the common fluorescent lamp generic colors such as White, Warm White, and Daylight. Halophosphate lamps are relatively cheap, have good efficacies, and reasonable lumen maintenance characteristics.
HID: Abbreviation for high intensity discharge. Generic term describing mercury vapour, metal halide, high pressure sodium, and (informally) low pressure sodium light sources and luminaires.
ILLUMINANCE: A photometric term that quantifies light incident on a surface, usually the working plane. Illuminance is commonly called light level. It is expressed as lumens per square meter (lux).
LOW-PRESSURE SODIUM: A low-pressure tubular discharge lamp in which light at 589nm is produced by radiation from sodium vapor. A largely monochromatic light source, so color rendition is very poor (most colors are rendered as grey). This lamp type has very high efficacies, and is mainly used in street lighting.
LOW-VOLTAGE LAMP: A lamp for use at lower than 120V supply, (typically 12V compact quartz halogen). These lamps require the use of a transformer, with adds a further watts loss to the circuit. Popular lamps are MR11, MR16. Infra-red reflecting versions offer lower lamp wattages.
LUMEN: Unit of light output, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp, notionally measured at 100hr.
LUMINAIRE: A complete lighting unit consisting of a lamp or lamps, lampholders, optical elements to distribute the light, and the means for connection to a power source. Control gear, if required, may be integrated within the luminaire.
LUMINAIRE EFFICIENCY: The ratio of total lumen output of a luminaire and the lumen output of the lamps, expressed as a percentage. For example, if two luminaires use the same lamps, more light will be emitted from the fixture with the higher efficiency.
LUX (lx): The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square metre.
MAINTAINED ILLUMINANCE: The average illuminance over the reference area at the end of the complete maintenance cycle, and is the minimum value to which the illuminance is allowed to fall.
MERCURY VAPOUR LAMP: A high intensity discharge (HID) lamp with a mercury filled arc tube producing UV light which excites the phosphor coating of the outer bulb and provides moderate efficacy and color rendering, and a long lifetime.
METAL HALIDE: A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. This lamp is typically available in clear and phosphor-coated lamps and has a high CRI and efficacy.
OPTICS: A term referring to the light-controlling components of a luminaire (such as reflectors, refractors, lenses, and louvers).
PAR LAMP: (parabolic aluminized reflector) An incandescent or metal halide lamp with a pressed glass parabolic reflector, minimizing reflection losses behind the filament or arc tube. Lamps are available with flood or spot distributions.
PAR 36: A PAR lamp that is 36 one-eighths of an inch in diameter (102mm) with a parabolic shaped reflector.
QUARTZ HALOGEN LAMP: A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens (namely iodine, chlorine, bromine, and fluorine), which through a recycling process effectively slow the rate of evaporation of the tungsten filament. This lamp is also commonly called a tungsten halogen lamp and exhibits higher efficacies than similar wattage incandescent lamps. Some examples would be MR-16, MR-11, etc.
T12 LAMP: (USA) Industry term for a fluorescent lamp (tube) that is 12/8th of an inch or 38mm in diameter. Other sizes are T10, T8 and T5 lamps.
TRIPHOSPHOR: Fluorescent lamps with high efficacy use three rare earth phosphors to produce lamps that are referred to as tri-band or tri-phosphor lamps. There is some evidence to indicate that these lamps produce greater visual clarity at equal illuminance, and that equal visibility can be achieved at slightly lower light levels. These lamps generally have a higher color rendering index than halophosphate lamps. Triphosphor lamps are frequently designated by three digits to indicate their CRI and color temperature. They have excellent lumen maintenance characteristics.
WATT (W): The unit for measuring electrical power, 1 watt = 1 joule/sec. It defines the rate of energy consumption by an electrical device when it is in operation. The energy cost of operating an electrical device is calculated as its wattage times the hours of use. In single phase circuits, it is related to volts and amps by the formula: Volts x Amps x PF = Watts. (Note: For AC circuits, PF (power factor) must be included.) PF allows for variations of this metric due to capacitance or inductance combined with resistance and in effect is a vector quantity used to determine real power vs apparent power.