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LED Lighting Definitions & Terms

Guide to LED Lighting Definitions Used on

Beam Angle: The angle, in degrees, between the two opposite directions in which the average intensity is 50% of the center beam intensity as measured in at least two rotational planes, 90° from each other, around and through the beam axis (ANSI C78.379-2006).

CFL: See Compact Fluorescent Lamp.

Color Rendering: Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant (CIE 17.4, ANSI/IES RP-16-10).

Color Rendering Index of a Light Source (CRI): The measured degree of color shift objects undergo when illuminated by a light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature (10CFR430.2).

Correlated Color Temperature of a Light Source (CCT): The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source (10CFR430.2).

Covered Lamp: A lamp with an integral ballast or driver and a translucent envelope over the light source(s). See Envelope.

Decorative Lamp: A lamp with a candle-like or globe shape envelope including shapes B, BA, C, CA, DC, G and F as defined in ANSI C79.1-2002.

Dimmable Lamp: A lamp that is capable of producing varying levels of light, for the purposes of this specification, the lamp must be capable of reducing light output to at least 20% when paired with a control or dimmer. 

Directional Lamp: A lamp having at least 80% light output with a solid angle of π sr, corresponding to a cone with an angle of 120°.(Commission of the European Communities (EC) No 244/2009). For purposes of this specification, ANSI standard R, BR and ER shapes are considered to be directional regardless of compliance with this definition.

Envelope: A transparent or translucent enclosure over a light source. An envelope can also consist of a reflector with integral front cover (adapted from ANSI C78.357-2010).

FTC: United States Federal Trade Commission.

Field Angle: The angle between the two directions for which the intensity is 10% of the maximum intensity as measured in a plane through the nominal beam centerline (ANSI/IES RP-16-10).

Flicker: Luminous flux modulation made perceptible by the motion of objects or by the motion of the observer’s eye when the observer’s eye is still.

GU24 Based Integrated Lamp: A lamp unit that integrates the lamp and its ballast. It does not include any replaceable or interchangeable parts, and utilizes the ANSI standardized GU24 base type.

IES: Illuminating Engineering Society.

Input Power: The power draw in watts of a ballast or driver and a light source system operating in a normal mode, as determined in accordance with 10 CFR 430.

Integrated LED Lamp: An integrated assembly comprised of LED packages (components) or LED arrays (modules), LED driver, ANSI standard base and other optical, thermal, mechanical and electrical components. The device is intended to connect directly to the branch circuit through a corresponding ANSI standard lamp-holder (socket). (ANSI/IES RP-16-10)

Lamp: A generic term for a man-made 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 (ANSI/IES RP-16-10).

LED Array or Module: An assembly of LED packages (components) or dies on a printed circuit board or substrate, possibly with optical elements and additional thermal, mechanical, and electrical interfaces that are intended to connect to the load side of a LED driver. Power source and ANSI standard base are not incorporated into the device. The device cannot be connected directly to the branch circuit (ANSI/IES RP-16-10).

LED Driver Case Temperature Measurement Point (TMPC): A location on an LED driver case, designated by its manufacturer, which will have the highest temperature of any point on the driver case during normal operation.

LED Package: An assembly of one or more LED dies that includes wire bond or other type of electrical connections, possibly with an optical element and thermal, mechanical, and electrical interfaces. Power source and ANSI standardized base are not incorporated into the device. The device cannot be connected directly to the branch circuit (ANSI/IES RP-16-10).

LED Temperature Measurement Point (TMPLED): A location on an LED package/module/array, designated by its manufacturer, which provides a surrogate temperature measurement location for the actual LED junction. The TMPLED may be a solder joint at the board attachment site, a point on the LED package case, or a location on the board of an LED module or array.

Light-emitting Diode (LED): A p-n junction solid-state device of which the radiated output, either in the infrared region, the visible region, or the ultraviolet region, is a function of the physical construction, material used, and exciting current of the device.

Lumen Maintenance: The luminous flux or lumen output at a given time in the life of the lamp and expressed as a percentage of the rated luminous flux or rated lumen output, respectively (10CFR430 Appendix W to Subpart B). Lumen maintenance is the converse of lumen depreciation.

Lumens per Watt (lm/W): The quotient of the total luminous flux emitted by the total light source power input. It is expressed in lm/W. (Adapted from ANSI/IES RP-16-10: ―Luminous Efficacy of a Source of Light‖)

MacAdam Color Ellipse: A space around a chromaticity coordinate that sets the boundary at which a given percentage of people areable to determine that two colors, one with chromaticity coordinates at the center of the ellipse, and one with chromaticity coordinates on the ellipse, are just noticeably different (adapted from IES Handbook 10 th Edition).

Multi-power Lamp: A lamp designed to produce multiple discrete light levels when inserted into a lamp socket controlled by a switching mechanism and is designated on the lamp packaging as being a multi-power lamp, e.g. 3-way lamp.

NEMA: National Electrical Manufacturers Association.

NRTL: Nationally Recognized Testing Laboratory as recognized by OSHA’s NRTL Program, which is a part of OSHA’s Directorate of Technical Support.

Omnidirectional Lamp: A general service replacement lamp with an ANSI standard base that emits the majority of light produced in an even distribution about the lamp with intensities in the 0-135° zone varying by no more than 20% from the average of all measured values, and having at least 5% of the total flux (lumens) emitted in the 135° to 180° zone. These lamps can be standard; having an ANSI standard lamp shape of A, BT, G, P, PS, S or T, or non-standard; a self-ballasted compact fluorescent that utilizes a bare spiral, or multiple (twin, triple, quadruple) tube arrangement.

OSHA: Occupational Safety & Health Administration.

Power Factor: The input power in watts divided by the product of RMS input voltage and RMS input current of a ballast or driver.

Rated Lumen Maintenance Life (LP): The elapsed operating time over which the LED light source will maintain the percentage, p, of its initial light output, e.g., L70 (hours): time to 70% lumen maintenance (IES LM-80-08).

Rated Wattage: The wattage marked on the lamp (10 CFR 430 Appendix W to Subpart B).

Referenced Incandescent Lamp: A traditional incandescent lamp that predates the federal efficiency standards in the 2007 Energy Independence and Security Act.

Run-up Time: The time between the application of power to the device and the time when the light output first reaches a specified percentage of stable light output, i.e., 80%, 90%, etc.

Secondary Optics: Materials modifying the distribution of light from, but not integral to a light source, including but not limited to lamp envelopes, reflectors, and total internal reflection optics.

Solid-State Lighting (SSL): The term ―solid-state‖ refers to the fact that the light is emitted from a solid object – a block of semiconductor – rather than from a vacuum or gas tube, as in the case of an incandescent and fluorescent lighting. There are two types of solid-state light emitters: inorganic light-emitting diodes (LEDs) or organic light-emitting diodes (OLEDs). (Sandia National Laboratories)

Standardized Color Ellipse: A MacAdam color ellipse defined by center chromaticity coordinates (CIE x, y) and a measure of certainty for detecting a color difference specified in standard deviation units called steps (ANSI C78.376-2001).

UL: Underwriters Laboratories

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