LED LIGHTING FAQ's

Case Temperature

The temperature measured at the LED package or case.

Chromaticity

An objective specification of the quality of a color, independent of its luminance, and as determined by its or saturation and hue.

Color Definition

The color of uniformly illuminated objects described using three terms:

Hue: Describes the situation when the appearance of different colors is similar (e.g. matching blues and pinks).

Lightness: Describes a range of grayness between black and white.

Chroma: Describes the degree of departure from gray of the same lightness and increasing color (e.g. red, redder, pure red).

Color Gamut

The range of colors within the CIE Chromaticity Diagram included when combining different sources.

 

Color Model

An abstract mathematical model describing the way colors can be represented as groups of values or color components. RGB (Red-Green-Blue) is a color model with three color components, and CMYK (Cyan-Magenta-Yellow and Key (Black)) is a color model with four color components.

Color Rendering Index (CRI)

A measure of the degree of color shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable color temperature. The reference source has a CRI of 100.

Color temperature

The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent color, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.

Controller

A device that controls the output of color-changing and tunable white lighting fixtures. Controllers typically have software components for configuring fixtures and designing and editing light shows, and hardware components for sending control data to fixtures.

Correlated Color Temperature (CCT)

The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. Usually specified in Kelvin (K). The lower the Kelvin temperature, the warmer the light feels, or appears.

Delivered Light

The amount of light a lighting fixture or lighting installation delivers to a target area or task surface, measured in footcandles (fc) or lux (lx).

Direct-View Lighting Fixtures

Lighting fixtures intended for viewing, rather than for illumination. For example, arrays of direct-view fixtures or nodes are used in large-scale video displays, traffic signals, and signage applications.

Driver

All LED fixtures include an LED driver or power supply. This driver can be integral to the fixture, separate from the fixture or remotely located. Typically, the driver is an important part of every LED system and you should remember it is a factor when using LED fixtures.

Efficacy

The light output of a light source divided by the total electrical power input to that source, expressed in lumens per watt (lm/W).

Eye-sensitivity Curve

A bell-shaped curve describing the sensitivity of a human eye with normal vision to the spectrum of visible light. Also known as the eye-sensitivity curve. See spectral luminous efficiency function.

Flux / Luminous Flux

Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light

Forward voltage

LEDs are current driven devices. If an external current is passed through the device, a forward voltage will be developed across the diode.

Ghosting

An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.

Heat Sink

A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.

 

HID

High Intensity Discharge, usually referred to bulbs that use compressed gass and when voltage is applied creates a high intensity discharge or voltaic arch like in a lighting bolt and thus emmit light.

 

High Power LED

A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.

 

High-brightness

High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.

 

Hot / Cold Factor

The relative light output performance at a temperature compared to the light output at a nominal or test temperature. For LUXEON products this is the relative light output at 100C Tj compared to 25C Tj. For “Hot Tested” products like LUXEON A it is the relative light output at 100C Tj compared to 85C Tj.

Hot Testing

LED performance testing and specification at an elevated temperature of 85°C.

Illuminance

The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).

Illuminating Engineering Society of North America (IES)

The recognized technical authority on illumination, communicating information on all aspects of good lighting practice to its members, to the lighting community, and to consumers through a variety of programs, publications, and services.

Inboard Power Integration

An approach to power management that integrates the power supply directly into a fixture’s circuitry, creating an efficient power stage that consolidates line voltage conversion and LED current regulation.

Infrared (Near)

Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.

Junction Temperature

Junction temperature, noted as Tj, is the temperature of the LED’s active region.

Kelvin Temperature

Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.

Kelvin Temperature

Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.

LED Chip (Chip)

The light producing semiconductor device that may or may not be incorporated into an LED.

 

LED Driver

An electronic circuit that converts input power into a current source — a source in which current remains constant despite fluctuations in voltage. An LED driver protects LEDs from normal voltage fluctuations, overvoltages, and voltage spikes.

 

LED Light Engine

An integrated assembly comprised of LEDs or LED arrays, LED driver, and other optical, thermal, mechanical, and electrical components.

 

LED Luminaire

A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribut light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit.

 

Light Emitting Diode (LED)

A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

 

L70

L70 describes the brightness of an LED after a number of hours – often 50,000. If a product claims L70 after 50,000 hours, it means that after 50,000 hours of burning (nearly six years if the lights are on 24/7) the lights are now 70% as bright as they were when they were first installed. L70 doesn’t mean anything without the corresponding number of hours. You may also see terms such as L70 at 6,000 hours. Sometimes manufacturers will list L80 (or even L90) at 50,000 hours. This simply means that after 50,000 hours, the LEDs will be 80% (or 90%) as bright as they were initially. Be careful not to confuse L70 with LM79 or LM80.

LM79

This IES document applies to LED fixtures (but not to components.) It prescribes the approved method for “Electrical and Photometric Measurements of Solid-State Lighting Products.” In the beginning, LED products were the wild, wild west. Manufacturers claimed just about anything based on their own personal “test procedures.” LM79 gave structure to the chaos and today LM79 compliance can help ensure that you are comparing apples to apples when you read LED product literature.

LM80

This IES (Illuminating Engineering Society of North America)document describes the approved method for “Measuring Lumen Maintenance of LED Light Sources.” It applies to bare LED light sources and does not cover complete luminaires (fixtures.) The main story here is usable life. LED sources, like the old metal halide lamps, tend to fade over life instead of “burning out.” Again, when manufacturers are using the same test methodology, you can be comfortable when comparing products.

 

 

Lumen (lm)

The international (SI) unit of luminous flux or quantity of light and equals the amount of light that is spread over a square foot of surface by one candle power when all parts of the surface are exactly one foot from the light source. For example, a dinner candle provides about 12 lumens

 

Lumen Depreciation

Describes the percentage of light lost relative to the initial lumen output. See lumen maintenance for more information.

 

Lumen Maintenance

The luminous flux at a give time in the life of the LED. This is expressed as a percentage of the intial luminous flux.

 

Lumen Maintenance Curve

A graph illustrating the predicted average light output behavior over time of a single LED or solution.

 

Lumen Output

The total lumens emitted of a light source, system, or solution.

 

Luminaire

A lighting fixture complete with installed lamps and other accessories.

 

Luminous Efficiency

The percentage of total lamp lumens that a lighting fixture, luminaire, or system emits, minus any blocked or wasted light.

 

Luminous Flux

Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light

 

Lux (lx)

The SI (International) unit of illuminance, or luminous flux incident on a unit area, frequently defined as one lumen per square meter (lm/m2).

MacAdam Ellipse

A MacAdam ellipse is the region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse.

 

MCPCB

A widely accepted Printed Circuit Board (PCB) material with a Metal Core (MC) for better thermal performance, where LED chips are mounted.

Nits

Measurement of display screen brightness. 1 nit = 1 cd/m2.

 

NTSC Color Space

The range of colors within the CIE Chromaticity Diagram included when combining phosphor based RGB sources in CRTs such a televisions and computer monitors.

Onboard Power Integration

An approach to power management that integrates the power supply into a fixture’s housing, eliminating the need for an external power supply.

 

Organic Light-emitting Diodes (OLED)

Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, color, efficiency, cost, and lifetime.

Power Factor

The active power divided by the apparent power (i.e., product of the rms input voltage and rms input current of a driver).

 

Power Factor Correction

In an electronic device, such as an LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.

 

Pulse Width Modulation (PWM)

A method, used by LED drivers, to regulate the amount of energy to the LEDs. PWM turns LEDs on and off at high frequency, reducing total ON time to achieve a desired dimming level.

Radiant Flux

The total energy emitted by a light source across all wavelengths, measured in watts.

 

Radiometry

The measurement of radiant energy (including light) in terms of absolute power. Compare photometry.

 

RGB Color Model

An additive color model in which red, green, and blue light are added together in different proportions to produce a broad range of colors, including white.

 

RGB White

A method of producing white light by combining the output from red, green, and blue LEDs.

Solid-state lighting

A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.

 

Spectral Luminous Efficiency Function

A bell-shaped curve describing the sensitivity of a human eye with normal vision to the spectrum of visible light. Also known as the eye-sensitivity curve.

 

Steradian

The standard unit of solid angle. Describes two-dimensional angular spans in three-dimensional space.

 

Subtractive Color Model

A color model that applies to reflective surfaces such as paints, dyes, and inks. Combining red, green, and blue in equal amounts produces black.

Tc

Case Temperature

 

Thermal management

Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.

 

Thermal Pad Temperature

The measured temperature of the thermal pad during tesing. The thermal pad aides in the conduction of heat away from the component being cooled and into the heatsink. For more information refer to LUXEON® Rebel and LUXEON® Rebel ES Assemby and Handling Guide application brief 32.

 

Thermal Resistance (K/W)

The property of a material's ability to conduct heat.

 

Tj

Junction Temperature

 

Tp

Thermal Pad Temperature

 

Tunable White Light

White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of color temperatures.

Ultraviolet (UV)

Electromagnetic radiation with wavelength shorter than that of visible light.

Useful Life

The amount of light a lighting fixture delivers in an application, minus any wasted light.

Volt

The term used to describe the electrical potential difference between oppositely charged conductors, for example there is a 1.5V potential between the top and bottom of an AAA battery.

Wall Plug Efficiency

This typically refers to the effectiveness of converting electrical power to light output. It is defined as the ratio of the radiant flux to the input electrical power.

Warm White

A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.

Watt

The unit of electrical power as used by an electrical device during its operation. Many lamps come with rating in watts to indicate their power consumption.

 

White Point

The Coordinated Color Temperature (CCT) defined by a line perpendicular to the Planckian Black Body Curve and intersecting the measured chromaticity.