Whether you’re a lighting distributor or an energy contractor, it’s always helpful to have a common frame of reference when speaking with clients. That’s why we’ve pulled together this list of LED lighting industry terminology.
The unit for measuring rate of flow of electrical current in the International System of Units (SI): Current (Amps) = Power (Watts)/Voltage (Volts).
The quality or state of radiating more or less light. Because brightness is a perception, it can change depending on whether the object in question is seen against a light or dark background.
The SI unit of luminous intensity.
A raised overhead platform that gives energy contractors access to service areas and is used for mounting and accessing luminaires.
The quality of a color with regard to its purity and dominant wavelength, regardless of its luminance.
CLASS 0 LUMINAIRE
A luminaire with only basic insulation to protect against electric shock.
CLASS I LUMINAIRE
A luminaire with basic insulation, but that also typically features a way to connect accessible conductive parts to the protective conductor in a way that they cannot become live if the basic insulation fails.
CLASS II LUMINAIRE
A luminaire that relies on additional safety features — like reinforced insulation or double insulation — to protect against electric shock.
CLASS III LUMINAIRE
These luminaires rely on supply at safety extra-low voltage (SELV); voltages higher than that are simply not generated.
COEFFICIENT OF VARIATION (CV)
CV is used to measure the uniformity in lighting and is essentially the standard deviation of a set of illuminance values on a grid, divided by the average.
COLOR RENDERING or COLOR RENDERING INDEX (CRI)
A quantitative measure of the ability of a light source to reproduce surface colors accurately. CRI is rated on a scale from 1 to 100, with 100 meaning the most accurate representation of true color.
A device with speciality hardware and software that sends data to fixtures, allowing lights to be configured, controlled, and coordinated.
CORRELATED COLOR TEMPERATURE (CCT)
CCT, or Correlated Color Temperature is measured in degrees Kelvin, and indicates how “warm” or “cool” the light appears. A warm light would be about 2700K, while a cool light would be 5000K or more. (Looking for neutral light? Aim for 4000K.)
Daylight harvesting involves using the natural daylight in a space to offset the amount of lighting (and energy consumption) needed, using sensors and controls to dim and switch lights as the daylight in the space changes.
DID YOU KNOW?
Almost all Litetronics products are either capable of daylight harvesting right out of the box, or compatible with an optional made-to-order PIR sensor that enables occupancy sensing and daylight harvesting.
The amount of useful light a luminaire actually delivers to a given area (as opposed to the light produced in a lab setting). It is measured in foot-candles (fc) or lux.
DIGITAL MULTIPLEX (DMX)
Digital Multiplex, or DMX, is a one-way lighting protocol for controlling dimming and color mixing.
An electronic circuit device that controls and regulates current flow, providing a constant amount of power to the variable needs of LEDs.
The efficiency of a light source, or how well the light source produces visible light for the energy put into it. Measured in lumens/watt.
ELECTROMAGNETIC INTERFERENCE (EMI)
A disturbance caused by electromagnetic noise or interference from an external source that affects an electrical circuit. EMI (also known as radio frequency interference or RFI) can interrupt, obstruct, or otherwise limit the performance of the circuit.
Lighting engineered and intended for use in event of main lighting failure. While speciality emergency lighting is a popular option, other projects benefit from an emergency battery backup for LED fixtures, retrofits, and high bays.
EXTRA-LOW VOLTAGE (ELV)
Extra-low voltage, or ELV, is an electricity supply voltage in a range used in areas of increased risk, such as where water is often present. ELV means voltage of 50 V AC or 120 V DC.
A visible and repeated change in emitted light. Research shows flicker can contribute to headaches, eyestrain, and fatigue, and it can exacerbate migraines or photosensitive epilepsy.
A unit of illumination measured using a light meter. The unit is the light that falls onto the inside surface of a one-foot-radius sphere that has one candela at its precise center.
An effect that occurs when a lighting fixture continues to faintly glow after being turned off, due to residual voltage in the circuit.
Light that causes discomfort or reduces the ability to see. This is often caused by an excessive change of luminance, or a light source that is too bright compared with its background.
International Engineering Society of North America. The IESNA is a not-for-profit organization of the lighting industry and is the recognized technical and educational authority on illumination.
Indirect lighting, also called reflected or diffused light, is created by using fixtures to reflect light off surfaces such as walls, mirrors, and ceilings to distribute illuminance throughout the room while minimizing shadows and glare.
INITIAL LIGHT LEVELS
The average light levels when the luminaires are new — just after it has stabilized but before it has started to degrade or depreciate.
INGRESS PROTECTION (IP) RATINGS
The ingress protection (or IP) code indicates how well a device protects against solids (including dust) and liquids. The higher the number, the better the protection. A rating of IP01, for instance, would mean no protection from solids, but protection from condensation, while an IP68 would be protected totally from dust, as well as from long-term immersion in water, up to a specified pressure. (Our hazardous location LED high bay fixture has an IP66 rating.)
Kelvin (°K) is the SI base unit of measurement for temperature and is often used to measure the color temperature of a light source. (See also: Color temperature)
This refers to the lifetime measurement criteria used to describe an LED’s expected light output over its stated life span, and it predicts how many hours of use before the fixture degrades to 70% of its initial lumen output. The higher this number, the longer the fixture is expected to remain operational.
LED stands for light-emitting diode, which is a semiconductor device that emits light when a current passes through it, and it’s used not only in LED lighting, but also in electronic displays, digital watches and devices, and more.
An LED array is an assembly of LED packages (components) or dies (chips) on a circuit board or substrate. It can include optical elements, along with additional interfaces (like mechanical, electrical, or thermal) intended to connect to the load side of an LED driver.
The semiconductor device that emits like when a current flows through it.
An electronic circuit that inputs and regulates power into an LED or LED array. An LED driver protects sensitive LED components from voltage fluctuations.
A complete lighting unit consisting of LED-based elements, driver, and all other needed components. Luminaires are designed to be connected directly to a branch circuit.
LIGHT OUTPUT RATIO (LOR)
The light output ratio, or LOR, is the percentage of light that makes it out of the luminaire and is one measure of the efficiency of the fixture.
LIGHT LOSS FACTOR (LLF)
Also known as maintenance factor (MF), light loss factor is the ratio of the illuminance at a certain point in time, compared to when the light was newly installed. It factors in light loss caused by things like environmental factors and maintenance procedures.
A form of light pollution caused by unwanted light spilling onto another property.
LM70 is a measurement developed by IESNA (Illuminating Engineering Society of North America) to evaluate the useful lifetime of an LED luminaire, and it essentially lays out the expected number of operating hours until the light output has diminished to 70% of its initial levels.
LM80 was developed by IESNA (Illuminating Engineering Society of North America) to evaluate LED lighting performance over time. The LM80 standard also requires lumen maintenance data for at least 6,000 hours of constant DC mode operation, as well as testing at 55°C and 85°C. Lighting manufacturers use the LM-80 test results as part of their submissions to the ENERGY STAR program.
A unit of luminous flux, used to measure the overall visible light output. The higher the number, the more light that’s emitted.
A reduction in the lumens emitted from the light source, shown in graph form with the percentage reduction in hours. (See also: Light loss factor)
LUMEN EFFICIENCY (lm/W)
Lumen efficiency or luminous efficiency (lm/W) is the ratio of the lumens emitted by a luminaire or system, to any blocked or wasted light.
The luminous flux at any given point during the lifetime of an LED, expressed as a percentage of the LED’s initial luminous flux.
LUMEN MAINTENANCE CURVE
A graph illustrating the anticipated average light output over time of a single LED or light source typically showing the percentage of initial lumens deteriorating over the light source’s lifespan.
Quantifies the brightness of a surface. Expressed as cd/m2, luminance measures the intensity of light emitted from a surface at a particular angle of view, thus being an indicator of how bright the surface will appear.
Measured in lumens, it is the total light emitted by a lamp.
The SI unit of illuminance. It is equal to one lumen per square meter.
A plotted range on the CIE chromaticity diagram that depicts human color tolerance. Any point within the ellipse is indistinguishable (to the human eye) from the color at the center of the ellipse. It is only at the boundaries of each ellipse when a noticeable difference in chromaticity is evident.
The value, in foot-candles or equivalent, below which the light level is not supposed to fall.
MAX TO MIN UNIFORMITY RATIO
The ratio of maximum to minimum illumination levels, meant to measure uniformity of light. A max/min uniformity ratio of 2:1 means that the brightest point is no more than double any other point. 10:1 is a commonly used uniformity ratio.
NEMA is a system of classifying light distribution, primarily with flood lights. It describes the light distribution as “beam spread.” The NEMA beam spread indicates the two edges where the light intensity is 10% of the maximum beam intensity.
OBTRUSIVE LIGHT OR SPILL LIGHT
Uncontrolled light that spreads beyond the boundary of the property where the lighting is operating.
The branch of science covering the measurement of light, in terms of its perceived brightness to the human eye.
POWER FACTOR (PF)
The ratio of active power to apparent power, measuring how efficiently electrical power is being used. Power factors can range from 0 to 1.0: The higher the power factor, the more efficient.
POWER FACTOR CORRECTION
A process to increase the power factor of a load toward the ideal of 1.0. It typically involves a system of inductors, capacitors, or voltage converters.
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 a high frequency (faster than can be seen by the human eye) to reduce the average light output and create a dimming effect.
RATED MEDIAN USEFUL LIFE
Also known as Average Rated Life (ARL), this is measured by how long it takes for half the light bulbs in a test batch to fail. Most LEDs have an ARL of 50,000.
RGB COLOR MODEL
An additive color model in which red, green, and blue light are added together in different ways and proportions to produce a broad range of colors, including white.
A type of lighting in which semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) are used as sources of illumination instead of electrical filaments, plasma, or gas.
The design, tools, and technologies used to control the operating temperature range of a system. Examples include heat sinks and improved air flow.
A material’s resistance to heat flow.
TUNABLE COLOR TEMPERATURE
LED fixtures that combine channels of RGB color and cool white LEDs, allowing for a range of color temperatures, letting users adjust the color temperature of a lamp without having to change out the bulb.
UNIFORMITY GRADIENT (UG)
Rate of change of illuminance between adjacent (grid) values, measuring how fast the values fall off between points. Typically used to measure uniformity in cases like sports lighting.
Either the ratio of the illuminance in the brightest-lit spots to that in the dimmest areas (max/min), or of the average illuminance of the whole area to that of the dimmest spots (avg/min). Either the ratio of maximum to minimum illumination levels, or average to minimum illumination levels, meant to measure uniformity of light. (See also: Max to min uniformity ratio.)
The number of operating hours before a light source is expected to reach a certain percentage of its initial lumen output. Also known as lumen maintenance thresholds. (See also: L70 hours.)
VERTICAL AIMING ANGLES
The angle formed between the horizontal and a line through the center of the vertical beam spread. It measures the degrees below horizontal that light fixtures are aimed at the field.
This is the quantity of light on a vertical plane, like a wall.
The SI unit of potential difference and electromotive force.
The SI unit of power or radiant flux.