Terminology of LED Lighting
Ampere (Amp)
The standard unit of measurement for electric current that is equal to one coulomb per second. It defines the quantity of electrons moving past a given point in a circuit during a specific period. Current (Amps) = Power (Watts) / Voltage (Volts)
Average life
Unit: hours
Definition: The length of time during which >50% of the lamps reach the end of their individual lives.
Ballast
A device that limits and regulates the current going through a fluorescent or mercury lamp at the desired constant value while providing the nescessary starting voltage.
Candela (cd)
The luminous intensity as defined by the international metric standard (SI). The term, retained from the early days of lighting, defines a standard candle of a fixed size and composition as a basis for evaluating the intensity of other light sources.
CIE Chromaticity Diagram
A horseshoe shaped line connecting the chromaticities of the spectrum of colors
Color rendering index (CRI)
Unit: Ra
Definition: it is a measure of the ability of a light source to reproduce the colors of various objects being lit by the source. It is the calculated rendered color of an object. The higher the CRI (based upon a 0-100 scale), the more natural the colors appear. Natural outdoor light has a CRI of 100. Common lighting sources have a large range of CRI. A low CRI rating suggests that the colours of objects will appear unnatural under that particular light source.
Color spectrum
All wavelengths perceived by human sight, usually measured in nanometers (nm).
Color temperature
Unit: K (Kelvin)
Definition: Of a solid surface, that temperature of a blackbody from which the radiant energy has essentially the same spectral distribution as that from the surface.
- Color Temperature >5000k: the light color belongs to cool and cold one (white with a little blue), cold atmosphere.
- Color Temperature 3300-5000k: the light color ranks middle (white), refreshing atmosphere.
- Color Temperature <3300k: the light color belongs to warm one (red with white), steady-going atmosphere.
Cool white
A description of light with a correlated color temperature between 5000K and 7500K, usually perceived a slightly blue.
Correlated color temperature (CCT)
The phrase use to describe the temperature, at which a Planckian Black Body Radiator and an illumination source's appear to match, usually specified in Kelvin (K).
Diffuser
A translucent piece of glass or plastic sheet that shields the light source in a fixture. The light transmitted throughout the diffuser will be redirected and scattered reducing glare and improve uniformity.
Driver
Electronics used to power illumination sources.
Economic life
Unit: hours
Definition: the hours of operation a lamp is designed to provide in terms of optimum light output, aesthetic quality, and economic energy consumption. The "economic life" of lamps is generally defined as 60% of the lamp’s rated life. For example, outdoor lighting bulbs are designed as 70 percent to the rated life, and indoor lighting bulbs are 80%.
Efficacy
(Luminous 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).
Flicker
Variation in light intensity due to 50 Hz operation. Can cause eye strain and fatigue due to stroboscopic effects.
Flux
The sum of all the lumens (lm) emitted by a source (see lumen).
Glare
Direct glare is caused by light coming directly to the eye from a light source. Indirect glare is light reflected from a surface in the direction of the eye. Both can harm vision and cause visual discomfort, annoyance or loss of visual performance.
Illuminance
Symbol: E
Unit: lux (Lm/m2)
Definition: the unit of luminance in the International System of Units (SI). It is defined in terms of lumens per meter squared (lm/m 2)
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.
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. A 60-Watt Soft White incandescent lamp provides 840 lumens.
Luminaire
A lighting fixture complete with installed lamps and other accessories.
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). One lux equals 0.093 footcandles.
Luminance
Symbol: L
Units: cd/m2
Definition: Luminous intensity per unit projected area of any surface, as measured from a specific direction.
Luminous efficiency
Unit: Lm / w
Definition: The ratio of the total emitted luminous flux, in lumens, to the total electric power consumption in watts.
Luminous flux
Symbol: Φ
Unit: lumen (Lm)
Definition: The rate of flow of light per unit of time, especially the flux of visible light expressed in lumens.
Luminous flux in lumens = Radiant power (watts) x 683 lumens/watt x luminous efficacy
Luminous intensity
Symbol: I
Unit: Candela (cd)
Definition: The luminous flux density per solid angle as measured in a given direction relative to the emitting source.
Mercury vapor lamp
A type of hight intensity discharge (HID) lamp that uses mercury in an excited state to produce light, most of which is produced by radiation from mercury vapour.
Metal halide lamp
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.
MR16
A low voltage reflector lamp which directs a sharp, well-defined beam of light. Typically the lamp and reflector are one unit.
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.
RGB color
Stands for "Red Green Blue." It refers to the three hues of light, that can mix together to form any color. From the image above, blue and green combine to produce turquoise, green and red combine to produce yellow, red and blue combine to make violet. When the highest intensity of red, green and blue is mixed together, white light is created. When each hue is set to zero intensity, the result is black. RGB LED lights allow you to control the lights to cycle through a continuous color changing pattern, or stop the controller at any color you like.
Volt
The term used to describe the electrical potential difference between oppositely charged conductors. It defines the force or pressure of electricity. For example there is a 1.5V potential between the top and bottom of a battery.
Voltage
The difference in electrical charge between two points in an electrical circuit is expressed in volts.
Warm white
A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.
Watt
Refer to the unit of electrical power used by an electrical device during its operation. It defines the rate of energy consumption by an electrical device when it's in operation. The energy cost of operating an electrical device is calculated as its wattage times by the hours of use. Many lamps come with rating in watts to indicate their power consumption. A light source with a higher lumen per watt value is more efficient.