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LED is an acronym for Light Emitting Diode. It is an electroluminescence semiconductor device. While electricity flow through
the LED, electrons(-) recombine with holes(+) at the junction of two doped semiconductors, which causes emitting a photon
whose energy is determined by the band gap of the material used.
Luminous flux: It is a measure of the power of light in the visible spectrum. In other words, it describes the quantity of the output
light, visible to humans, from a light source and its unit is the lumen. In the case of a lighting fixture, it is used for the output light
from the luminaire after optical losses. For luminaires with traditional light sources, generally the electrical power is used, for
instance, 4x14W; however, with LED luminaires it is best to use luminous flux to describe a luminaire.
Efficacy: Efficacy of a light source is its capacity to produce light. Electrical light sources convert electrical power into heat and
light. The ratio of the heat and light determine how efficient a light source is. In short, it is luminous flux divided by consumed
power. The efficacy of LEDs used in luminaires is minimum 100 lumens per 1 Watt and for mid-power class LEDs this value
increases up to 180lm/W.
Illuminance: It is used to describe how much a surface is lit. Illuminance is found by dividing total luminous flux incident on
the surface by its area and its unit is lux. The required illuminance levels for various places is shown on pg(195) according to EN
CRI (Color Rendering Index): Color rendering index of a light source shows its quality to reveal true colors of the objects
compared to the natural light source. White light is composed of several colors and their mixing ratios determine the CRI value.
It ranges from 0 to 100 and there are 15 different wavelengths chosen to calculate CRI. For interior lighting, minimum 80 is
recommended. As long as optics used in luminaire is high-quality, the CRI value of a luminaire is determined by only the light
CCT (Correlated Color Temperature): The color of a white light source defines its color temperature. On color space, white
light is defined not a singular point but rather in a region. In this region, white light shifts from yellowish white to bluish white.
CCT is defined by using a black body which emits light when it is heated. What is special about the black body is that it emits through
all of the spectrum, which consequently means that it can emit perfect white light. Therefore, when white light is described as
4000K, it means that if we heat the black body to 3727°C, item its the white light with the same color.
During the manufacturing process of LEDs, fluorescence material coating is used to convert blue light to white light. Due to this
stage’s complications, LEDs are made in various colors centered on targeted color temperature. Therefore, manufacturers
simply classify LEDs into different groups which are defined by ANSI (American National Standards Institute) binning. Below
is the binning diagram on color space.