Lumens, candela, and nits are the three units often used to describe the brightness of LED displays and other display products. When introducing the brightness parameters of LED display screens, they are generally expressed by Nit (sometimes called Nits), and some manufacturers mark them as CD / m2 (1 NIT = 1 CD / m2). In the field of projectors, such as DLP and engineering projection, it is more used to measure the brightness of the projector in lumens. Then the question is coming, which also means brightness. Why do nits for LED displays and lumens for DLP?
First, understand the brightness and its unit nits
Luminance (luminance) is the physical quantity that the human actually feels about the intensity of the luminous or reflected light on the surface of the luminous body or the irradiated object. The two quantities of brightness and light intensity are often confused and used in ordinary daily language. The International System of Units stipulates that the sign of brightness is L and the unit is nit.
Nit (Nit) is an international unit of measure unit for measuring brightness. Nit nit = candela per square meter (cd / m2). Among them, Candela is the main unit of the International System of Units for measuring luminous intensity, and square meters is the derived unit of the International System of Units for measuring the area. Nit, derived from the Latin "nitere", means irradiation.
Then, understand the light intensity and its unit Candela
Luminous intensity is the luminous flux emitted by a light source within a unit solid angle in a given direction. It is used to represent the physical quantity of the light source's luminous intensity. The international unit is candela, also known as candlelight, and the symbol is cd. Compared with the unit for measuring energy intensity, the definition of luminous intensity takes into account human visual factors and optical characteristics, and is established on the basis of human vision.
The unit of luminous intensity was originally defined by candles. The luminous intensity of an ordinary candle is about 1 candela (cd).
Let's understand the luminous flux and its unit lumens
The sum of the energy emitted by the light source and received by the human eye is the luminous flux.
Lumen (lm) is a unit of derivation of the International System of Units of Luminous Flux, which is a measure of visible light emitted from a light source.
With the above knowledge as a reserve, we can think about the difference between lumens, candela, and nits and their usage through the following two questions.
It also means brightness. Why do LED displays use nits and projectors use lumens?
In the brightness of the luminous body, generally the active luminous body uses the luminous intensity unit CD, such as LED; the passive or luminous objects such as reflective or transmissive type use the luminous flux unit lm, such as the projector. The LED display screen arranges the point light source array together, and cd / m2, which is nit, indicates that the brightness is more appropriate.
To put it simply, in display devices, nit is used for active display and lumens is used for passive display. It can also be understood that display devices (LED display screens, liquid crystals) that use planar light sources generally use nit (cd / m?), And display devices (projectors) that use point light sources use lumens to indicate brightness, which can obviously reflect point installation. The light source will have the characteristics of gradual brightness from the middle to the surroundings on the projection surface.
Why does the brightness of LED lights pay attention to lumens, and the brightness of LED displays pays attention to nits?
Lumens are often used to mark products such as light bulbs, flashlights, etc., which is a gradual value, and the brightness gradually decreases from the center to the outside. NIT mainly labels products such as monitors and other uniform display devices. In theory, the products that reach the display level should use the latter, which is the unit of NIT.
Finally, the conversion relationship between the three:
cd = lm / sr
nit = cd / m2,
nit = lm * m2 / sr
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