Light is a form of energy. The essence of light is an electromagnetic wave, which is a very small part of the entire electromagnetic spectrum.
Visible light: part of the radiant energy emitted by the light source, that is, the radiant energy that can produce vision. Often referred to as "visible light".
Wavelength of visible light: from 380nm----780nm
Ultraviolet wavelength: from 100nm---380nm, invisible to the naked eye.
Infrared wavelength: from 780nm---1mm, invisible to the naked eye.
Luminous flux (lm)
The calculation formula of the energy that the light source radiates to the surrounding space in a unit time and makes the human eye feel light: Φλ=683PλVλ
In the formula, Φλ—the luminous flux with a wavelength of λ, lumens (lm);
P λ—radiative flux with wavelength λ (the energy emitted by the radiation source in unit time, the unit is W);
Vλ—spectral light efficiency with wavelength λ;
683 — The maximum spectral light efficiency, for photopic vision, at λ=555nm, its value is 683lm/W.
If it is polychromatic light, its luminous flux is the sum of each monochromatic light, namely Φλn=Φλ1+Φλ2+…=KmΣ[PλVλ]
Light source efficiency (lm/W)
Indicates the number of lumens that the light source can emit per watt of power consumed, that is, the light effect.
Luminous efficiency is an important indicator to measure the luminous efficiency of a light source.
Luminous intensity (cd)
The luminous flux emitted by a light source within a unit solid angle in a certain direction in space.
Calculation formula: Iθ=Φ/ω
In the formula, Iθ—the light intensity of the light source in the direction of θ;
Φ - the luminous flux (lm) received by the sphere A;
ω - The solid angle (Sr) corresponding to the sphere, that is, the angle formed by the surface area S of the sphere to the center of the sphere, measured by the ratio of the surface area S to the square of the radius of the sphere, ω=A/r2.
The luminous flux received per unit area of the illuminated surface
Calculation formula: E=Φ／A
In the formula, E—the illuminance on the illuminated surface, lux (lx);
The luminous flux received on the Φ-A area (lm);
A—the area that receives the luminous flux;
When the diameter of the light source is less than 1/5 of the distance from the light source to the illuminated surface, the light source can be regarded as a point light source.
The luminous intensity of the luminous body per unit area in the line of sight direction
Calculation formula: Since the visual perception formed by the imaging of a luminous body on the retina is proportional to the illuminance of the object image on the retina, the greater the illuminance of the object image, the brighter we feel; The projected area of is inversely proportional to the luminous intensity of the luminous body in the direction of sight, so there are:
where Lą—the surface brightness of the luminous body along the ą direction (cd/m2);
Ią—the luminous intensity of the luminous body along the ą direction (cd);
Scosą — the projection surface of the illuminant in the direction of sight (m2);
Among all photometric quantities, brightness is the only quantity that directly causes the visual perception of the eye.
Color temperature (K)
A standard black body is heated, and as the temperature increases, the color of the black body begins to gradually change along dark red-light red-orange-yellow-white-blue, when the color of the light emitted by a light source is the same as the color of the standard black body at a certain temperature. At the same time, we call the absolute temperature of the black body at that time as the color temperature of the light source, which is represented by the absolute temperature K.
The degree to which the light source presents the color of the object itself is called color rendering, usually called "color rendering index" (Ra).
That is, the degree of color fidelity. The light source with high color rendering has better color performance, and the color we see is close to the natural primary color. The light source with low color rendering has poor color performance, and the color deviation we have seen. Also larger.
According to the International Commission on Illumination (CIE), the color rendering index of sunlight is Ra 100, and the color rendering index of various light sources varies.
There are objects with extremely high brightness in the field of view, or the brightness contrast is too large, or there is extreme contrast in space and time, which can cause uncomfortable vision, or cause visual function to decline, or produce both effects at the same time. phenomenon called glare.
Glare is the most important factor affecting lighting quality.
Four factors that affect glare
1: Lamp brightness
2: The length of the room and the height at which the lamps are installed (ie, the distance to height ratio)
3: Visual adaptation level represented by average horizontal illuminance
4: Types of lamps, such as whether the side of the lamps emits light, etc.
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