First, the electromagnetic theory of light
It is well known that light is an electromagnetic wave, which is composed of an electric field and magnetic field that alternately change. The theoretical proven, the human eye and the photosensitive instrument are the electric field strength E. For the intensity of light, it is generally described with average energy stream density, which is proportional to the square of the electric field strength amplitude A, namely:
Îα2
Generally we use three basic elements of the light source: color, purity and brightness.
Light has monochromatic light and complement light, and the color of light is determined by its frequency. If only a single frequency is included in a beam, it is monochromatic light (usually the spectral color red, orange, Yellow, green, blue, indigo, and purple are monochromatic light); A visible light containing all frequencies).
The purity is used to describe how much pure physical quantity of the color of the light, obviously monochromatic light is the pure, because it does not contain any other color, while white light is the least pure.
The brightness of light is a more complex concept, which contains many related concepts, and I will explain one by one.
1. Radial flux ξ: It represents a bunch of light through the radiation power of the unit area, and the unit is watt. For the relative radiation flux of light near a certain frequency λ, we are described with distribution functions e (λ). Thus, the light of a certain wavelength λ, its radiation flux can be expressed as:
ξ = e (λ) Dλ
2, the visual function ν (λ): The brightness of the radiation is still not sufficient to describe light, because the light of equal radiation flux is different due to frequency, and the visual intensity of human eye is different. The human eye is most sensitive to yellow-green light, and the infrared and ultraviolet rays are not visual. In order to characterize the objective radiation flux and the subjective feelings of the human eye, we introduced the concept of viewing function ν (λ). If there is a wave of light having a wavelength of λ and a wavelength of 555 nm, the radiant flux required for dark visually dispense is Δξλ and Δξ5555 nm, respectively, the ratio:
ν (λ) = Δξλ / Δξ555NM
It is called a visual function. The following figure is a visiting function curve by the experiment.
3, light flux ф: With a visual function, we can study the visual strength of the light source radiation to the human eye, that is, optical flux ф, which is equal to the product of radiation flux and the visiting function. Thus, the light of a wavelength λ, its light flux can be expressed as:
Dфλ = kmν (λ) e (λ) Dλ
Km in the formula is called the maximum light efficiency, which is a constant. The light flux has the same dimension as the radiation flux, but the unit of light flux is LUMEN, this unit is the most often contacted light power unit.
With the above concept, it is enough for our research color model, and then introduce some related concepts in the following:
4. Luminescent strength I: Physical quantity used to characterize the distribution of light flux emitted in the source. I = Dф / Dω Dω is a stereo element of point light source in a certain direction. I's unit: Candela, Code: Kan (CD), one of the seven basic units in the international unit system.
5, illuminance E: The amount of physical quantity used to illuminate the level of light is illuminated. E = Dф / Dσ in dσ represents one-size yuan. E 's Units: Lux (LUX), Code: Le (LX).
6. Brightness B: The physical quantity used to illuminate the light surface and the physical quantity related to the characteristics of the light-emitting surface. B = Dω / (DS CoS QDω) DS CoS Q is an apparent area of the illuminant surface element. B unit: Nit (Nit), code: Nit (NT).
