The method of intermediate visual illuminance value of fluorescent powder LED light source with different color temperature
The vision of the human eye can make the most direct evaluation of the lighting effect. There are two types of photoreceptor cells in the human retina: cones and rods. Cone cells consist of three cells t, d, ρ with different spectral responses and low sensitivity. It works under bright conditions with a brightness of 3cd/m2 or more, and can distinguish colors and details of objects. After the light stimulus is transmitted through the optic nerve center, the spectral response to the light stimulus is called the photopic vision spectral luminous efficiency function V(λ), and its maximum response is at 555nm. Rod cells function under dark conditions with a brightness below 10-3Cd/m2. They have high photosensitivity and can only distinguish light and dark, but cannot distinguish colors and details. The corresponding spectral response is called scotopic efficiency function V' ( λ), and its maximum response value is at 507nm. The optical function under scotopic vision moves 48nm to the short-wave direction compared with the optical function under photopic vision, and the ambient brightness is between 10-3Cd/m2 and 3cd/m2, which is called intermediate vision, and the corresponding spectral response is called intermediate vision. Spectral luminous efficiency function VmU). At this time, the cone cells and rod cells on the retina work at the same time.
Vffl(A) changes with the brightness of the environment. At present, there is no definite spectral response curve for mesopic research, and the photometers used for testing electric light sources, lamps, light-emitting devices, and display devices are all based on photopic vision. According to the apparent efficiency curve, this photometer is suitable for photopic conditions and related lighting engineering design, but it will produce large deviations if used in intermediate vision environments.
At present, many lighting fields, such as road lighting, landscape lighting, or low-brightness tunnel lighting are all under the condition of intermediate vision brightness, especially in the design of road lighting, reasonable selection of lighting sources is to ensure the safety of road lighting and the key to energy saving. If the data measured by the illuminance meter corrected by the intermediate vision spectral luminous efficiency curve is used as the design basis in these lighting designs, such lighting design and implementation can be consistent with the human eye perception in these intermediate vision environments, otherwise it will cause Big deviation.
At present, the method of studying photometric value measurement under intermediate vision is mainly to use a spectrometer and a photometric probe to measure the relative spectral power distribution of the measured light and the photometric or scotopic photometry respectively, and calculate the absolute spectral power distribution of the measured light through the two. , and further calculate the mesopic photometric value of the measured light according to the mesopic model. However, this method involves a spectrometer, photopic or scotopic photometer, which is expensive, complicated to measure, and inconvenient to carry and measure.
Discussion content
The purpose of this content is to provide a method and an illuminance meter that can accurately measure the mesopic illuminance value of phosphor LED light sources with different color temperatures in the mesopic environment in order to solve the deficiencies of the above technologies.
In order to achieve the above object, a designed method for detecting the illuminance value of LED light sources with different color temperatures under intermediate vision, which includes an illuminometer probe (1) corrected by a photopic spectrum luminous efficiency function, and a data processing unit (2 ), the illuminance measuring instrument formed by the display unit (3) and the portable background luminance measuring instrument (4) or the portable reflectance measuring instrument (5). Its characteristic is to correct the intermediate visual illuminance value of fluorescent powder LED light sources with different color temperatures under different background brightness conditions L of 10_3cd/m2 to 3cd/m2, obtain a set of correction coefficients B, and store them in the illuminance meter in memory. When measuring, first measure the photopic illuminance value Ev, and then use a portable measuring instrument to measure the road surface background luminance value L; or use a reflectance meter to measure the road surface reflectance to obtain the background luminance value L corresponding to the road surface illuminance; then according to the background luminance value L, the corresponding correction coefficient B is obtained, and the corresponding intermediate vision illuminance value E_ is obtained by the conversion relationship formula Emes=B X Ev between the intermediate vision illuminance and the photopic illuminance. The correction coefficient B of a cluster of intermediate visual illuminance values under different brightness conditions of LED light sources with different color temperatures is derived according to the following formula:
Mesopic Illuminance Measurement Model:
M(x)Vm(A ) = xV(A ) + (l-x)V' (λ), 0≤x≤1(1)
In the formula: νω(λ) is the spectral luminous efficiency function of mesopic vision; χ is the proportion of photopic vision, which is a quantity between 0 and 1, which is related to the ambient brightness and the color temperature of the light source, and its values are shown in Attached Table 1 , for other color temperatures and background brightness, the X value can be obtained by calculating its relative spectral power distribution, and then interpolating the values in the table.
Phosphor powder LED light sources with different color temperatures include YAG (yellow light) LED light sources excited by blue LEDs, green and red phosphor LED light sources excited by blue LEDs, and YAG (yellow light) LED light sources excited by blue LEDs. ) light source composed of red LED, also includes blue light, green light plus red light phosphor LED light source excited by purple or ultraviolet light LED.
M(X) is the normalization constant of Vm(X ) under χ.
by formula
(1) Get the normalized mesopic spectrum luminous efficiency function ν_(λ), and obtain the peak wavelength λm at the same time, and get the mesopic efficacy Knres:
Kffles = 683/V_(555) (the denominator is the luminous efficiency value of the mesopic spectrum at 555nm)
(2) Emes = (x/683+ (I-X) (s/p/) 1699) KmesEv/M(χ) = B Ev (5)
Among them, B= (x/683+(1-x) (s/p)/1699)Kffles/M(x), s/p is the photopic and scotopic illuminance ratio of the measured light source. B is the illuminance correction coefficient of phosphor-based LED light sources with different color temperatures under different mesopic brightness.
During measurement, first measure the photopic illuminance value, then adopt the luminance meter (4) to directly measure the background luminance value, or adopt the reflectance meter (5) to measure the road surface reflectance P, and convert the relationship L=Ε*P/π by illuminance and brightness , to get the background brightness value corresponding to the light source. According to the background brightness L and the color temperature of the measured LED light source, the corresponding correction coefficient B stored in the memory of the illuminance meter can be found, and the illuminance value of the corresponding phosphor LED light source under the intermediate vision condition can be measured by Emes = BXEv FLmes0 detects the illuminance meter of the detection intermediate vision illuminance value obtained by the method for detecting the fluorescent powder LED light source of different color temperatures obtained according to the present invention under the illuminance value of the intermediate vision, and can accurately measure the illuminance value under the intermediate vision environment, reflecting The intermediate visual illuminance value observed by street lamps in the actual human eyes, thus providing a measurement basis for ensuring the safety and energy saving of road lighting.
