Introduction to the knowledge of light source for

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Introduction to light sources for spectrum

light sources refer to objects that can emit electromagnetic waves within a certain wavelength range (including visible light, ultraviolet light, infrared light, X-ray and other invisible light). Usually refers to a luminous body that emits visible light. All objects that can emit light by themselves are called light sources, also known as luminaries, such as the sun, stars, lamps and burning substances. However, people can only see the moon surface and desktop by reflecting external light. Such reflected objects cannot be called light sources. Visible light sources are indispensable in our daily life. Visible light and invisible light sources are also widely used in industry, agriculture, medicine and national defense modernization

visible light sources often improve the concentration of enterprises for daily lighting or display signals; Invisible light source is usually used for medical treatment, communication, night photography and other special purposes. The study of light source spectrum can also analyze the structure and composition of luminous substances

light sources are mainly divided into: thermal radiation light sources, such as the sun and incandescent lamps; Gas discharge light source, such as carbon lamp, mercury lamp, fluorescent lamp, etc. Laser is a new type of light source, which has the characteristics of concentrated emission direction, high brightness, excellent coherence and good monochromaticity. ● how to select the appropriate light source? Flange ball valve

select the appropriate light source, and first determine the wavelength range to be used. Zhuo Lihan light can provide a variety of light sources such as deuterium lamp, bromine tungsten lamp, xenon lamp and infrared light source. The wavelength range covered by various light sources is shown in the following figure:

◆ xenon lamp: nm (nm)

◇ it has very high radiance, and the color temperature is as high as 6000k

(1) the oil viscosity is too small or too dirty ◇ the luminous area is small, which is easy to be used for collimating beam

◇ the spectrum coverage is wide

◇ the design structure of the back reflector, It can improve the light use efficiency by more than 50%

◇ the UV band has high output energy and is suitable for being used as an excitation light source

◇ it can be used to simulate the solar spectrum ◆ deuterium lamp: nm

◇ very efficient UV light source

◇ the spectrum in the UV band is smooth

◇ it has multiple characteristic spectrum peaks, It can be used as a wavelength calibration light source ◆ tungsten bromide lamp: nm (nm)

◇ it has high output stability

◇ wide spectral coverage

◇ the design structure of the back mirror can improve the light efficiency by more than 50%.

◇ the spectrum is continuous and smooth within the full spectrum

◇ it can be used to calibrate as a standard white light source

◆ infrared light source: μ M

◇ wide spectrum coverage ◇ long service life ◇ other light sources:

◇ low pressure mercury lamp light source: it has multiple characteristic peaks, which are used for wavelength correction of spectral instruments, or as ultraviolet excitation light source

◇ spectral radiance standard light source: it is used for response correction of spectral instrument system

◇ sunlight simulator: it is used to simulate sunlight

◇ composite light source: according to the needs of spectrum coverage, It is composed of two lamps through optical path optimization. It can also design more than two

bulb composite optical paths according to customers' needs. For details, please contact the Sales Department of the company. ● key performance indicators of light source ◆ spectral range

when selecting a light source, especially in spectral applications, spectral range is the first consideration. At the same time, it should be noted that the light source to be selected has a high light output efficiency within the required spectral range as far as possible, and a low light output efficiency within the unwanted spectral range, because the unwanted part of the spectrum will cause the problem of stray light

in addition, if transmission, reflection/absorption spectra are used, it should be noted that the spectrum with smooth spectral curve within the measurement range must be selected. For example, when making the reflection spectrum within the nm spectral range, only in terms of the spectral range, xenon lamp (nm) and bromine tungsten lamp (nm) meet the requirements. However, from the perspective of actual measurement, because xenon lamp has more sharp spectral peaks within this range, the measurement will be inaccurate. Therefore, the bromine tungsten lamp with smooth spectral line should be selected for measurement. (please refer to page 7 for spectral radiance curve) ◆ radiation power

generally, the radiation power under actual use conditions should be considered when selecting the light source power, which not only has the factor of output power, but also has the influence of the size of light-emitting area, light receiving efficiency, etc. For example, when comparing the radiation power that 75W xenon lamp and 150W xenon lamp can generate at the same spatial position without considering the influence of factors such as light receiving efficiency, 75W xenon lamp is 2.7 times that of 150W xenon lamp. This is because although the output power of the former is only half of that of the latter, the luminous area (ARC) of the latter is 8.8 times that of the former, so the power density at the same spatial position is small

therefore, when selecting a light source, we should not only consider the output power of the light source, but also consider other factors, especially the influence of the radiation power density caused by the size of the light spot. Generally, we can improve the light collection efficiency by selecting an appropriate light receiving system

the unit of spectral radiance is usually: W M-3 sr-1nm-1, or W m-2 nm-1. The difference is actually the stereoscopic angle of light receiving (as shown in the figure), which corresponds to the relative aperture number of light receiving system (such as lens), and is called the light receiving coefficient

example: in a 150W xenon lamp light source system with a light receiving coefficient of 0.05, calculate the spectral radiation power that can be obtained in the nm range. From the spectral radiance curve, it can be found that the spectral radiance in this range is about 15m w m-2 nm-1, the light receiving coefficient is 0.05, and the spectral bandwidth is 200nm. Due to the use of the back mirror structure, the light efficiency is improved by 50%, so the total output light radiation power is about 15 × zero point zero five × two hundred × (1+50%)=225mW。

can not be separated from the help of material solutions. In addition, it can be seen from the spectral radiance curve (Page7) that for the same type of light source, the spectral radiance difference is not large when the power is different. Therefore, in the spectral system, the signal intensity cannot be improved simply by improving the power of the light source. It is also necessary to comprehensively consider the collection efficiency of the light source. In the optimized light source collection system, the light source with low power consumption can often be used to replace the light source with high power consumption. ◆ total output power in most applications with large radiation area, total output power is more important. ◆ size and shape of the light emitting area the size and shape of the light emitting area of the light source are selected in order to obtain a more matching spot shape with the target area, so as to improve the actual use efficiency of the light source. For example, the long light spot is more suitable for the slit design of the spectrometer. ◆ uniformity and stability of light source for some optical measurements, high spatial uniformity and time stability are required, so special optical design and power supply design are required. For example, the characteristic measurement of solar cells. Generally speaking, the light source stability of bromine tungsten lamp is better than that of xenon lamp and other arc discharge light sources. ◆ main characteristics and index parameters of the sunlight simulator the sunlight simulator is a light source used to simulate sunlight, with high solar spectrum matching degree, spatial uniformity and time stability. The standard solar spectrum and the solar spectrum penetrating the atmosphere to the earth's surface are as follows:

according to relevant international standards, the optical power density of about 1000w/m2 (@am1.5g filter) is called a solar constant. The spectral matching degree, time stability and spot uniformity corresponding to different levels of the sunlight simulator are shown in the following table (according to IEC regulations):

◆ color temperature (T)

in order to represent the color property of the light emitted by a thermal radiation light source, the color temperature is commonly used, and the unit is K. Color temperature refers to the temperature of blackbody with the same radiation ratio as that of thermal radiation light source at the specified two wave lengths. The impact resistance of Se Wendi panlite polycarbonate is 200 times that of glass, not the temperature of the thermal radiation light source itself

since the color temperature is compared according to the radiation ratio at the specified two wavelengths, the continuous spectrum of thermal radiation sources with the same color temperature may also be different. If the specified wavelengths are different, the color temperature is often different. As for the non thermal radiation light source, the color temperature can only give a general picture of the light color of the light source. Generally speaking, high color temperature means more blue and green light components, while low color temperature means more orange and red light components. ◆ wavelength corresponding to the maximum value of monochromatic radiation emittance according to Wien's displacement law λ M is inversely proportional to the color temperature T: λ m·T=2898( μ m·K)

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