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    Explain the unit lumens of luminous flux

    Lumens, the unit of luminous flux. A point light source having a luminous intensity of 1 candela (cd), the luminous flux emitted in a unit solid angle (1 steradian) is "1 lumen", the abbreviation (lm).

    Name definition

    The so-called lumens simply means the brightness of a candle one candle away from a meter. An ordinary 40-watt incandescent bulb has a luminous efficiency of about 10 lumens per watt, so it can emit 400 lumens of light. When a 40-watt incandescent lamp is 220 volts, the luminous flux is 340 lumens. Luminous flux is the ability to describe the visual response of a source of radiation in a unit of time. The unit is lumens, also known as brightness. The projector indicates that the unit of luminous flux is ANSI lumens. ANSI Lumens is the standard for measuring the luminous flux of projectors developed by the National Institute of Standardization. It measures the illuminance of each point on the nine intersections of the screen "Tian", multiplied by the area, and then nine. The average of the points is the ANSI lumens of the projector. The higher the lumen value, the brighter it is, and the higher the brightness, the less the light needs to be turned off when projecting. ANSI is an abbreviation for American National Standards Institute.

    Detailed introduction

    Again, this amount is for the light source, is the size of the total amount of light emitted by the light source, and is equivalent to the optical power. The greater the luminous flux of the light source, the more light is emitted.

    For isotropic light (ie, the light from the source is emitted at the same density in all directions), then F = 4?€I. That is, if the I of the light source is 1 cd, the total luminous flux is 4?€ = 12.56 lm. Compared with the mechanical unit, the luminous flux is equivalent to the pressure, and the luminous intensity is equivalent to the pressure. If the spot to be illuminated looks brighter, we must not only increase the luminous flux, but also increase the means of convergence. In fact, it is to reduce the area so that we can get more intensity.

    It is important to know that luminous flux is also artificial. It may not be the same for other animals, and it is not completely natural, because this definition is based entirely on the human eye's response to light.

    The human eye feels differently for different colors of light, and this feeling determines the conversion relationship between luminous flux and optical power. For the most sensitive 555 nm yellow-green light of the human eye, 1W = 683 lm, that is, the power of 1W is all converted into light with a wavelength of 555 nm, which is 683 lumens. This is the maximum light conversion efficiency and is also the calibration value because the human eye is most sensitive to 555 nm light. For other colors of light, such as 650 nm red, 1 W of light is only equivalent to 73 lumens, which is because the human eye is not sensitive to red light. For white light, it depends on the situation, because the light of many different spectral structures is white. For example, white light from LEDs , white light on television, and daylight vary widely, with different spectra.

    As for the luminous efficiency of the electric light source, it is another related topic, which is to say how much luminous flux can be converted into 1W electric power. If all is converted to 555nm light, it is 683 lumens per watt. But if half of it is converted to 555nm light and the other half becomes heat loss, the efficiency is 341.5 lumens per watt. Incandescent lamps can reach 1W = 20 lm, and the rest are heat or infrared. To measure the luminous flux of an irregular illuminator, it is more professional and complicated to use the integrating sphere.

    The approximate efficiency of common luminescence (lumen/watt)

    Incandescent lamp, 15
    White LED, 80-200
    Fluorescent lamp, 50
    Sun light, 94
    Sodium lamp, 120
    Energy saving lamp, 60-80
    LED, 80-130

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