An illuminance meter (or lux meter) is an instrument that specifically measures luminosity and brightness. Is to measure the light intensity (illuminance) is the degree to which the object is illuminated, that is, the ratio of the luminous flux obtained on the surface of the object to the illuminated area. Illuminance meters are usually composed of selenium photocells or silicon photocells and microammeters.
Measuring principle
Photovoltaic cells are photovoltaic elements that directly convert light energy into electrical energy. When the light hits the surface of the selenium photovoltaic cell, the incident light passes through the metal thin film 4 to reach the interface between the semiconductor selenium layer 2 and the metal thin film 4, and a photoelectric effect is generated on the interface. The magnitude of the generated photocurrent is proportional to the illuminance on the light-receiving surface of the photovoltaic cell. At this time, if an external circuit is connected, a current will flow through, and the current value is indicated on the microampere meter with lux (Lx) as the scale. The magnitude of the photocurrent depends on the intensity of the incident light. The illuminance meter has a shift device, so it can measure high illuminance and low illuminance. Types of illuminance meter: 1. Visual illuminance meter, inconvenient to use, low accuracy, rarely used; 2. Photoelectric illuminance meter, commonly used selenium photocell illuminance meter and silicon photocell illuminance meter.
Types involved
1. Visual illuminance meter: inconvenient to use, low accuracy, rarely used
2. Photoelectric illuminance meter: commonly used selenium photocell illuminance meter and silicon photocell illuminance meter
Composition and use requirements of photocell illuminance meter:
1. Composition: Micro-ammeter, shift knob, zero adjustment, terminal, photovoltaic cell, V (λ) correction filter, etc.
Commonly used selenium (Se) photocell or silicon (Si) photocell illuminance meter, also known as Lux meter
2. Use requirements: The probe of the illuminance meter is made of glass, which is easy to break and damage, and the waterproof effect is very poor when used at the same time
â‘ The photovoltaic cell should be a selenium (Se) photovoltaic cell or a silicon (Si) photovoltaic cell with good linearity; it can still maintain good stability for a long time and has high sensitivity; when it is high E, a high internal resistance photovoltaic cell is selected, and its sensitivity is low and linear , Not easily damaged by strong light
②V (λ) correction filter is included, suitable for illumination with different color temperature light source, small error
â‘¢ A cosine angle compensator (milk glass or white plastic) is added in front of the photocell. The reason is that when the incident angle is large, the photocell deviates from the cosine rule
â‘£The illuminance meter should work at or near room temperature (the drift of the photovoltaic cell changes with temperature)
Steps to use handheld illuminance meter
â‘ Turn on the power.
â‘¡ Open the lid of the photodetector and place the photodetector horizontally at the measurement position.
â‘¢Select the gear suitable for measurement.
If only "1" is displayed on the left end of the display, it means that the illuminance is excessive, you need to press the range key (⑧ key) to adjust the measurement multiple.
â‘£The illuminance meter starts to work and displays the illuminance value on the display.
⑤ The data displayed on the display constantly changes. When the displayed data is stable, press the HOLD key to lock the data.
â‘¥ Read and record the observation value displayed in the reader. The observed value is equal to the product of the number displayed in the reader and the span value.
For example: 500 is displayed on the screen, the display status is "× 2000" in the lower right corner, and the illuminance measurement value is 1000000lx, which is (500 × 2000).
⑦ Press the lock switch again to cancel the reading lock function.
⑧For each observation, read and record three consecutive times.
⑨After each measurement is completed, press the power key to cut off the power.
â‘© Put the lid of the photodetector and put it back in the box.
Use function
Illumination is closely related to people's lives. Sufficient light can prevent people from accidents. On the contrary, too dark light can cause human fatigue far more than the eyes themselves. Therefore, uncomfortable or poor lighting conditions are one of the main causes of accidents and fatigue. The available statistics show that about 30% of all occupational labor accidents are caused directly or indirectly by insufficient light. The lighting requirements for the stadium (stadium) are very strict, too strong or too dark will affect the effect of the game.
So, what are the hygienic requirements for indoor contrast in which people live? Illumination is a very important indicator in hygiene. Light refers to the electromagnetic radiation that can cause the human eyes to feel bright. When light enters the eyes, the perception can be called vision. The light that people see refers to visible light, and its wavelength range is between 380 and 760 nm (nano).
Lighting can be divided into two categories: natural lighting and artificial light sources. Natural lighting refers to the natural illuminance in the room and area. There is direct sunlight scattered light and reflected light from surrounding objects. It is commonly expressed by the lighting factor and natural illuminance. The lighting factor refers to the ratio of the effective area of ​​the lighting port to the indoor floor area. The lighting coefficient of a general house is between 1/5 and 1/15, and the living area ratio is between 1/8 and 1/10 (window area / indoor floor area). The natural illuminance coefficient is the illuminance level used to evaluate natural light. It reflects the relationship between indoor and outdoor light irradiation. It also reflects the local light climate (the sum of natural light energy and climate illuminance indicators).
In order to protect people's lives under proper light, China has formulated hygienic standards for indoor (including public places) illumination. For example, the hygienic standard of illumination in shopping malls (shops) in public places is ≥100Lx; the hygienic standard of table illumination in libraries, museums, art galleries, and exhibition halls is ≥100Lx; the hygienic standard of illumination in public bathrooms is ≥50Lx; bathroom (shower, pool, tub) 30Lx, sauna bathroom ≥30Lx. Foreign standards for indoor illuminance, such as Germany recommends several rated light intensity, office including paperwork area is 300Lx, typing, drawing work is 750Lx; the illuminance requirements for visual work in factories and production lines are 1000Lx; hotel, public room 200Lx; reception point, cashier cabinet 200Lx; shop window 1500 ~ 2000Lx; hospital ward 150 ~ 200Lx, emergency treatment area 500Lx; school, classroom 400 ~ 700Lx; cafeteria, indoor gym For 300Lx etc.
For the measurement method of illuminance, it is generally measured with an illuminance meter. The illuminance meter can measure the intensity of different wavelengths (such as the measurement of the visible light band and the ultraviolet band), which can provide people with accurate measurement results.
In short, illuminance and human health have extremely important hygienic significance for eye care.
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