Measuring principle
Photovoltaic cells are optoelectronic components that convert light energy directly into electrical energy. When the light hits the surface of the selenium photo cell, the incident light passes through the metal thin film 4 to reach the interface of the semiconductor selenium layer 2 and the metal thin film 4, and a photoelectric effect is generated at the interface. The magnitude of the generated photocurrent is proportional to the illuminance on the light-receiving surface of the photocell. At this time, if an external circuit is connected, a current will pass, and the current value is indicated from the micro-ampere meter with the lux (Lx) scale. The magnitude of the photocurrent depends on the intensity of the incident light. The illuminance meter has a shifting device, so it is possible to measure high illuminance or low illuminance. Types of illuminance meter: 1. Visual illuminance meter: Inconvenient to use, low precision, rarely used 2. Photoelectric illuminometer: commonly used selenium photometer and silicon photometer
Illumination calibration
Calibration principle:
Let Ls vertically illuminate the photocell → E=I/r2, change r to obtain the photocurrent value under different illuminance, and convert the current scale to illuminance scale by the correspondence between E and i.
Calibration method:
Using the light intensity standard lamp, change the distance between the photocell and the standard lamp under the working distance of the approximate point source, record the reading of the ammeter at each distance, and calculate the illuminance E from the inverse square law E=I/r2. This can obtain a series of photocurrent values ​​i of different illuminances, which are the curves of the photocurrent i and the illuminance E, which is the calibration curve of the illuminometer, which can be scaled by the dial of the odometer to calibrate the illuminometer.
Factors affecting the calibration curve:
The photocell and galvanometer need to be recalibrated when they are replaced; after using the illuminometer for a period of time, the calibration should be recalibrated (usually 1-2 times within one year); the high-precision illuminance meter can be calibrated with the light intensity standard lamp; The calibration range of the illuminometer can change the distance r, and different standard lamps can be used. A small-range galvanometer is selected.
Use effect
Illumination has a close relationship with people's lives. Sufficient light can protect people from accidents. Conversely, too dark light can cause fatigue in the human body far beyond the eye itself. Therefore, discomfort or poor lighting conditions are one of the main causes of accidents and fatigue. Available statistics show that about 30% of all occupational accidents are caused directly or indirectly by lack of light. The lighting requirements for the stadium (the pavilion) are very strict, and the light is too strong or too dark will affect the effect of the game.
So, what is the hygienic requirement for the indoor contrast of people living? Illuminance is a very important indicator in hygiene. Light refers to electromagnetic radiation that can cause the human eye to feel bright. The perception that can be produced when light enters the eye is called vision. The light that people see is visible light, and its wavelength ranges from 380 to 760 nm (nanometer).
Lighting can be divided into two categories: natural lighting and artificial light. Natural daylighting refers to the natural illuminance of indoors and regions, with direct sunlight scattered light and reflected light from surrounding objects, commonly expressed by daylighting coefficient and natural illuminance. The daylighting coefficient refers to the ratio of the effective area of ​​the lighting port to the floor area of ​​the room. The general house lighting coefficient 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 the indoor and the light from the outside. It also reflects the local light climate (sum of solar light illuminance indicators for natural light energy and climate).
In order to ensure that people live under appropriate lighting, China has established hygiene standards for indoor (including public places) illumination. For example, the illuminance hygiene standard of shopping malls (shops) in public places is ≥100Lx; the sanitary standard of illuminance of libraries, museums, art galleries and exhibition halls is ≥100Lx; the sanitary standard of public bathrooms is ≥50Lx; bathrooms (leaching, pool, bathing) ≥ 30Lx, sauna bathroom ≥30Lx. Foreign standards for indoor illumination, such as Germany recommended several rated light intensity, office includes 300Lx paperwork area, typing, drawing work is 750Lx; in the factory, the illuminance requirement for visual work on the production line is 1000Lx; 200Lx for hotel and public rooms; 200Lx for reception and cashier; 1500~2000Lx for shop window; 150~200Lx for hospital ward, 500Lx for emergency treatment area; 400~700Lx for school and classroom; canteen, indoor gym For 300Lx and so on.
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