Synonymous illuminance generally refers to light intensity
Definition
Light intensity refers to the energy of visible light received per unit area, referred to as illuminance, unit lux (Lux or lx). It is a physical term used to indicate the intensity of light and the amount of light that the surface area of an object is illuminated.
In photometry, "luminance" is the density of luminous intensity in a specified direction, but it is often misunderstood as illuminance. The international unit of luminosity is the candlelight accepted per square meter (called candela in Mainland China, Hong Kong and Macau).
The illumination/illuminance on a surface illuminated by light is defined as the luminous flux illuminating a unit area.
Suppose the luminous flux on the panel dS is dΦ, then the illuminance E on this panel is: E=dΦ/dS.
1lx=1lm/㎡. When an object is uniformly illuminated by light, when the luminous flux obtained on an area of 1 square meter is 1 lumen, its illuminance is 1 lux. Lumen is a unit of luminous flux.
A point light source with a luminous intensity of 1 candela has a luminous flux of "1 lumen" per unit solid angle (1 steradian).
Candela, transliterated "Candela". The concept of candlelight was first invented by the British, and it is a unit of luminous intensity.
At that time, the British used a pound of white wax to create a one-foot-long candle to define the unit of candlelight. But today’s definition has changed: heating with a black luminous body of one cubic centimeter until the luminous body melts into a liquid, 1/60 of the amount of light emitted is the standard light source, and candlelight is the standard light source. The unit of the amount of light emitted.
Terms
1. Natural lighting and artificial lighting
Sunlight is natural lighting, and light lighting is artificial lighting.
2. Illumination cycle and illumination time
In nature, 24 hours a day and night is a light cycle. The time with light is the bright period, and the time without light is the dark period. In natural light, the sunlight time (bright period) is generally calculated as the sunshine time; in artificial light, the light exposure time is the light time, and the 24h light cycle is the natural light cycle; the longer or shorter than 24h is called unnatural light Cycle; if there is only one bright period and one dark period within 24h, it is called single-period illumination; if there are two or more bright or dark periods within 24h, it is called intermittent illumination. The sum of the bright period in a photoperiod is the photoperiod.
3. Luminous intensity
The size of the luminous flux transmitted by the light source in a solid angle in a certain direction. Unit: Candela (candela, cd).
4. Luminous flux
The light energy radiated by the light source per unit time is called the luminous flux of the light source, and its unit is lumens (each point is 1 square foot which is 1 foot away from the 1 candle light source The amount of light on the area is 1 lumen).
5. Related definitions
Illumination is the degree to which an object is illuminated. That is, the ratio of the luminous flux obtained on the surface of the object to the illuminated area, the unit is lux Ix (1 lux is the illuminance produced by the luminous flux of 1 lumen evenly irradiated on an area of 1 square meter) or foot candle fc (1 foot candle is 1 The luminous flux of lumens uniformly illuminates the illuminance produced on an area of 1 square foot), 1fc=10.76lx.
Under direct sunlight in summer, the light intensity can reach 60,000~100,000lx, outdoor without sun 10,000~10,000lx, summer bright indoor 100~550lx, nighttime under full moon 0.2lx .
Incandescent lamps can emit approximately 12.56lx of light per watt, but the value varies with the size of the bulb. Small bulbs can emit more lumens and large bulbs are less. The luminous efficiency of the fluorescent lamp is 3 to 4 times that of the incandescent lamp, and the life span is 9 times that of the incandescent lamp, but the price is higher. In the light emitted by an incandescent bulb without a lampshade, about 30% of the lumens are absorbed by walls, ceilings, equipment, etc.; the poor quality and darkness of the bulb will reduce many lumens, so only about 50% of the lumens can be used. Generally, when there is a lampshade and the lamp height is 2.0～2.4m (the distance between the bulbs is 1.5 times the height), 1W bulbs per 0.37㎡ area or 2.7W bulbs on 1㎡ area can provide 10.76lx. The height of the bulb installation and the presence or absence of the lampshade have a great influence on the light intensity.
Calculation formula
Average illuminance (Eav) = total luminous flux of light source (N*Ф)*utilization factor (CU)*maintenance factor (MF)/area (㎡)
p>(Applicable to indoor or stadium lighting calculation)
Utilization factor: generally 0.4 for indoor, 0.3 for sports
Maintenance factor: generally 0.7～0.8
p>Example 1:
Indoor lighting: 4×5m room, using 9 sets of 3×36W grid lights,
Average illuminance=total luminous flux of light source×CU× MF/Area=(2500×3×9)×0.4×0.8÷4÷5=1080Lux
Conclusion: The average illuminance is above 1000Lux.
Example 2: Stadium lighting: 20×40m venue, using 60 sets of POWRSPOT1000W metal halide lamps,
Average illuminance=total luminous flux of light source×CU×MF/area=(105000× 60)×0.3×0.8÷20÷40=1890Lux
Conclusion: The average horizontal illumination is above 1500Lux.
A design case of the average illuminance of an office:
Design conditions: office length 18.2 meters, width 10.8 meters, ceiling height 2.8 meters, desktop height 0.85 meters, utilization factor 0.4, maintenance factor 0.8 , The number of lamps is 33 sets, what is the average illuminance in the office?
Lamp solution: The lamp adopts DiNiT2X55W anti-glare daylight lamp, luminous flux 3000Lm, color temperature 3000K, color rendering above Ra90.
According to the formula, it can be obtained: Eav=(33 sets X6000LmX0.4X0.8)÷(18.2mX10.8m)
=110880.00÷196.56㎡
< p>=564.10LuxRemarks: The lighting design must require accurate utilization factor, otherwise there will be a big deviation, which will affect the size of the utilization factor. There are mainly the following factors: the light distribution curve of the lamp , The light output ratio of the lamp, the indoor reflectivity, such as ceiling, wall, work desk, etc., indoor index size.
Standard value
Definition
The average illuminance on the working surface or reference plane is maintained, and the average illuminance on the surface shall not be lower than this value. It is the average illuminance on the specified surface at the moment when the lighting device must be maintained. This is the illuminance required to ensure visual safety and visual efficacy at work.
Classification
Standard values of illuminance are 0.5, 1, 2, 3, 5, 10, 15, 20, 30, 50, 75, 100, 150, 200, 300, 500 , 750, 1000, 1500, 2000, 3000, 5000lx classification.
lx (lux) is the unit of illuminance.
The standard value of illuminance is graded so that the smallest change in illuminance can be clearly felt on the subjective effect. The difference in illuminance is about 1.5 times. -The classification of 2001 is roughly the same.
Lighting national standard data
The national standard of the People’s Republic of China "Architectural Lighting Design Standard" GB50034-2013 stipulates the general illuminance standards for newly built, rebuilt and expanded residential, public and industrial buildings value.
When one or more of the following conditions are met, the illuminance of the operating surface or reference plane can be increased by one level according to the standard value of degree.
In fine workplaces with high vision requirements, when the distance between the eyes and the recognition object is greater than 500mm;
Continuous and long-term intense visual work has adverse effects on the visual organs;
p>
Recognize moving objects, when the recognition time is short and it is difficult to recognize;
When the visual operation has an important influence on the safety of operation;
When the brightness contrast of the recognized object is less than 0.3;
When the operation accuracy is high, and errors will cause a lot of losses;
When the visual ability is lower than the normal ability;
Building grade and functional requirements High time.
When one or more of the following conditions are met, the illuminance of the working surface or reference plane can be reduced by one level according to the standard value of degree.
When working for a short time;
When the precision or speed of the operation is not important;
When the building level and function requirements are low.
Under normal circumstances, the design illuminance value can have a deviation of -10%—+10% compared with the standard illuminance value.
Related instruments
Illuminance meter
The illuminance meter is a special device used to measure the level of light intensity. In some specific environments, there are strict requirements on the illuminance of light. For example, the inspection of drugs by manual has strict requirements on the illuminance of light.
Related principles
Using germanium photocells as probes, the current generated by photocells is different due to different light intensities. Then the current is amplified by DC, and then the DC is amplified by a digital-to-analog conversion circuit. The signal becomes a digital signal that directly reflects the intensity of the light.