What is illuminance? How to calculate the illuminance of lighting fixtures? Ans what is brightness calculation? Here let’s talk about some basic knowledge of lighting illuminance calculation and brightness calculation.
Accurate illuminance calculation is a very complicated problem. Its essence is the transfer of luminous flux. It includes point illuminance calculation, area illuminance calculation, direct illuminance calculation, and indirect illuminance calculation, etc. The variable factors that need to be considered will also be different.
Here we focus on the calculation of average illuminance. The concept of maintenance coefficient is used in the average illuminance. This concept is easier to understand, that is, as the lamp is used, its luminous flux will gradually decrease. The level of this maintenance factor is mainly related to the following factors.
The degree of light decay. The light source decay occurs naturally during the using process, and the luminaire will not be as bright as it was at the beginning. If it is only calculated according to the initial luminous flux, then the illuminance will not be enough when the brightness of the lamp decreases.
In addition, the dust in the air will also affect the amount of light emitted by the lamp, which naturally affects the illuminance. So it is also a parameter that affects the maintenance coefficient. The effect of wiping the lamp once or several times a year is different.
It also includes the degree of environmental pollution, which is also easy to understand. A place with a lot of dust will naturally affect the light output of the lamp. It also includes the aging of the materials used in the lamps. There are many other factors, such as the IP rating of the lamps, which are the factors that affect the maintenance factor of the lamps. It is easy to understand that if the indoor space is clean and the light source is of good quality, the maintenance factor of the lamp can be set higher. Therefore, the general road lighting conditions are not so good, and the maintenance factor is naturally lower. Usually, the value of the maintenance factor is about 0.6, while the maintenance factor of factory lighting is higher, usually about 0.7. The indoor environment of home lighting is usually better, and the maintenance factor is generally set at Around 0.7-0.8.
The maintenance factor is generally represented by the uppercase English letter K.
When calculating the illuminance, a parameter is often used, the utilization factor. The utilization factor is mainly related to the size of the illuminated space and the reflective material of the wall. For example, if the reflectivity of the ceiling, wall, and floor is higher, the value of the natural utilization factor may be higher. When calculating the illuminance accurately, the relevant manufacturer will provide a table for querying the value of the utilization factor. Then the general formula for calculating the average illuminance is
Average illuminance = luminous flux of lamps * number of lamps * maintenance factor * utilization factor/area
This method of calculating the average illuminance is usually called the lumen method. Also because of the coefficient value used, it can also be called the coefficient method.
In addition, there is another method. The luminaire manufacturer will provide a graph to infer the number of luminaires based on the graph. The illuminance reference value of this graph is generally 100lx, which is suitable for general lighting.
We have also seen that this is to calculate the average illuminance, which is a simplified calculation. Taking into account the light output characteristics of the light source and the change of the working surface, the calculation is actually very specific and complex to the different illuminance of a certain point, the illuminance of the point light source, and the surface light source. Its accurate value usually has a certain range of deviation from the average illuminance, that is to say, the average illuminance only represents the general situation of the working surface, and does not represent the illuminance of a specific point.
Brightness is an important parameter directly related to human experience, but why do our general lamps describe the illuminance at most without mentioning the brightness? This is because the brightness calculation must be after the calculation of the illuminance. Regarding the brightness, the value is related to the angle of the person stands, the distance, the reflection of the working surface, and so on.
The calculation of brightness is more complicated. For the brightness to be calculated accurately computer-aided calculations are generally used now.
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