Illuminance Calculation Brightness Calculation

Illuminance Calculation Brightness Calculation
Accurate illuminance calculation is a very complicated problem. Its essence is the transfer of luminous flux. It includes calculation of point illuminance, calculation of surface illuminance, calculation of direct illuminance, calculation of indirect illuminance, etc., and the variable factors to be considered will also be different.

Here we focus on the calculation of the average illuminance. The concept of maintenance factor will be used in the average illuminance. This concept is relatively easy to understand, that is, with the use of lamps, their luminous flux will gradually decrease. The level of this maintenance factor is mainly related to the following factors.

The degree of light decay of the light source, because in the process of use, the light decay of the light source occurs naturally, and it will not be as bright as the beginning. If it is only calculated according to the initial luminous flux, then when the brightness of the lamp decreases, the illuminance will not be enough.

In addition, the light output of the light source is subject to maintenance, and the impact of the number of wipes is more obvious. This is relatively easy to understand. Dust, etc. will accumulate on the lampshade over time, which will also affect the light output of the lamp, and naturally affect the illuminance. , so it is also a parameter that affects the maintenance factor. The effect of cleaning the lamp once a year or several times is different.

It also includes the degree of environmental pollution, which is also easy to understand. Places with a lot of dust will naturally affect the light output of the lamps. It also includes the rate and degree of aging of the materials used in the luminaire. There are also many factors that affect the maintenance factor of lamps, such as the IP level of lamps and lanterns. It is easy to understand that if the indoor space environment is clean and the quality of the lamp light source is good, the maintenance factor of the lamp can be set higher. Therefore, the general road lighting conditions are worse, and the maintenance factor is naturally lower. Usually, the value of the maintenance factor is around 0.6, while the maintenance factor of factory lighting is higher, usually around 0.7. Home lighting usually has a better indoor environment, 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 illuminance, a parameter is often used, the utilization coefficient. 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 accurately calculating the illuminance, the relevant manufacturers will provide a table for querying the value of the utilization coefficient. Utilization coefficient is generally represented by English capital letter K.

The general formula for calculating average illuminance is

Average illuminance = luminous flux of lamps * number of lamps * maintenance factor * utilization factor / area

This method of calculating average illuminance is often referred to as the lumen method. Also because of the use of coefficient values, it can also be called the coefficient method.

Another method is that the lamp manufacturer will provide a graph to infer the number of lamps according to the graph. The reference value of the illuminance 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. Considering the light output characteristics of the light source and the change of the working surface, in fact, the illuminance of a certain point, the different illuminance of the point light source and the surface light source, the calculation is very Complicated, the exact value usually deviates from the average illuminance within a certain range, that is to say, the average illuminance only indicates the general situation of the working surface, and does not represent the illuminance of a specific point.

Brightness Calculation

Brightness is an important parameter directly related to people's feelings, but why do our general lamps describe the illuminance at most without mentioning the brightness? The value is related to the angle of the person, the distance, the reflection of the working surface, etc. There are too many uncertainties. The calculation of illuminance is relatively easy to quantify. So generally provide the illuminance.

The calculation of luminance is more complicated. To calculate the luminance accurately, computer-aided calculation is generally used now, and the known parameters are input through relevant software modeling to obtain a more accurate luminance value.