What is the intensity of light and why is it important?

The intensity of light (both solar and artificial illumination) can vary very much, and visually we are not able to determine the degree of illumination, since the human eye is endowed with the ability to adapt to different illumination. Meanwhile, the intensity of lighting is extremely important in a wide variety of activities. For example, you can take the process of film or video, and, for example, growing indoor plants.

The human eye perceives light waves with a length of 380 nm (violet) to 780 nm (red). Best of all, we perceive waves with length, just not the most suitable for plants. Bright and pleasant lighting to our eye may not be suitable for plants in the greenhouse, which may not receive important for photosynthesis waves.

The intensity of light is measured in lux. Bright sunny midday in our mid-range it reaches about 100 000 lux, by the evening it drops to 25 000 lux. In the dense shadow its value is tenths of these values. In rooms, the intensity of sunlight is much less, because the light is weakened by trees and window panes. The brightest illumination (on the southern window in the summer just behind the panes) at the best is 3-5 thousand lux, in the middle of the room (2-3 meters from the window) - only 500 lux. This is the minimum illumination necessary for the survival of plants. For normal growth even unpretentious shade-tolerant plants require at least 800 lux.

We can not determine the intensity of light by eye. To do this, there is a device, whose name - luxmeter. At its purchase it is necessary to specify the range of waves measured by it, tk. The possibilities of the device, though wider than the capabilities of the human eye, are nevertheless limited.

The intensity of light can also be measured with a camera or a photoexponometer. However, it is necessary to make recalculation of the received units in suites. To carry out the measurement, put a white sheet of paper in the measuring location and point the camera at it, whose sensitivity is set to 100 and the aperture to 4. After determining the shutter speed, its denominator should be multiplied by 10, the resulting value will roughly correspond to that in the suites. For example, if the exposure is 1/60 sec. Lighting is about 600 lux.

If you are fond of breeding flowers and caring for them, then, of course, you know that the energy of light is vital for plants for normal photosynthesis. Light affects the growth rate, direction, development of the flower, the size and shape of its leaves. With decreasing light intensity, all the vital life processes in plants are proportionally slowed down. The amount depends on how far the light source is removed, from the horizon facing the window, from the degree of shading by street trees, from the presence of curtains or blinds. The lighter the room, the more active the growth of plants and the more they need water, heat and fertilizers. If plants grow in the shade, then they require less care.

When shooting a movie or a television program, lighting is very important. High-quality photography is possible with an illumination of the order of 1000 lux, achieved in a television studio with the help of special lamps. But acceptable image quality can be obtained even with less light.

The intensity of lighting in the studio before and during the shooting is measured using exposure meters or high-quality color monitors that connect to the camcorder. Before shooting, it is best to walk around with an exposure meter throughout the set to determine darkened or excessively lit areas of it to avoid negative phenomena when viewing the footage. In addition, the correct adjustment of lighting can achieve additional expressiveness of the filmed scene and the desired director effects.