The intensity of light (both solar and artificial lighting) can vary greatly, and visually we are not able to determine the degree of illumination, because the human eye is endowed with the ability to adapt to different lighting conditions. Meanwhile, the intensity of lighting is extremely important in a wide variety of fields. For example, you can take the process of film or video, as well as, say, growing indoor plants.
The human eye perceives light waves with a length of 380 nm (purple) to 780 nm (red). Best of all, we perceive waves with a length that is just not the most suitable for plants. Bright and pleasant lighting for our eyes may not be suitable for plants in the greenhouse, which may not receive important waves for photosynthesis.
Light intensity is measured in lux. On a bright sunny afternoon in our middle lane, it reaches about 100,000 lux, and in the evening it drops to 25,000 lux. In a 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 lighting (on the southern window in the summer immediately behind the glass) is at best 3-5 thousand lux, in the middle of the room (2-3 meters from the window) - only 500 lux. This is the minimum lighting necessary for plant survival. For normal growth, even unpretentious shade-tolerant plants require at least 800 lux.
We cannot determine the intensity of light on the eye. There is a device for this, the name of which is a luxmeter. When buying it, it is necessary to clarify the wavelength measured by it, because the capabilities of the device, although wider than the capabilities of the human eye, are still limited.
Light intensity can also be measured using a camera or photo exposure meter. True, it is necessary to recalculate the received units into suites. To carry out the measurement, you need to put a white sheet of paper at the measurement site and point the camera at it, the sensitivity of which is set to 100, and the aperture to 4. Having determined the shutter speed, you should multiply its denominator by 10, the resulting value will approximately correspond to the lighting in lux. For example, with a shutter speed of 1/60 sec. lighting about 600 lux.
If you are fond of cultivating 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 a flower, the size and shape of its leaves. With a decrease in light intensity, all the most important life processes in plants are proportionally slowed down. Its quantity depends on how far the light source is, on the side of the horizon on which the window is facing, on the degree of shadowing by street trees, on the presence of curtains or blinds. The lighter the room, the more actively the plants grow 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 show, lighting is very important. High-quality shooting is possible with illumination of about 1000 lux, achieved in a television studio using special lamps. But acceptable image quality can be obtained in less light.
The lighting intensity in the studio before and during the shooting process is measured using exposure meters or high-quality color monitors that connect to the camcorder. Before shooting, it is best to walk with the exposure meter throughout the set to determine if it’s darkened or overly lit in order to avoid negative effects when viewing the footage. In addition, by correctly adjusting the lighting, you can achieve additional expressiveness of the scene and the necessary directorial effects.