Third, and as already emphasized in the preceding section, a time-honored approach to energy conservation and visual quality entails using natural light as a primary source of illumination. Daylighting diminishes not only the energy consumption but also lighting and cooling loads during highdemand hours, lowering the stress on the power grid of a city. Daylight must be brought deeper into the building to create a more balanced, complacent, and comfortable eect. Articial light needs to be varied with weather conditions, for example, when sun is shining in its full glory, articial light requirement is evidently less. During a rainy or cloudy day, more articial lighting is resorted to. erefore, such variations in the brightness level of lighting during dierent parts of a day or dierent seasons are demanded. Brightness level variations are also dependent on whether a person is working or at rest. When a person is engaged in a skilled job such as machine operation or reading, he/she may need more illumination, for which intensity control is required. Examples of the types of buildings are oces, libraries, hospitals, correctional facilities, laboratories, workshops, and so on. When the person goes to sleep, dimming control must be activated, for example, in bed rooms, and so on. Dimming may be done manually or by automatic methods. Manual control is extremely dicult. Hence, daylight or brightness sensors measuring intensity of light are essential.