VISION AND LIGHTING

It is an unfortunate reality that bad lighting is all to common. It may result from simple carelessness or indifference, but it can also come about in planned situations, even when handbook recommendations or manufacturers' advice is followed. The design in lighting is too often limited to providing a high level of light, with the assumption that this will take care of all users' needs. However, seeing depends on many additional factors- shading and shadow, limitation of brightness contract, color quality- that, along with level of intensity, make seeing easy and satisfying. To understand the complexities of theses issues, it is necessary to consider the basics of human vision, the send that lighting is after all intended to serve.

Almost everyone had at some time studied, at least briefly, the physiology of the human eye and can recall something of its mechanics,. the familiar analogy with a simple camera still serves to explain it. The eye itself is the dark chamber comparable to the box or bellows of the cameras; the retina at the back of the eye is the light-sensitive surface comparable to the film or place of photography. The pupil of the eye is the lens that can change focus to form a sharp image on the retina of objects near or far away. The retinal image is transmitted though the optic nerve to the rain, which interprets the image to create the mental picture that we see. The image is, of course, in color and it is in sharp focus only at its center. Through the movements of the eyeball, head and body, the eye scans the scene before it and builds up a mental image that includes a wider, more focused field of view than the eye itself can generate at a given moment.

As it focuses on individual objects, what the eye sees depends on the kind and quality of light available. Light bouncing off objects reflects back to the eye variations in brightness and color that correspond in a complex geometric way with the size, shape, distance, color and texture of those objects. this creates on the retina the picture on perspective that we learn to understand as being the appearance of whatever we look at.

CONSIDERATIONS FOR GOOD LIGHTING

The goals of lighting are to promote good visibility and to generate qualities of atmosphere, the aesthetic and emotional impressions that convey a mood appropriate to the space in question, Theses goals may be in conflict, as in the restaurant where the dim candlelight mood" lighting creates a pleasant atmosphere but makes it difficult or impossible to read the menu or cut the steak. No single lighting setup will answer each of these activities. Therefore, means if varying the lighting must be found. For every task and every situation,the following issues must be faced.

Light Level: This is simple quantity of light at a task, which is easily measured. The eye is equipped to adjust to the extremes presented by natural light, from the brilliant noonday sun to dim starlight or less.

Control of Brightness Contrast and Glare: The adjustment of the iris and reina-optic-nerve-brain system cannot deal with a visual field that includes bright and dim areas that both demand attention, as when trying to read while facing a bright window. When the difference between the brightest and dimmest points within a visual field is not extreme, the eye need not struggle to find a compromise adjustment.

Contrast and Diffusion: Shade and shadow emphasize form but conceal detail in the shaded areas. Light that comes from a concentrated space, or point source, tends to create strong shade and shadow, while discussed light tends to diminish or block out shading.

Economic Issues: Daylight is free, but windows and skylights are not. Moreover, windows and skylights admit summer heat and allow winter heat to escape, effects which must be offset with mechanical equipment that is costly to provide and operate.