Lighting Levels

Consider that, once created, light travels onward from its source until it is modified in some way by striking whatever is in its path. Light, then, can glow, create shadows, model forms, reflect from polished surfaces, pass through translucent and transparent forms, distort shapes, be mystical and dramatic—depending upon how light is angled, diffused, and positioned. The angle of light changes the dynamic power of light—such as light from below, or light from above. All of us have seen the dramatic modeling of Frankenstein's monster's features through use of intense lighting from below.

There are four factors that affect how well we can see objects in an environment: contrast between object and background; reflectance of the object; its size or dimensions; and the length of time available to view an object. All these factors can be controlled. Time is irrelevant because it can be assumed that we will spend enough time in an area to see what is there.

Contrast, for our purposes, involves distinctions between colors and textures. For fine work, you often want sharp contrast so that object and background will not blend together. To create a relaxing mood the opposite may be desired.

Reflectance and absorption relate to the surface quality of objects in an environment—color and texture again. Matte surfaces and very dark objects absorb most of the wavelengths of light that reach them. Dark, matte-surfaced rooms will require more light than the same space in lighter surfaces.

Something to remember is that a surface which reflects less than 10 percent of the light that hits it will seem black—no matter what its color. Different surfaces reflect and absorb different wavelengths in different degrees. This selectivity determines what color we finally see. A surface that reflects primarily long wavelengths of light (when illuminated by white light) will tend to appear red because that is the wave-length that reaches our eyes. Likewise, if most of the wavelengths reflect back to our eyes, we see white. Too much light directed at glossy surfaces—like mirrors, glass tables, photographs—will produce glare. Glare is irritating to the eyes; it interferes with concentration and will induce fatigue. To avoid it, use diffuse lighting in large areas with glossy surfaces, and apply focused, directed lighting when reading or other close work is being performed. Unshaded, undiffused incandescent or fluorescent lamps are far too bright for comfort when directed at the eyes.

Visual Comfort

In residential lighting, two concerns dominate determination of illumination levels and visual comfort: function and mood of the environment. Specific tasks, such as sewing, cooking, and reading, require higher levels of lighting than do relaxation activities. Kitchen lighting should have well overall distribution, free from shadow.

Although illumination specialists discuss lighting levels in terms of foot candles or lumens, these types of measurements are impractical for measuring light in a household. We are more familiar with lighting output denoted in terms of wattage—which is the electrical power of an incandescent or a fluorescent lamp. Generally, a minimum lighting level for a living room lighting measuring sixteen feet by twenty feet, or 320 square feet, would require an overall wattage of 640 watts. This could be delivered by three lamps that provide 150 watts each or 450 together, and two others using 100-watt bulbs yielding together 200 watts. This translates into two watts per square foot or twenty watts per square meter of floor area. Use this as a rule of thumb measure, but it does not take into consideration the decorative lighting that is available. Decorative lighting often provides the added amount of illumination necessary to create a mood with lighting and achieve visual comfort.

In a room where there are very specific activities, lighting should be designed to accommodate them and provide a visual comfort. For example, in a dining room there should be direct light over the table; in a bathroom light is necessary at the mirrors; kitchen lighting should be shadow-less and evenly distributed, and there should also be extra lighting at the food preparation center. Lighting fixtures should also be focused toward the point of need, such as over the pillows of beds via wall sconces or night table lamps