1: KNOW HOW LIGHTING TECHNOLOGY WORKS
To work effectively with lighting designers, you need a quick introduction to lighting technology.
A couple of technical terms first:
In the lighting trade, bulbs are called "lamps." This can lead to some real confusion. When talking with designers, try to avoid using the word "lamp" to refer to a lighting fixture, or be specific by saying "table lamp" or "floor lamp."
Some types of lamps require what are called "ballasts." These are small transformers that raise household voltage to levels high enough to activate the lamps. (Ballasts are the gadgets that provided pleasant interruptions to the school day when they went bad and black tarry gunk dripped down from the light fixtures onto student desks during boring classes.)
Lamp shapes are designated by letters, followed by a number that stands for the diameter of the lamp in eighths of an inch. Some everyday letter designations include:
A - Standard everyday lamps T - Tube, such as fluorescent lamps R - Reflector flood PAR - Parabolic aluminized reflector (these are as subtle as headlights)
With the exception of LEDs (light emitting diodes, which are used in modern exit signs) there are three major types of sources of artificial light used in libraries—incandescent, fluorescent, and HID.
Incandescent
Incandescent lighting is the system we know best. Some people call it a "hot wire in a bottle." It's not the first method invented to create electric light, but it's the first practical one for daily use in buildings.
Incandescent lamps come in a vast variety of shapes and sizes—everything from ordinary round bulbs to all sorts of spotlights and other specialized shapes.
What are the main characteristics of incandescent light?
Inefficient
Incandescent light provides relatively little light per watt. For most of us, that's just an economic choice, but some states have laws limiting the amount of lighting wattage per square foot in public buildings. Most standards of this type will make it impossible to use incandescent lamps and still produce sufficient light.
Extremely standard technology
There's nothing tricky about many incandescent lamps.
Accurate color rendition
Because incandescent light is created by heating a filament until it glows, it is a form of "black body radiation" and has all of the wavelengths of visible light. The effect is almost always pleasant.
Warm color temperature
Most incandescent lighting is warmer in color than daylight, but our eyes adjust easily to the difference, which becomes almost unnoticeable when we cannot compare incandescent light and daylight simultaneously.
Controllable
Incandescent light is easy to control. It can be focused for projection or spot illumination. It is easy to adjust the intensity with inexpensive dimmers. An immense variety of special-purpose lamps is available to meet all sorts of special needs.
Concentrated
Incandescent light is too concentrated for most library lighting situations. Trying to provide even, low-glare lighting in large areas is almost impossible with incandescent sources.
Quartz halogen lamps are bright incandescent lamps with a cooler, "whiter" color. This is achieved by allowing the lamp filament to burn at a higher temperature. The name comes from two essential components—a quartz envelope, which can withstand the higher temperature, and halogens inside the lamp, which prevent the filament from burning out. The surfaces of quartz halogen lamps can be extremely hot, and the light is very concentrated. We feel that their best use is for projectors and for jewelry showcases rather than for library illumination.
Fluorescent
In fluorescent lamps, ultraviolet light falls on phosphors that line the insides of the tubes. The phosphors convert UV light to visible light. The quality of phosphors varies a lot—compare, for example, very early color TV with modern color TV.
Fluorescent lights all require ballasts.
Fluorescent lighting has become standard for offices and other spaces requiring bright, uniform light.
Fluorescent lamps are described by the diameter of the tube, given in eighths of an inch. For example, the old-fashioned T-12 lamps are 1½ inches in diameter. Most modern lamps are T-8s or T-5s. This is the way lighting people describe them, so it's good to know what they're talking about.
The basic characteristics of fluorescent light are:
Efficient
The light output per watt with fluorescent light is several times greater than with incandescent light, and about comparable with HID Lighting
Wide variation in accuracy of color rendition among lamp types
When you select fluorescent lighting for your library—and it's almost always the right decision—be sure to specify a high level of color rendition (at least 85 CRI, as described later in this material).
You will also want to specify color temperature. Many libraries like a temperature of about 3500° Kelvin, which blends quite well with incandescent light and gives libraries a warm, inviting look after dark.
Once you have specified exact lamp types, be sure that no other types are intermixed with them. We have all seen piebald fluorescent fixtures with a variety of odd colors of lamps, and the effect is wretched. Avoid this by settling on one phosphor type from one manufacturer.
Variety of lamp shapes
Standard fluorescent lamps are 4-foot tubes and make a good basic lighting system for a library, although some fixtures, such as pendant bowl fixtures, use banks of shorter lamps. Some modern fixtures have fluorescent tubes bent in loops—so called "biax" lamps. These can be fairly large, as in some parabolic fixtures, or quite small, as in some (desirable) suspended bowl fixtures or (undesirable) recessed downlights.
Standard technology
Fluorescent technology has been around for nearly two-thirds of a century. If you stick with standard lamp shapes, supplies will be cheap and all of your workers will be at home with maintenance needs.
Silent ballasts available.
Everyone has experienced ballast hum. In some libraries with older fixtures, the noise can be amazingly irritating.
One of best ways to avoid ballast hum is by using electronic ballasts.
In addition to the benefits of silence, electronic ballasts save a considerable amount of energy—about 8 watts for every pair of 4-foot lamps. If your library has 750 4-foot lamps, you will save 6,000 watts (plus an additional 2,000 watts in air conditioning load, since every watt saved in lighting saves about 1/3 of a watt in AC).
Electronic ballasts also reduce what some people find an annoying flicker in fluorescent lights, because the electronic ballasts operate at far higher frequencies than magnetic ballasts.
Regardless of which ballasts you select, always specify that they should be "sound rated A."
High Intensity Discharge
The HID family includes mercury vapor, sodium vapor, and metal halide. Unlike the first two, metal halide lamps have phosphors like fluorescent lamps. Invisible ultraviolet light created by the lamp strikes phosphors, which convert it to visible light.
Everyone is familiar with exterior HID lighting. As the purplish mercury vapor lights have been replaced by sodium vapor, the world of night is increasingly an orange one. In fact, many cities look orange from the air at night.
Metal halide lamps have better color rendition than mercury vapor and sodium vapor, and this has led to their use in libraries and other non-industrial locations.
Characteristics of HID lighting:
Very efficient and concentrated
Like fluorescent lamps, HID lamps produce a great deal of light per watt.
Because relatively small HID lamps can emit a great deal of light, designers find them attractive for small fixtures lighting large spaces. However, modern T-5 fluorescent lamps also are also extremely bright and compact.
Restrike time
A major problem with HID lighting is "restrike time." When you turn an HID lamp off, it has to cool off and then warm up again before you can turn it back on.
This is annoying under everyday circumstances and disastrous in meeting rooms, where we want to turn lights back on immediately at the end of programs.
Problems with color maintenance
Libraries with metal halide lamps have noticed that—even if a batch of metal halide lamps all come from the same box—the colors may be different. And as the bulbs age, they tend to get worse. We've seen many libraries where a series of identical HID light fixtures vary in color from gray to green to blue to lavender to even bright raspberry.
Librarians often complain that they can open a new carton of lamps, use them to replace all the lamps in a row of ceiling fixtures, and watch the light from the lamps turn all sorts of colors over the next few weeks or months.
Lamp manufacturers are working on the problem, but it hasn't been solved. (Ceramic metal halide lamps represent one approach to the problem.)
Typically noisy ballasts
Ballast hum is particularly pronounced with HID lighting. Frequently, ballasts must be located remotely in order to avoid driving readers and staff up the wall. And sometimes they can still be heard.
Fairly standard technology
There are lots of HID lighting fixtures out there, but be prepared for little or no flexibility in selection of lamps for individual fixtures. HID lamps and ballasts are matched, and substitution of different lamps is usually not an option.
Catastrophic end of service
Problems can result from the high heat and pressure in HID lamps. For example, we have seen fixtures with plastic globes where pieces of material had melted off the lamp housing and fused permanently to the globes. The result is strikingly convincing representation of dead bugs.
Even a greater problem comes from the very occasional tendency of HID lamps to explode—the so-called "catastrophic end of service." When this happens, bits of blazingly hot glass can rain down on the people below.
Best choice
With the current state of technology, we believe that the best choice for indoor use in libraries is always fluorescent. It offers the best combination of features:
* Color maintenance * High CRI available * Silent ballasts available * Quick start * Limited dimming available (but not theatrical quality) * Very traditional technology * And now sufficient compactness with T-5 lamps
Types of fixtures
An amazingly complex variety of fixtures is available, and you will want to work intensively with your designer to select the ones best for your library.
Here are a few basic pointers.
Uplight
Uplighting involves directing light upwards toward a white ceiling, from which it is reflected to light the areas below.
In libraries, uplight is always vastly preferable to downlight. It is far more evenly distributed, and it leads to far lower glare. Always specify uplighting for your library.
Some fixtures are designed to bounce 100 percent of their light off the ceiling, while others have a downlight component of perhaps 30 percent. We prefer 100 percent uplight, since it reduces veiling reflectance (see the section on glare) to a minimum.
One use where mixed up and downlight works well is lighting historic libraries. In this kind of situation, uplight provides the actual working light, while ornamental fixtures with low-wattage bulbs provide a traditional "feel" and give the impression that they are the actual source of light. In such circumstances, we prefer the low-wattage bulbs to be just perceptibly brighter than the ceiling behind them.
Downlight
Downlighting involves shining light directly on areas to be illuminated.
Many fixtures are designed for downlighting.
One very standard type of fixture is the so-called "troffer," a rectangular fixture fitted flush into the gridwork of a suspended ceiling. Troffers with various types of lenses are found everywhere in offices. If your office ceilings are low (less than about 10 feet) you'll be stuck with troffers, but they're a far poorer choice than uplighting.
If you install troffers in your library, be sure to avoid those with parabolic wedge lenses—metallized plastic grids with small square openings. These lenses direct all of the light straight down, leading to dark walls and ceilings, poorly lighted book spines, harsh shadows, and a general aura of gloom and glare. We've seen them in many libraries, and they are always a very serious mistake.
Recessed downlights
Recessed downlights, otherwise known as "can lights," are the bane of many libraries, one of the truly evil ways to attempt to illuminate libraries. Can lights have many unpleasant characteristics, including:
* High glare. * Inefficiency (except for fluorescent can lights). * Spotty illumination. * Unpleasant shadows. * Unpleasant brightness. Looking upward into a can light while you're scanning the top shelves is a particularly nasty experience. * Because of the high concentration of light, unpleasantly dark ceilings. * Odd and unattractive patterns of light and dark along walls.
If you are building a library, the chance is about 100 to 1 that your designer will recommend at least some can lights. Head this vile tendency off at the pass by specifying in advance that there will be absolutely no can lights anywhere in your library.
Actually, there are a couple of good uses for can lights. One is single lights shining on the floor inside the entrances to meeting rooms. If these are kept dimmed to a very low level, they will help people arriving in dark rooms to see where they are standing while their eyes adjust to the dark.
Indirect/direct fixtures
A number of fluorescent fixtures exist that supposedly combine direct and indirect. They have baffles that prevent one from seeing the actual lamps inside the fixtures. Both troffer and suspended fixtures of this type exist. Most of the time, these fixtures are used in areas with ceilings lower than 10 feet, but some designers just like the look. Depending on their design, the fixtures are called "recessed indirect" or "direct/indirect." We think they're better than more direct fixtures, but not much better, and they're still vastly inferior to reflected uplight.
Lighting stacks
If your ceiling is too low for uplighting, be sure that your strips of downlights are perpendicular to your stack aisles. This insures that light shines into every aisle, regardless of how you alter aisle width. Far too many libraries have strips of downlights installed parallel to stack aisles, with some fixtures centered over aisles (good) and others directly above stack units (bad).
In summary
In our opinion, fluorescent lights provide the most reliable, inexpensive, and easily-maintained lighting. With modern versions (such as T-5s) they can replace HID lamps in small fixtures and still provide a great deal of light. For modern libraries, 100 percent uplighting is by far the best. For historic structures, some downlighting may improve the historic feel of the building.
We recommend that you specify "fluorescent 100 percent uplighting" at the start of your project and demand that your designers defend in detail each variation.
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