Cabin lighting choicesJan 1, 2003
Belowdecks lighting has been needed since the first day a deck was installed on a boat. One of the earliest of Thomas Edison's DC-powered incandescent electric light systems was installed on board the steamship SS Oregon in 1884. Until then all artificial lighting on vessels relied on some type of flame. While the fact that the interiors of even metal-hulled ships were made of highly combustible wood was occasionally useful when a steam-powered vessel ran out of coal, the extensive use of open flames belowdecks made electric light particularly appealing. Although many of us still like to use of an oil lamp on occasion, the reality of limited light output and generation of considerable heat makes us rely primarily on electric lighting.
Forty years ago sailors had only two choices for electric illumination sources: automobile bulbs and 12-volt filament, screw-base bulbs (the same size screw-in base as used on standard 120-volt lamps). The transistorized inverters required to power fluorescent lamps from a 12-volt supply were not within economic reach. Standard sailboat cabin lighting was very limited, and reading could be difficult unless you were mere inches from a lamp.
Things have changed for the better. We can now choose from an array of light sources. Automobile-type incandescent lamps continue to be popular for many applications, while the screw-base 12-volt lamp has become relatively expensive and is infrequently used in new construction. Fluorescent lamps, in eight-and 13-watt sizes, in single and dual lamp fixtures and powered by solid-state ballasts, have been available for the last 25 years. High-efficiency, compact fluorescent lamps and incandescent halogen and xenon lamps are increasingly popular. During the past year cold-cathode fluorescent lamps, long used in aviation and other demanding applications, have become available in fixtures designed for marine use. Light-emitting diodes, most often used as indicators as opposed to sources of general illumination, have begun to emerge as a practical light source for a limited number of applications. Yesterday's problem of too few light-source options has been overcome. Today's task is to select the best source of light for each application.
As many sailors have discovered to their dismay, the energy demand of a boat's lighting system can readily exceed the power consumption of the autopilot and sailing instruments. In many cases, the refrigeration system is the only consistently larger power consumer. We should be able to spend a quiet day and night, anchored in an attractive cove, using a reasonable amount of interior lighting, without having to run the engine or a genset to recharge the batteries.
Interior boat lighting serves three separate functions: general illumination, task lighting, and safety lighting. The amount of general illumination and the number and nature of task lights may vary widely in different parts of the boat. Safety lighting requirements are likely to be consistent throughout.
The efficiency of various light sources varies by a factor of about 8:1 when measured on the basis of lumens of light produced per watt of electrical energy consumed. Conventional tungsten filament lamps are generally the least efficient, typically yielding about 10 lumens per watt. Low-voltage halogen lamps are more efficient, producing about 14 lumens per watt. The 8-watt fluorescent lamps most often used in light fixtures sold for marine use may yield as much as 50 lumens per watt. The high-efficiency twin-tube five-, seven-, nine- and 13-watt fluorescent lamps offered in some 12-volt fixtures manage up to 70 lumens per watt, while the latest cold-cathode lamps can deliver up to 80 lumens per watt.
While the lumen output of the light is important, it cannot be the sole criterion for choosing a light source for a particular application. The size and shape of the lamp will play a large role in determining its suitability for a particular use. The color temperature of the light is an important issue. The performance of lamps when they are first turned on deserves consideration. Fluorescent lamps do not produce full light output when first started and can be difficult to start at low temperatures, operating aspects that are important in some applications. The desirability of preserving the dark adaptation of the crew's eyes should play an important part in selection of safety lighting.
General cabin lighting should be widely dispersed and as even as possible. A warm color is preferable to a cold white light. Fluorescent lights can do well for this application, provided the tubes used produce "warm-white" light, not the slightly more efficient cool-white type. The actual amount of light delivered from this type of fixture will depend largely on the design and quality of the reflector, lens, or diffuser that covers the lamp. Some of the fixtures sold for marine use are primarily designed for the recreational vehicle market and may not be ideally suited for use in a marine, saltwater environment. The life of all lamps is partly determined by how often they are turned on and off. Using fluorescent lights in the head compartment, where lights are typically used only briefly, is not an ideal application. The light may not be on long enough to reach normal output, and excessive on-off cycles shorten the life of a lamp and may affect the life of the lamp's ballast.
Twin-tube, compact fluorescent lamps can be very useful for cabin lighting. They are efficient, are available in 2,700 degree K color temperature (approximately that of incandescent lamps), and have a reasonably long operating life. These lamps are available in five-, seven-, nine- and 13-watt ratings. Although fixtures using these lamps are typically more costly than the conventional 12-volt fluorescent fixtures, they are generally of higher overall quality and are well worth considering.
A general-area light source using cold-cathode fluorescent lamps is newly available to the marine market. Cold-cathode fluorescent lamps have been used for many years, particularly in aircraft. The lamp closely resembles a neon tube, about 3/8-inch in diameter, and can be many feet in length. The electrical operation of the cold cathode lamp is explained in the sidebar on page 27. A new series of cold-cathode light fixtures, called CCF (cold-cathode fluorescent) have been introduced to the marine market by Taylorbrite, a joint venture between Taylor Made Technologies LLC, a well-known supplier to the marine industry, and Everbrite, Inc. The CCF products combine the cold-cathode lamp with a very efficient, patented lens design they call a total reflection lens (TIR). The TIR is resembles the familiar fresnel lens in its ability to capture and make the most efficient use of available light energy. Its light delivery efficiency is similar to a parabolic reflector; however, it's virtually flat, making it ideal for use in lamps installed on the overhead in boat cabins.
The combination of the lamp, lens, and a unique electronic ballast produces a highly energy-efficient light source. Available with either single or dual six-watt lamps, these fixtures deliver more useful light to the illuminated area than conventional fluorescent light fixtures. The importance of fixture design in determining the amount of light supplied per watt of power consumed is illustrated by CCF light data for fixtures equipped with the TIR lens. The most efficient fixture is a five-watt round unit that delivers 27 lux per watt at three feet when operating from a 12-volt DC power source. A single, six-watt linear fixture provides 21 lux per watt while a twin-tube, 12-watt version delivers 20 lux per watt. These data compare with about 12 to 14 lux from a nine-watt twin-tube fluorescent. Diffused lens versions of the CCF fixtures are available but necessarily deliver less light. The CCF light fixtures measure slightly less than one inch thick, a great advantage in boats where overhead clearance may be limiting. The electronic ballasts used with the cold-cathode lights automatically maintain constant light output over a wide range of input voltage variation.
Although the main lighting problem in a boat is usually obtaining sufficient light, there may be times when dimming the light may be appropriate. Conventional low-voltage fluorescent lights cannot be dimmed. CCF lamps, however, may be operated from a special dimming control that reduces total energy consumption when lamps are operated at less than full brilliance. While these new lights are not inexpensive, they appear to be well designed for marine use and offer a very useful solution to the need for maximum light per watt-hour consumed.
Reading lights, chart table lighting, inspection lights, and work lighting for use in the machinery space are all examples of task lighting. Task lights were most often designed to use bayonet-base 12-volt incandescent lamps. The design of the lamp housing and reflector of most of these lamps is far from optimum, limiting the amount of light delivered to the surface to be illuminated. The MR-16 series integral reflector halogen lamps are a superior choice for most task lighting. These lamps are composed of a small halogen lamp capsule mounted within a precisely designed dichroic reflector. A clear glass lens protects the halogen capsule. The dichroic reflector reduces the heat in the beam by allowing approximately 2/3 of the heat produced by the lamp to pass backward through the reflecting surface. This technique, along with the somewhat higher efficiency of the halogen cycle bulb, allows close use of intense light without overheating the illuminated surface or the user. Twelve-volt lamps are available in 20-, 35-, 50- and 75-watt ratings. Reflector choices include close-spot (8 degree beam width), spot (12 degree), and flood (38 degree) coverage. While light output is in the range of 17 to 20 lumens per watt, the very efficient reflectors provide 4,000 beam candlepower from a 20-watt, 12-volt lamp. The result is brilliant illumination of the work area.
A number of companies offer plug-in or screw-in halogen replacement lamps for conventional incandescent bulbs. They offer the choice of substituting a lower wattage lamp for the existing lamp while preserving the light output or by installing a lamp of the same wattage as the existing bulb, increasing the amount of light delivered. There should be no problem with fixture operating temperature, as long as the wattage of the halogen does not exceed that of the tungsten bulb being replaced.
Safety lighting is rarely given sufficient thought. The owner of a boat may be able to find his way about in total darkness; however, other crew and guests may not be as familiar with their surroundings. Every cabin or other enclosed space should have at least one general illumination light source. It will be preferable if this light can operate independently from the boat's normal electrical power system.
Virtually any useable level of illumination with light containing energy other than that of pure red light will greatly diminish or destroy the eye's dark adaptation. Many boat owners address the need for safety lighting by installing a light fixture equipped with a red-painted bulb or with a red lens. Red bulb dye or common red plastic filters do not eliminate sufficient amounts of non-red light to be useful. (Dark adaptation, achieved by excluding all except one specific color of light for a period of an hour or longer can increase the sensitivity of the eye by a factor approaching 20,000:1.)
The light emitted by red LEDs is an excellent safety lighting source. A red LED emits pure red light, usually at a wavelength of about 660 nanometers. The eye's most sensitive light sensors, the rods, are virtually blind to light of this wavelength and are therefore unaffected by even intense illumination from a red LED. The eye uses only its color-sensitive receptors, the cones, when viewing a scene illuminated by pure red light. The LED is an efficient light source for the very low level of light required for safety in a dark cabin. A single red LED rated at a light output of 5,000 minicandellas (mcd) when operating with a forward voltage of 1.8 volts and a current of 20 milliamps will provide sufficient light for a cabin sole area about six feet in diameter. It will make the entire interior of the cabin visible to a reasonably dark-adapted eye (for example, a person who has been sleeping for an hour). The current drain is low enough to make powering the light from its own battery a practical choice. A homemade, two AA battery-powered red LED safety light is easy to make. Operating life from the two AA cells should exceed 30 hours. The entire unit is light enough to mount to the overhead using a piece of adhesive-backed Velcro.
One or two of these LED lights will provide more than adequate safety lighting in a darkened cabin. They can also be used to advantage in the cockpit where they will provide enough light to eliminate the need to use a flashlight and, most important, will have no adverse effect on the ability of those on watch to see well in the dark. A multiple red-LED bicycle safety light can be purchased for less than $10 and hooked onto the hatch dodger or bimini top. aIt will illuminate the entire cockpit.