Sponsored by Good Old Boat Magazine
Modern lighting projects for cruising sailboats
by Cade Johnson
We began tinkering with LED lighting in our boat several years ago. Since then we have completed numerous small lighting projects and have discussed the topic of LED lighting with other cruisers. What follows is a distillation of our experiences.
LEDs are light-emitting diodes. A diode is a device that passes electric current in only one direction. In a diode, electrons encounter a transition from one type of conductor
(P material) to another (N material) and at this transition they abruptly experience a drop in energy. In an LED, the energy drop is great enough to form a photon of visible light. If an electron were to enter the LED from the other direction (simplistically speaking), it would encounter an energy rise and would not have sufficient energy to pass the rise. No current could flow.
The two types of semiconductor material (P and N) in an LED are joined together and connected to the external world by tiny wires, which in turn connect to larger copper leads. (Often these leads contain solder blocks near the housing for stopping the leads against a circuit board.) The diode, its reflector, and its tiny connection wires are placed into a tiny reflective dish. This assembly is sealed in clear epoxy plastic. The top of the clear plastic is formed into a rounded shape to act as a lens, and the copper leads exit from the bottom of the plastic. The emitted light is directed by the reflective dish to the lens and focused into a beam. Early LEDs had to have this focusing because they did not produce much light. The design has been retained for the more modern and much brighter cousins, the ultrabright LEDs.
Advantages of LEDs
Because of the way they produce light, LEDs are very energy-efficient. Almost no heat is released. A simple 12-volt reading-light circuit can be built that will consume only 20 milliamps (abbreviated mA and equivalent to 0.020 amps, or less than 0.5 amp-hour per day). It is still generally possible to get more light per watt from fluorescent bulbs, but sometimes one does not need the amount or quality of light that fluorescent bulbs produce. Because of the way they are constructed, LEDs project their light in a relatively narrow beam, so a bright beam is focused into a relatively small area. This can be an advantage -- there is no need to use external reflectors or lenses to direct a sharp beam, but if more diffuse light is needed, it is relatively easier to scatter light than to focus it. (For example, roughen the LED lens with some 120-grit sandpaper, and the light will be considerably diffused -- no optics expertise required.)
LEDs come in a variety of colors; it can be fun mixing colors to create a festive atmosphere. Furthermore, a range of colors creates a broader available light spectrum, making it easier to discern the true color of objects that are illuminated by the light.
LEDs have an estimated lifetime of about 100,000 hours; if an LED reading light is in use every night of the year for two hours, it could theoretically last 130 years. Manufacturers did not come up with that 100,000-hour duration by measuring how long LEDs last on boats, but nonetheless an LED light cluster has the potential to be very durable. LEDs do lose intensity with age, which is why most boating LED lights are rated at 50,000 hours (or 5.7 years of continuous use).
LEDs are relatively expensive. Although the price is declining, ultrabright white LEDs are still more than $2 each unless purchased in bulk. And they were not designed for use on boats. The electrical connections to an LED are slender copper wires that have been coated with electrical solder; they are not very resistant to corrosion.
LEDs typically emit light of a very narrow frequency range -- the colors are very pure. Because of the narrow spectrum, objects they illuminate will appear either the color of the LED or black. If you want to read a chart, for example, it may be difficult to distinguish various shades of blue under a red LED, as all will appear black. This can be addressed by always including a white LED in a cluster or at least mixing a couple of specific colors to broaden the emitted spectrum a little.
White LEDs, unlike all the other types, emit a relatively broad spectrum of colors. They do this because they are really blue LEDs "in disguise," with a phosphor coating like an old black-and-white TV screen. The blue light excites the phosphor coating, and the phosphor then emits a range of different lower-energy photons of light. Most white LEDs have a bluish cast, which can make food unattractive but is good for reading printed material. Some of the newest white LEDs have a slightly yellow cast like an incandescent light.
Although LEDs can produce an intense beam, their total light output is quite low. If a small screw is lost on the cabin floor at night, overhead LED lighting will not serve for the search. Sometimes a brighter light is required, such as a conventional incandescent bulb. We have modified our overhead lights with two-way, center-off switches so we can turn on the dim LEDs or switch to the old incandescent lamps, if necessary.
LEDs are delicate electronic devices that can be easily destroyed if mishandled. For example, they must not be overheated or the two different conducting materials may become separated and the LED will no longer function. The most likely ways to overheat an LED are by passing too much current through it or by overheating it when making a solder connection.
Designing an LED project
We use LED lights on our boat for low ambient light in the main cabin and the cockpit, as a spare anchor light, as reading lights, as our chart table lighting, as a replacement light for failed instrumentation lights, and as auxiliary lighting in the galley.
When contemplating a boating lighting project, it may be helpful to review the well-thought-out lamp selection guide at the Alpenglow Marine Lights website (<http://www.alpenglowlights.com>). Although Alpenglow does not make LED-based light fixtures and considers LEDs a less-than-optimal lighting choice, the company's ideas about planning lighting in general are useful. For instance, LEDs can project a narrow and intense beam of light or they can produce a diffuse, but dim, glow more like other lighting sources. Both types of lighting may be needed at times. It is pleasant to sit and chat with friends in low diffuse light, but a more focused beam is necessary for reading or doing detailed work.
LEDs of the ultrabright variety come in red, amber, green, blue-green, blue, and white. We have found that a mix of colors is better than a monochrome light in every case. The eye works better with a range of colors even if the colors are dim. All LED colors have a frosty or cool tone, so always include an amber LED in the mix to warm up the appearance of the light.
Ultrabright LEDs differ from regular indicator lights, such as may be found on the front of a PC or a cell phone charger, in that they produce 1,000 to 10,000 millicandles of light intensity where regular indicator LEDs may only produce a few hundred millicandles. At a distance of a foot or two, an ultrabright LED may be almost painful to look at in its narrow cone of focus.
Three are enough
A cluster of three white LEDs can provide sufficient light to enable a person to read comfortably if the light is directed in a beam. The same three LEDs can provide a diffuse illumination in a roughly 6-foot by 6-foot area in our teak-paneled (dark) saloon.
A ring of 12 LEDs makes an anchor light that is clearly visible for a mile, though the U.S. Coast Guard won't certify a homemade array. However, since we are generally cruising in waters where few vessels even have running lights and where the nocturnal boat operators are more likely to have their attention focused on the horizon than the sky, we consider our deck-level LED lighting to be more important lighting than a mast-top light. We believe, furthermore, that a mile of visibility is more than sufficient even though our boat exceeds 12 meters in length. Right or wrong, we only use the mast-top 2-mile incandescent light if we are anchored where we may be passed closely by large commercial vessels.
For those who need an LED-powered, USCG-certified anchor light or running light, Orca Green Marine makes several models. One model uses one red, one green, and three white Luxeon LEDs. By energizing the red, green, and white lights, the light shows as a tricolor running light. By energizing a pair of whites in the port and starboard sectors instead of the red and green, it shows as an all-around white anchor light. Other features that can be added to this basic unit are a strobe (the white LEDs flash) and a photo sensor that turns the light on and off.
GreenRay offers arrays that are snap-in replacements for some existing incandescent bulbs, and Stecktronics offers arrays that can be used to convert existing anchor and deck-mounted running light housings to LEDs.
All of these offerings can be obtained from Hotwire Enterprises (<http://www.svhotwire.com>). John Gambill and Libbie Ellis at Hotwire are also a good source of information on the rapidly changing field of LED lighting for marine use.
Color and energy
LEDs emit their light as electrons drop in energy. The color of light is related to the size of the drop. A red LED has about a 1.5-volt drop in energy, whereas amber has about a 1.8-volt drop, and green LEDs have about a 3.4-volt drop. Blue and blue-green LEDs (and white -- which are blue in disguise, remember) have about a 3.6-volt drop. They produce nearly their nominal light output when a current of 20 milliamps is passing through them, and these voltages are those that correspond to this current for the respective color LEDs. If greater voltage is applied, then more current will flow (and the device may overheat). Nichia-brand white LEDs can operate at a continuous current of 30 mA and 3.8 volts, but LEDs from a distributor may originate from various manufacturers and the original specifications may be unknown -- it is best to limit current to 20 mA to play it safe.
When designing a project for a boat, the normal voltage will be around 12.5 volts, but at times the lighting circuit may receive up to 14.5 volts if the batteries are being charged. Consider designing your projects for about 13 volts if you occasionally run the engine at night or maybe even 14 volts if you have a charging source at night frequently. On the other hand, if you have abundant electrical power, you probably don't need to build LED projects anyway. Plan for the LEDs to operate at 20 mA at the greatest expected voltage. We generally have had good success with this approach; even if the batteries are badly discharged and the voltage drops to 11.9 volts, the same LED circuit will give good light.
LEDs tend to have a relatively constant voltage drop within their normal range of operation. If more voltage is applied, the current rises quickly -- LEDs do not block excess current. So, if you place three white LEDs and one amber LED in series, at 12.6 volts they will pass almost exactly 20 milliamps. However, at 13.6 volts it is difficult to predict the current they will pass. The extra volt could cause the diodes to pass excessive current and overheat. It is good practice to install a resistor -- a device with a known tendency to block current -- into the circuit with the LEDs to keep the current from being excessive.
We have bought most of our LEDs from All Electronics Corp. (<http://www.allelectronics.com>) because it often has low prices, but there are many other distributors on the Internet, and local electronics shops may have a good selection as well. A few years ago, we bought an assortment of LEDs directly from one of the major manufacturers, Nichia Corporation (<http://www.nichia.com>). We have made our projects with lamp-type LEDs in a clear plastic enclosure called T-1 3/4, which is about 5 mm (a little less than 1/4 inch) in diameter and perhaps 8 mm (about 5⁄16 inch) in height. A smaller T-1 enclosure (similar shape but only 3 mm -- about 1⁄8 inch -- diameter) is also available for most LEDs. These days, we see flat surface-mount LEDs available as well. For the projects we contemplate here, the T-1 3/4 style is intended, but other case designs may also serve your needs.
Resistors: A necessary evil
Resistors have a property of blocking current known as resistance, and this property is measured in units of ohms. The voltage drop E of a resistor is equal to the product of the resistance R (in ohms) and the current I (measured in amps); this is known as Ohm's law:
E = I x R
For the example above, if we want our three white LEDs and one amber LED to only pass 20 milliamps at 13.6 volts, we should add a resistor that passes only 20 milliamps if it has a 1-volt drop (the other 12.6 volts of drop occurs in the LEDs: 3 x 3.6 + 1.8 = 12.6; see chart on Page 47). By rearranging Ohm's law, we can determine that such a resistor must have a value of
R = E/I = 1 volt/0.020 amps = 50 ohms
With a 50-ohm resistor, the LEDs are protected from excessive current at higher voltages. The resistor converts some of the power into heat, but most of the power is still going to lighting.
Resistors are a necessary evil -- necessary to prevent LEDs from being damaged by excess current and evil because they use power but do not produce light. They diminish efficiency. In fact, resistors are specific about the amount of heat they can produce. Larger-capacity resistors are physically larger. The equation for heat production in a resistor is: power W is equal to the value of the resistor in ohms times the square of the current in amps that is passing through the resistor:
W = I2R
A 100-ohm resistor passing 20 milliamps of current dissipates power
W = I2R = 100 ohms x (0.020 amps)2 = 0.04 watts. The smallest commonly available resistors are 0.25 watt, so they suffice for small lighting projects.
Sold in bulk
Resistors are sold at electronics stores and are available by mail order. In the electronics industry, resistors are sold in rolls of 1,000 for very little money, so individual resistors have a value well below $0.01. Buy them in bulk variety packs and throw away the resistors with high values (anything over 1,000 ohms) or give them to a ham radio hobbyist who will almost surely never need them either but who will still find them to be a thoughtful gift.
A resistor's resistance value in ohms is described by a color code. Resistors are painted with colored bands. The first two bands indicate the first two digits of the resistor's value. The third band indicates how many zeros follow the first two digits. The color code is 0-black, 1-brown, 2-red, 3-orange, 4-yellow, 5-green, 6-blue, 7-violet, 8-gray, and 9-white. Thus, a resistor with a value of 560 ohms would have color bands of green-5, blue-6, and brown-just one following zero, as shown in the illustration at right. A fourth band on the resistor is gold or silver to indicate the precision with which the resistor has been made. Virtually all modern resistors have a gold band indicating the actual value is within 5 percent of the color-coded value, but any resistor will work fine for an LED lighting project. The fourth band is important though. Since it is gold or silver, it is distinctive as the fourth band, so you know which way to read the color code.
Resistors are made in certain typical values. When you buy a variety pack, you will find some resistors with values close to those you have calculated you need, but probably none will be exact. Close is good enough -- even within about 20 percent of the value you calculate will probably work. (That is why the fourth, or tolerance, band is mostly irrelevant.)
Suppose we need more light and plan an array of LEDs with two each white, green, amber, and red LEDs. Now one white, green, amber, and red in series have a voltage drop of (3.6+3.4+1.8+1.5 = 10.3 volts; refer to the chart on Page 47). If we are designing for a maximum voltage of 14.5 volts and a maximum current of 20 milliamps, then our resistor needs to have a value of (14.5 - 10.3) / 0.020 = 210 ohms for each strand of four LEDs. Alternatively, one single resistor could be used to supply the two parallel strands; since this single resistor would need to carry twice as much current, it will have only half as much resistance, or about 95 ohms. In our early projects, we often followed this approach to save on resistors before we bought a larger supply, but we do not recommend it except in difficult circumstances. If one of the LED series fails, the other series will be driven by a somewhat greater than anticipated voltage. Certainly if the different strands in a circuit have different combinations of colors (and therefore differing voltage drops), give each strand its own resistor.
A couple of final comments should be made about resistors and LEDs. The first is that all LEDs look alike, and you will sometimes forget the color of a particular LED. All the LEDs are in clear cases so color is only apparent by turning them on. But you cannot simply connect one to a 12-volt source -- it will pass too much current and burn out in less than a second. A resistor should be connected to the 12-volt source, and this regulated current supply should be used to probe the LED. The resistor should have a value of about 500 or 600 ohms so it will not allow too much current to pass through even a red LED.
An exception to the issue of series resistors for LEDs is that some LEDs are sold with a resistor already built in. If you need a simple indicator lamp, a 12-volt LED may be right for you, but it is not a good choice in lighting projects because it is not very bright and cannot be connected in series to take full advantage of the available voltage.
To check an LED for color and function, connect the negative side of the 12-volt battery to one lead and connect the positive side of the battery to the 600-ohm resistor. Use the other lead of the 600-ohm resistor as the positive connection to the LED. LEDs are generally constructed with a long lead and a short lead; the long lead is positive. If the LED does not light, reverse the polarity of the connection and try again. If it still does not work, it is probably a bad LED.
There are several issues when putting the LEDs together. The LEDs must be connected with observation of the proper polarity. Since the leads of the LEDs are often cut shorter for use, it is sometimes beneficial to mark the polarity with a felt-tip pen, coloring the negative (short) lead near the point where it emerges from the plastic. Connect LEDs so that the positive lead of one LED connects to the negative lead of the LED next to it. The resistor can go on the positive or the negative side of the series of LEDs.
Use a small soldering iron (35-watt) to make connections and keep the iron in contact with the LED leads only long enough to make a connection. It is good practice to connect an alligator clip between the LEDs and the soldering point to sink excess heat, but this is often not feasible. We have not burned out any LEDs with our soldering iron, but we are always afraid we will, so we keep the soldering time as brief as possible. Of course, the average hobbyist will have no way to determine the temperature of the soldering iron, but for what it is worth, the Nichia website specifications for its LEDs indicate that the LEDs can tolerate a soldering temperature of 350° C for three seconds and that soldering should occur below the solder block in the leads.
We often have mounted the LEDs around a small piece of polyvinyl chloride piping, drilling a couple of closely spaced 1⁄16-inch holes where each LED is mounted for the leads to go through the pipe. We make the connections on the inside of the pipe, and the LEDs project outward or are bent to point in a common direction along the pipe axis. The pipe can then be used to support the entire project in a fixture.
Bending the leads is a delicate process. Hold the lead wire in two places to bend it rather than holding the LED case. Bending the lead using the case as a fulcrum can damage the clear epoxy and cause moisture to enter and create damage, or it can even cause mechanical distortion of the semiconductor and damage the junction where light is produced.
When the soldering is completed, it is important to thoroughly seal the LED leads from exposure to the environment. Liquid electrical tape, PVC glue, varnish, epoxy, or paraffin wax can be used. Coat the leads and connections to wires, and extend the coverage right to the point where the leads enter the clear plastic body of the LED. Otherwise, marine salt and moisture can cut its life to a year or less.
The easy way
LED lighting solutions are also available in prepackaged arrays that can replace nearly any bulb from various marine manufacturers at a considerable additional cost beyond the LEDs themselves -- we have seen them at boat shows. After completing one or two LED lighting projects, you may conclude that the extra cost to have a manufactured assembly is worthwhile. On the other hand, building these simple electrical circuits can be a rewarding project. Furthermore, after a moment of reflection, it easy to see that there are thousands of possible combinations of LEDs that can be operated on 12-volt systems, and your individual LED lighting needs may not match a prepackaged solution.
Several LED projects on our boat have been successful. One is a mix of colored LEDs inside a 6-inch woven basket that we hang upside down in the cockpit as a night light. The mix of LEDs includes two white and one blue LED in one series and two white, a red, and an amber LED in another series. The two series each have a 100-ohm resistor and the two are connected in parallel; the current draw is 40 milliamps.
Our unofficial anchor light has four series of three white LEDs each, for a total of 12 LEDs. They are arranged in a circle. Each group of three LEDs is in series with a 100-ohm resistor. The light draws approximately 80 milliamps.
Another project was the creation of a strand of six amber LEDs and two strands of blue and green LEDs mounted in a U-section teak molding strip over our refrigerator lids. The LEDs shine down into the refrigerator when it is opened. The total lighting strip requires 60 mA and provides enough light to prepare boat meals on the countertop when the refrigerator tops are closed.