Technical Detail

(See also Technical Summary page.)

WHY BOTHER WITH EFFICIENT LIGHTING? MY LIGHTS WORK JUST FINE.

The "how" part of energy efficient lighting technology is inextricably tied in with the "why". "Why" is a good place to start when thinking about "how", so let us start right off by trying to answer 'The Big One'; WHY would anybody in their right mind spend 150 bucks or more for a dang LIGHT BULB? Does it make sense?

If you are buying light bulbs for your house that is connected to cheaply supplied electricity, spending that much money for a light bulb would not be cost effective.

OK, MY LIGHTS USE MORE POWER, SO WHAT?

But they don't use just little bit more power than energy efficient lighting ... they use an AWFUL LOT more! If you are a boater who seldom ventures away from the dock for more than a day or two, or one who has a large electrical generation capacity, and will always be where repair facilities for that are available, then you might not want to put money in anything that can drastically lower your electrical energy consumption.

But, if electricity must be supplied by a generator and there is a need to limit generator run time (or a desire to be able to do without it if need be) or you just want to extend time between refueling, or the main electrical energy source is alternative energy generation devices such as wind or solar power, or maybe you just do not want to lug around half a ton of batteries, then it might well make a lot of sense to conserve power. The real world result could be significantly more electricity available for other things besides lights.

Just as an example, (I will get into way more details later on), our FirstStar MKIII anchor light, while often the most visible light in an anchorage, will use less than 1/25th the power while on as that of a 'normal' anchor light bulb in the same fixture in a 12 hour time frame. This comes to an energy savings of over 25 Amp Hours in one night ... and with its built in day sensor you don't have to remember to get up at daybreak turn the FirstStar off to conserve power or make sure that you turn it back on at sunset, a decided advantage for a boat left on the hook for an extended period with no one aboard. 25 AH is enough to run a very efficient freezer for almost two days in hot weather, or a good size bilge pump for eight hours! How would YOU rather spend the electricity?

THE REALITY OF TRADITIONAL BOAT LIGHTING

It is a fact that many cruising boats engage in the very dangerous practice of running without any navigation lights at night, at least some if not most of the time, as discussed in a recent (June 2004) article in Sail magazine.

Also, any of us who have been 'on the hook' for any time beyond a week or two can attest that running a normal anchor light eats up a lot of our daily electricity quota ... juice we could use to chill the booze, call home, watch a movie, plan a route, take a shower ... or pump the bilge! That is one reason many boats in anchorage all over the world either show no anchor light or use some type of light that is designed to save electricity. However, most of these 'low power' anchor lights are also 'low light' anchor lights! You could, as some still do, use a kerosene anchor light ... I used one on my boat for many, many years ... but cleaning and refueling it almost every day, and not having the visibility of a powerful electric light is a disadvantage.

Then there are the cabin lights ... a MAJOR energy drain. Fluorescent lights can be a good alternative to incandescents as they are more efficient, but most have color quality and operating lifetime issues. The better fluorescents are also quite costly, while still having some reliability issues. Again, kerosene can do it, but with lots of drawbacks! The reality is that many cruisers live with dim or poorly lit living areas once the sun goes down most of the time ... or settle for 'pools' of light throughout an otherwise dark cabin.

NO, NO, MY LIGHTS DON'T USE THAT MUCH POWER

You may wonder how much power lighting can really use, maybe you think it can't be all that much. Perhaps I am just 'spinning' things or 'hyping' my point of view, right? Nope, research shows that the average cruising boat (not tied up at the marina, of course) in a normal 24 hour day will use as much as a bit over 30 percent of its available electricity stored in its batteries for lighting. (Smaller boats use a larger percentage, larger ones a smaller percentage). Old fashioned light bulbs convert only about 3 percent of the applied power into light, so if a newer one comes along and is TWICE as efficient, it still is only converting 6 percent of the power into light ... traditional lighting is VERY HUNGRY for your boats battery power!, while giving off only a little light and lots of heat. Even the newer incandescents, while giving more light per watt than older types, still really eat up the juice, and they get REALLY hot!

Put another way, for a boat with just one normal anchor light on all night and four normal cabin lights on for four hours a night, if you have an alternator or generator that can supply sixty amps to charge the batteries (and if they can absorb all the sixty amps!), it will need to run about one and one half hours every day to fill the need. Or, you would need as many as four large solar panels, at 300 dollars per panel! But, maybe you are energy frugal ... OK, so lets say you replace the power hungry 25 watt anchor light and running light bulbs with ten watt bulbs, and only run energy efficient lights in the cabin ... that can still run up an energy deficit of 35 AH per 24 hours, almost half the capacity that would be available in a normal deep cycle battery, or two large solar panels worth of need ... and if you have a few cloudy windless days, your house bank will be deeply discharged and maybe damaged.

Another advantage of using devices that conserve power is that your electrical supply system will also see an effective gain from the low power discharge due to the fundamental physics of the way a battery discharges under heavier load as compared to the way it will under a light load.

With the heavy load, the internal resistance of the battery goes up quickly as the chemicals inside the cells are converted and electricity is supplied. This high internal resistance will dissipate more power as the battery provides electricity to the load(s). This also applies when the battery is re-charged, that is when the battery is deeply discharged and you want to charge it fast there is a higher resistance due to a higher current flow.(See Peukerts equation for the math formula for this effect.)

With a light load the internal battery resistance doesn't change that much, so less power is dissipated as heat in the battery.

What this means is that a low power and efficient device saves power in two ways, first by being more efficient in and of itself, and second by causing the battery(s) to operate more efficiently.

BUT I HAVE A GENERATOR

So, you say, I will just get an engine driven generator. Sure, they are nice ... but need fuel all the time, are noisy, (a silent anchorage is so nice, I will even go so far as to stop the wind genny!) need their own space, and always mange to 'go south' at the worst times. And you will need to run it quite often, at least an hour or two every day if no attempt is made to conserve electricity. The engine driven generator approach can lead to over- reliance of a cruising boat on machinery which will inevitably fail, sooner or later. However, the use of energy efficient navigation and cabin lighting can help mitigate a loss of generation capacity and allow a less forced choice of a repair facility.

ELECTRICITY ON A BOAT IS COSTLY

No matter how you look at it, ELECTRICITY ON A BOAT IS EXPENSIVE!, expensive to buy the equipment to make it, expensive to maintain that equipment in both time and money, and expensive to store in batteries. The less of it you need to use while not connected to the grid, the better off you will be. Often it is more cost effective to conserve electrical power than it is to produce it! (The FirstStar anchor light can in effect replace a solar panel worth 300 U.S. dollars, for example). Light emitting diode technology is a way "how" to make some serious energy conservation happen on boats.

If you are a cruiser/live aboard boater who is willing to resign yourself to the power hungry or dim existence of traditional lighting, or you just go to bed when the sun goes down, and you are sure that keeping your boat visible to others at night will never be a significant energy drain on your 'house bank', then you may not need energy efficient lighting. But, if you want to be assured of having a visible, safe, cheerful, well lit and cozy boat without ever straining your electrical resources ... read on and discover LEDs!

ON TO THE 'HOW' OF LEDs

WHAT ARE LEDs?

Conserving electricity while giving superior lighting performance. That is where light emitting diodes come in. They offer an alternative solution to the antique lightning technology that most boats come equipped with, one that can be vastly more energy efficient while also offering improved performance and reliability over the 'traditional' boat lighting systems. In fact, properly used, LEDs can almost eliminate lighting as a significant energy drain on a boat cruising or at anchor. Modern high power LEDs are suitable for use both as navigation lights and as cabin lights, not only 'task' lights like a bunk or reading light, but also more powerful general area illumination lights.

So, what is a Light Emitting Diode(LED) and why is it so doggone efficient? The LED is a 'solid state' electronic device, meaning it is a device that has in its functioning areas a crystalline structure composed of a very pure substance carefully mixed with selected impurities or 'doped' to control its electrical characteristics. It is almost like a normal electrical diode in a circuit(remember that a diode acts like a one way check valve for electricity), and is 'first cousin' to a transistor. Like a normal diode, LEDs only conduct electricity in one direction, but what an LED does that is unique is that when the proper electrical voltage potential and polarity is applied to it, it emits light very efficiently.

By the way, it is commonly assumed that LEDs are a 'modern' invention, but the phenomenon of a crystalline junction emitting light when electricity is applied (a crystal with wires touching its surface in this case) was first reported in a scientific publication almost 100 years ago, in February of 1907! The American space program used them in what was one of the very first 'high profile' applications of LEDs, as rugged indicators designed to operate indefinitely on some of the very first satellites placed in orbit ('high profile' ... <grin>). Digital watches came later!

HOW DO LEDs WORK?

This is a 'stripped down' version of what happens, but useful. Leds emit light when electrical power is applied because in the material, there is a boundary zone between two joined crystals of slightly different types. One crystal is just a bit more conductive to electrons than the other one due to the way the two crystals are selectively 'doped' with additives, and so there is a natural voltage difference between them. When they are joined together, at their junction an electrical potential difference naturally develops. Any electricity that flows through the device must cross this junction. If the current flow is from a side that has more 'charge carriers' to one that has less, the 'voltage hump' will be increased, kinda like increasing the size of the hump in a carpet when you push on it. If the current flow is such that it will increase the 'hump', very little current will flow, and the device is said to be 'reversed biased', so like a normal diode will 'close' in this direction. If the current goes in the other direction, the current flow will not increase the 'voltage hump', and so the device will conduct and is said to be 'forward biased'. When the LED is forward biased the electron flow (current) has to achieve enough voltage to overcome the 'voltage hump' at the junction of the two slightly dissimilar crystals inside the LED. When the electrons in the current flow do that, they jump from one side to the other. As the current crosses over and gets to the other side the electrons try to be re-absorbed into the crystal on that side, but now they have some extra energy ... energy they needed to make the jump, but now no longer need. They have to get rid of this 'extra energy' so that they can be re-absorbed into the crystal, and so they 'dump' the extra energy out in the form of light.

WHAT MAKES THE COLOR?

The light is all pretty much the same color from any particular LED (except for white ... more on that in a moment) because all the electricity had to make the same jump. So the light from a red, green, etc. LED is not due to filters (although some LEDs do filter to further sharpen the color) but just comes out that way. Because the area that emits the light is very tiny, and is surrounded by reflective surfaces, the light emitted also all comes out in a very directional manner, unlike other light sources which emit light all over. Because the LED is so efficient, (many times as efficient as a 'normal' light bulb, with further gains all the time) it doesn't turn neart emits the light is very tiny, and is surrounded by reflective surfaces, the light emitted also all comes out in a very directional manner, unlike other light sources which emit light all over. Because the Le LED is so efficient, t emits the light is very tiny, and is surrounded by reflective surfaces, the light emitted also all comes out in a very directional manner, unlike other light sources which emit light all over. Because the LED is so efficient, (many times as efficient as a 'normal' light bulb, with further gains all the time) it doesn't turn nearly as much of the power it uses into heat. Also, because there is no white hot filament or other glowing hot parts to degrade, the LED will potentially last much longer than other light sources. The fact that the LED puts all its energy into making prety much just one color of light can result in a dramatic boost in efficiency just for that reason alone when compared to traditional light sources which can throw away up to 80 percent of the light by using filters to produce a particular color.

WHITE LEDS

White LEDs are a a very special type of LED. Until less than a decade ago they were impossible to make, because there was no good blue LED available, and blue was needed to mix with other colors to make white. Blue light requires the highest 'voltage hump' in the LED's crystal, and when people tried to make an LED like that, either the higher voltage caused the crystal to short out inside, or because the materials were so different on each side of the junction, stresses developed that made the junction fail. But then an unknown researcher working for an obscure Japanese company (Nichia) built on work researchers in the United States had abandoned thirty years before, and with a lot of hard work and skill and some brilliant insights into what was needed in the manufacturing process, he created the worlds first viable bright and long lasting blue LED. His work also made it possible to manufacture LEDs of many colors that are much more powerful, thus setting the stage for the current LED revolution. Now you can even get UV LEDs!

White LEDs fall into several categories, depending on how the 'white light' is achieved. By far the most common is the 'phosphor down-convert' method, where the light starts out blue in color from the crystal junction, but some of it is absorbed and re-emitted by phosphor within the LED's epoxy encapsulation/optics package so that the various colors re-emitted mix with the blue and form white. Until recently, it was very difficult to get anything other than a very white color, which was a dis-advantage for most cabin light uses, as it was considered by most as being 'too harsh', but now there are some that are very pleasing and look just like 'natural' light.

The other methods of producing white light LEDs are to mix the light from several LEDs, or to change the LED's color spectrum by other methods ... these are far less common approaches and not as well developed yet.

There are many different kinds of LEDs to select from, depending on the intended application. They range from indicator LEDs that use only a few thousandths of a watt to the 'monster trucks' of the LED world where just one can make a pretty formidable small spotlight while consuming what is for an LED the huge amount of five watts of electricity!

How can these LEDs be best used for boat lighting? Well ...

LED LIGHT DESIGN 101

IT'S ALL ABOUT APPLICATION

With Real Estate it is 'location, location, location'. With LEDs, it is 'application, application, application'. The trick is to design the light to best match the application to an LED (or the LED to an application).

GENERAL LED LIGHTING APPLICATIONS FOR BOATS

With boats, this breaks down to two general areas, first, signaling or marking lights where visibility over a given range for a given color sector or sectors is the important thing, and then illumination lighting, where the lighting is used to see other things, not the light source itself.

NAVIGATION LIGHTS

The first category encompasses the navigation lights. These must not only be visible to the required distance, they must also be very weather resistant and be able to operate without fail in the boats often harsh electrical environment, swallowing any and all abuse. Of course, efficiency is also paramount.

CABIN LIGHTS AND OTHERS

The second is all the interior lights, task and general area, as well as courtesy lights, night vision lighting, cockpit lights, and sundry other lights such as ladder and windex lights. Here, efficiency may or may not be as critical, depending upon how the light is used. Reliability is still an issue, but not as much, but there are other factors such as color quality and evenness of light pattern distribution that must be considered. Also, these lights generally will have many more control functions, such as various color selections, dimming, aiming, etc.

Now that the applications are broadly defined, we need to decide what LEDs to use and how to best use them.

LED TYPES

There are basically two most commonly used types of LEDs. First is the 'lamp' style that looks like a small domed cylinder of various sizes from 2mm in diameter to 10mm, with two wire legs sticking out of the bottom, and secondly is the 'surface mount' type that have no wire leads and mount directly to a flat surface, such as a circuit board. The surface mount types can can be smaller than a grain of salt or about as big around as a nickle.

LAMP STYLE

In general, the lamp style throws a more tightly focused beam, but the beam has less area coverage due to this. These LEDs can be aimed to take advantage of this directivness, essentially putting light only where it is needed.

SURFACE MOUNT DEVICE (SMD)

The surface mount type often has a less tightly focused beam, or that is it puts its light into a broader emission pattern. This is good if the pattern happens to match the needs of a specific application, such as a very wide angle beam used for a general area light, but would be wasteful if used in other applications. Another thing about the surface mount type, some are able to couple heat out of the LED better than the lamp style ... 'WOAH', you say, 'he said LEDs don't make heat' ... no, I didn't, I said they make a lot LESS heat, but with the more powerful models available today, the heat generated directly and indirectly (light re-absorbtion) is such that thermal issues are now critical to any successful design using these powerful LEDs. The big surface mount LEDs are also generally more efficient.

So for applications that require a good deal of directivity, such as navigation lights that require certain sectors be covered by a particular color, the lamp style is easier to use, and also for applications such as task lighting, but for other uses involving broad areas of lighting such as supplying light for the main saloon at dinner, the big surface mount type can't be beat.

Now that we have some of the general stuff, we need to look at a few specifics.

LED OPERATING CHARACTERISTICS

Some more LED/electrical pertinent details; LEDs are a 'current driven' device ... what this means is that once the correct voltage is reached so that the electricity can cross the crystal boundaries in the LED as discussed before, a very small increase in voltage will lead to a very large increase in the amount of electricity passing through the LED, and the amount of light (and heat) the LED generates. A change of less than 10 percent in applied voltage from a normal amount can lead to the LED shorting out inside or getting so hot inside it melts! You can't just hook an LED up to your 12 volt battery ... most need between 1.8 VDC to 3.8 VDC maximum applied voltage to operate properly depending on the LED. Higher frequency colors such as blue need more voltage than lower frequency colors such as red ... it takes a bigger voltage hump inside the LED (known as 'bandgap voltage') to yield more energy for the bluer colors. So the LED needs a very specific voltage range depending on the emitted color and type of LED to cause the correct amount of current flow needed to operate properly.

POWER TO THE LED

This brings us to a very important area of our LED light design, that of how to supply power to the LED. There are many ways to do this, but which type of design is used to supply power to the LED depends on many things, including what will supply power to the system, what voltage will be supplied, what the environmental conditions, both physical and electrical, will be, what level of efficiency is desired, how much the LED's light output may be allowed to vary, how compact the power supply must be, and how much the power supply will cost. These LED array power supplies are called LED 'drivers', and the selection of the proper driver is very important to how well the system will meet the design goals.

LED 'DRIVERS'

SIMPLE RESISTOR

In the 'old days', when LEDs were not very bright, and were used mostly as indicator lights such as on TV sets etc., all that was needed to use them was to put a resistor in series with the LED to cause the LED to pull enough current to light up, but not to pull too much current. This resulted in the LED getting its correct current at nominal supply voltages. The LED would drop only the voltage needed to 'drive' its current, while the resistor dropped (dissipated) the majority of the voltage/power. This worked, after a fashion ... with a resistor, if you made the LED draw sufficient current at low normal voltages so that the LED was fairly bright, then the LED would tend to draw too much power at high normal voltages and fail prematurely.

With the newer LEDs putting a premium on brightness, there was a need to run them at full power as much as possible, both because this made the most of their electrical/optical potential, and because each high power LED was expensive.

With simple current limiting resistor designs the resistor must be selected to limit current to safe levels at normal high voltages. The result was LEDs that were safe, but dim. We don't want dim, but do want safe ... so the current limiting resistor method of supplying power to 'drive' the LED is obsolete for the most part for these applications.

LINEAR ... STILL RESISTIVE

There are various other approaches to satisfying the LED's need for current control. One of the most common now used is something called a linear regulator. This is basically just a fancy transistorised variable resistor with sensing and feedback, in a neat little package on a heat sink. The heat sink is needed, because although this device does do a much better job of regulating the power to the LEDs than the simple passive resistor in our first example, it still does that by wasting any power that is at a voltage above what the LED needs by turning it into heat. So at best, it is less than 70 percent efficient, often only about 50 percent. When we want the benefits of LEDs, that is top efficiency and no waste, it is not so good to couple our efficient, cool, and expensive LEDs to a cheap, hot and wasteful power source, right?

SWITCH MODE ... VERY EFFICIENT

Well, there are other options ... there is something called a DC-DC switch mode power converter. It posess even better power regulation than the linear type. It takes the incoming power and converts it into the correct voltage needed at the output while supplying the needed current ... and it does that very efficiently, sometimes in the mid 90's percent wise. It does this by chopping the power up into tiny 'bursts', then converting some of the voltage in these bursts into current or some of the current into voltage by transforming some magnetic field energy into electric field energy or the other way around, and at the same time re-assembling the newly converted 'bursts' into steady DC. It is 'smart', too ... it senses what its output is and compares that to what is needed (or what is is set for) and adjusts itself to give that. Sounds complicated, but it really isn't so bad.

The upshot is that very little power is wasted. This type of design also operates over a very wide input voltage range, usually wider than any of the other designs. The main disadvantage of this type is is its size, complexity, and expense. In reality, the extra complexity does not create a reliability issue, instead with proper design the improved performance increases overall reliability. However, size and cost are issues ... but this type of 'LED driver' is fast gaining the upper hand, because the newer higher power LEDs are even much more demanding of a tightly regulated power supply, and may require other things as well that are easier to implement with this type of design. (There are also some other reasons why in some cases a DC-DC converter might be better for some LED array driver lighting applications, and I will go over those later.)

PULSE WIDTH REGULATION

There is yet another option. You can supply the LED with a pulsed power source, instead of a steady one. This could be either a source of changing polarity (AC), or one that always maintains the same polarity (DC). If you use AC, the LEDs will conduct with just one polarity, so I will consider only DC types here. An advantage of this design is that the circuit is always either all the way on, or all the way off, so no power is wasted, dissipated as heat by a component that is not in full conduction mode.

TRICKING THE MIND'S EYE

LEDs have what is called a 'fast rise time', that is that as soon as the proper voltage is reached, they begin to emit light, and they also stop emitting light equally fast. They function in this manner hundreds of times faster than a light bulb filament. It is well established that within certain parameters, the human vision system's response to a pulsed light source is not linear.  (The Broca-Sulzer effect)

This phenomenon is still not completely understood, but it seems to occur due to a sort of time delay between what the eye sees and what the eye tells the brain it saw. If the light pulse parameters are correct, the LED will turn on to a certain peak (and this effect is much more noticeable with a square shaped waveform), then the eye tells the brain the LED is on, then the LED turns off. Before the eye can decide the light is really off and tell the brain, the LED turns back on again, so as far as the brain is concerned the LED never really turned off. And so on and so one with more pulses so the light looks continuous.

By this method it is possible to trick the brain and make it think that the LED's peak 'on' time brightness is almost equal to the brightness the LED would have if it were operated continuously, on all the time, at this peak value. It was not so easy to take advantage of this 'brightness enhancement' effect until LEDs came along with their fast rise time characteristics.

Of course, it is not as ideal as this, so the amount of 'gain' is less, but it is possible to make the LED look much brighter for a given power consumption by using this technique.

EVEN INTENSITY

And there is another effect. That is, it is possible to trade off light pulse duration for intensity, so that a shorter but brighter pulse will look as bright as a longer less bright pulse. This is also due to certain neurological mechanisms in the human vision system closely related to the ones previously mentioned. (Bloch's law)

LED JUNCTION TEMPERATURE CONTROL

Also, as mentioned before, the LED is a current driven device. As the current through the LED rises, the LED's junction temperature, that is the temperature that occurs where the LEDs do most of their work, at the junction between the two dissimilar crystals, will go up. A LED can take up to a given junction temperature indefinitely, but at a certain point, the time the LED is operated at a given junction temperature must be limited. As input voltage and so current rises, this time becomes shorter and shorter. By using pulse width control, and controlling the duty cycle of the 'on' time pulse, (that is the on time percentage compared to the off time percentage) the time that the LED conducts during any given input voltage can be set so that the 'on' time never exceeds what the LED can take for a given voltage. These values are taken from the LED's data sheets and programmed into the circuit.

ALL TOGETHER EQUALS VPW DRIVER

This averaged peak-limited current/temperature regulation is combined with the parameters needed to trick the brain into making the LED look brighter and also with the parameters needed to vary the pulse width to make the arrays light output look as bright for different boat supply/LED supply voltages.

The result is a variable pulse width (VPW) LED driver design that is even more efficient than the DC-DC converter type for the amount of visibility per watt. It maintains the LEDs at a fairly even brightness level across the input voltage range while using close to the same power (Amps times Volts) across this same input range (it does not dissipate or waste power as the input voltage goes up as most drivers today will). So it generates almost no heat, is more compact and more robust electrically than the DC-DC converter type, and makes very little or no RFI or EMI. It has a gain of 60- 70% over the DC-DC converter type most of the time when used for applications involving human perception of the light source, for example when used in LED navigation lights. The 'brightness enhancement' effect is somewhat less efficient in illumination applications, but one of the advantages of the design here is the ease of implementing 'lossless dimming'.

SUITABLE DRIVER TYPE MATCHED WITH APPLICATIONS

The type of LED driver selected depends on the type of LEDs used and the end use application. For a small indicator light that draws very little average power, a resistor may work well. For a small task light that is only on occasionally, the linear type may work well. For navigation lights, either a dc-dc type or a pulse width type would be most effective. A task light that is used quite a bit could perhaps best be designed with either a pulse width or dc-dc converter type. For large cabin lights, the dc-dc converter is probably the best choice.

OTHER FUNCTIONS

There are many things the LED driver may be asked to do besides simply supply the power to the LEDs. Some other functions could include automatically shutting off a LED array during daylight hours, controllably dimming the LED's average brightness, shutting off one color group of LEDs and turning on another, shutting off one sector group array (light sector pattern for navigation lights)LEDs and/or turning on another, sensing the LED's power consumption and reacting to an abnormal condition, sensing the LED's temperature and adjusting the average power to them to a safe level for that temperature, input low or high voltage sensing with pre-programmed response, and providing various user interface control input options such as programmable control options, etc. The drivers most suitable for implementation of these other functions are those that already use a separate IC to control the LED, such as the DC-DC converter type and the pulse width type.

THE HOSTILE ENVIRONMENT OF A BOAT

A boat is actually a very hostile environment for electronics. (You knew that, right?) Besides all the physical assaults such as hot or cold temperatures, sea water sprayed or violently thrown about, possible immersion in corrosive water, blows, shock and vibration, etc., there is the electrical environment. This can be a very rough enviroment indeed. We must consider protection from over-voltages such as those due to poor or improper battery charging regulation or overly aggressive charging regimes, more serious over-voltages from malfunctioning equipment, transients from such sources as large inductive loads being suddenly released, and spikes that can be very short lived but have voltages in the hundreds of volts. Our light should be able to swallow all of this and not be bothered or damaged in any way. Not only that, but we also want to be sure that if the worst happens, say a lightning strike that fries the lights circuitry, there is a dependable fail safe fusing function so that the malfunctioning unit will not create a danger to the rest of the boat. For all of these reasons, the voltage and current protection of the light must be of the highest order.

This protection will be added to the design requirements of whatever driver type we select. Not only that, but we need to consider that the light should be able to operate in a normal manner with a wider than normal input voltage range, so that if the charging system is not working correctly, for instance an unregulated wind generator is overcharging or undercharging the house bank resulting in either significantly higher or significantly lower voltages than would be usually encountered, the light will still work correctly in a normal manner in spite of that.

APPLICATION AGAIN

We return to the application. It is the intended lighting application that informs the selection of all other design choices ... the selection of the LEDs and the form the LED array will take, as well as any included optics, the driver that will supply power to the LEDs, and the functions that the driver must control. Once the application is decided all other design considerations will follow.

But to decide on the application, it is necessary to first be familiar with the requirements, that is the need. This is partly determined by existing regulations and codes, partly by user needs and expectations, and partly by the market.

So first, we ask what are the needs and requirements in terms of any existing rules or regulations, then we see what the end user wants or expects, and last we try to design the light in a manner that will meet the market need in a cost effective and reliable manner.

In all cases, the main goal here by using LEDs as the light source is to gain an increase in electrical and optical efficiency and reliability, while meeting existing performance parameters in terms of rules and expectations relative to traditional lighting. So we want to design a light that is as bright or brighter than a normal light but one that is more reliable and efficient than a normal light. The 'extra features' will be icing on the cake.

Go to Technical Detail page 2.