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Most automotive and inexpensive LEDs are based on the ballast resistor model. They work fine in automotive because the voltage variations are smaller than those found in the marine environment and also to the fact that most LEDs in the automotive world are used for turn signals or brake lights. These signals are not on for a long period of time so heat is not a problem. One can also use a resistor that will handle 14V while maintaining an acceptable current level for the LED generate enough light. This makes automotive LEDs inexpensive, but unsuitable for the marine environment.

Now that we know that a ballast resistor is not suitable for our environment, what do we do next? Let's start with what we have learned so far. We know that a resistor is a passive device that can't maintain an even current with a changing voltage. So, what are our other options?

What if we had a type of resistor which could accommodate the changing voltage? There is such a device, and it is used by many LED cluster manufacturers. The device is called a Linear Regulator, and it is a small step up in control technology from the primitive ballast resistor. A Linear Regulator is a low-cost control method which can be thought of as a variable resistor that varies the resistance according to the load in order to provide a constant output voltage to the LEDs. Because it is still a resistive device, it controls excess energy (above that required by the LEDs) by turning it into heat. But wait a minute, isn't HEAT the great enemy of LEDs? That's right! Of course, with proper design one could dissipate some of the heat, but overall, Linear Regulator can only work for small voltage variations, which is fine for some applications, but again, not suitable for the full of battery banks, solar panels and generators and inverters of our electrically hostile marine world.

Hopefully the above makes it very clear why ballast resistor bulbs and cheap bulbs have no place on a boat. From what you have read in the previous paragraphs, you are now considerably better informed than the average person looking for LED lighting. Not only that, you are most probably better informed than most of the uninformed merchants out there selling LED bulbs to the unsuspecting boater.

So what else is available in state-of-the-art LED controls? It seems what we really need is a sort of closed-loop device that looks at the incoming voltage and maintains the constant current feeding the LEDs even as the voltage fluctuates, all of that while keeping minimum heat. And, you guessed it, the device exists! It's called a DC/DC Buck Power Converter. It is an expensive way to supply energy to LEDs, but it has all the advantages that we are looking for.

The Buck Power Converter is a complex little device, but its function is somewhat simple. To describe it in layman's terms, it basically takes an energy source and switches it on and off. During the "on" led wall light manufacturers state, the energy is stored in an inductor and during the "off" state, the inductor releases the energy to the LED. The ratio of "on" and "off" time is called the duty-cycle. For example, a 25% duty-cycle would pass to the LED only 3V from a 12V source. All we need to do is control the duty-cycle according to the input voltage and we get constant current feeding our LED. The Buck Power Converter controller does this by monitoring the current to the LEDs through a current-sense resistor and adjusts the duty cycle either up or down to correct the current in order to match the LED optimal current requirement. This way we can push the envelope on the brightness of the LEDs without worrying that the source voltage fluctuations will take us past the maximum rated current of the LED and end up with a fried LED cluster.

This looks really great, but there is one last issue to deal with before we get the brightest marine grade LED replacement bulb: the BULB itself, the packaging!

We need to package our clusters in such a way that we achieve the maximum output possible in a real small package while ensuring maximum life expectancy as well. I'm sure at this point you remember HEAT! How can we pack lots of power in a small cluster and yet not overheat the bulb?

Most interior marine lighting applications use a 10W G4 bulb, which is quite compact, so the fixtures tend to be small as well. The replacement LED cluster bulb must be very small to serve as a retrofit for the original halogen bulb. It also has to produce similar output and color to the original halogen, and still be able to dissipate heat. This ends up being quite a challenge.

There are two ways to pack lots of light in a small package, and each has its pros and cons, but both are acceptable solutions. One is to use many small lower-powered through-hole LEDs clustered together in a small package, and the other is to use just a few high-powered surface mount device (SMD) LEDs arranged on a thermally efficient support for maximum heat dissipation.

The best solution is a compromise between: Output, Heat Management and Shape. To achieve this we tweak those three parameters until we reach our goal. That's why you find so many different combinations of shape, output and support material in LED product offerings.

With a little research you will find that there are just a handful of companies manufacturing and marketing LED clusters with constant-current control that are suitable for marine use and, it is interesting that most of these companies are owned by sailors. What is really sad is that the customer base is unaware of the differences between LED products.

So how can we tell we are buying the right LEDs? Here are some basic rules:

If the provider doesn't specifically indicate that he is selling DC/DC constant-current converter products, then there is a high likelihood he is not. Anyone selling a constant-current LED product will be sure to highlight that fact, and charge accordingly. Remember, you always get what you pay for!

If the "marine" LED products are being sold by an outfit that also sells glow-in-the-dark rubber ducks, tiki lights and camping lanterns, it is likely that he has no interest in the higher-cost high quality marine products. Beware of copycats!

If the product specification is not specific on a voltage range like 8V-30V or similar, it is not a constant-current product. Again buy from someone you trust.

Look for dealers or companies that are owned by mariners. They usually know what they are talking about, they use the product.

We hope this document has provided you with valuable information and that you will enjoy bright, long-lasting and energy-efficient lighting on your boat for years to come.