The confusion takes root in the fact that all low voltage LED lighting products are not made equal. There is a multitude of sources for LED lights on the market, very little honest technical information is available on them and the price range is extremely wide. The abundance of products and the lack of precise information has incited us to write this article. This document is based on information that comes directly from the engineers and manufacturer of our product line and is complemented by our own experience with LED Lighting in the Marine Environment.
This article will try to spare you the physics custom neon signs behind the product while giving you enough information to carefully choose what product you should install on your vessel. I apologize to all the engineers who will not find this document complete and precise, but the objective is only to provide our fellow sailors with the basic knowledge necessary to make a smart decision when purchasing LEDs for their boat.
All LED’s are semiconductor diodes. They create their light at the junction of their positive and negative sides. When power is applied to an LED, the electrons jump from one side to the other releasing light in the form of photons in the process. Different types of semiconductors produce different wavelengths and consequently produce different light colors. The warm white lights that we prefer in yachts is produced by Indium Gallium Nitride (InGaN). Add other materials, like phosphors and you get a pleasing incandescent light color.
Now, what happens when we apply voltage to this semiconductor is what we really need to look at. Apply the right voltage – in our application 12V – and the right amount of current will travel through the semiconductor and we get a beautiful, energy-efficient, bright light that will glow for thousands of hours. But, we need the right voltage, precisely 12V.
Why is that? Simple! When the generator, alternator or inverter kicks in, we often see the voltage reaching upwards of 15V or higher. The higher the voltage, the more current goes through the semiconductor, the more electrons jump from one side to the other, the more light is generated and more HEAT is generated. And, guess what is the enemy number one of LEDs? HEAT! We need to either control the heat produced or dissipate it. Apply a lot of current to an LED and you will get a very bright light for a very short period of time. Apply to little and you get a dim, useless light. That’s what happened to you friends’ LEDs.
Most inexpensive 12V LED cluster bulbs being sold today use a ballast resistor which bleeds off energy to limit the current. This ballast resistor limits current according to a simple formula: Voltage/Resistance = Current. In that world, one can reach the right amount of current for an LED by using a ballast of the right resistance for the Voltage provided. Problem is, on a boat, the voltage is not always the same, it fluctuates. Consequently, the resistance being fixed, when the voltage drops, the current drops, and vice-versa. Conclusion: low voltage = dim light and high voltage = fried LED!
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” 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.