I recently needed some lights for a boat, but all of the options online weren’t “efficient” enough. So I decided to take matters into my own hands and try my best to make the most efficient LED lights I could. In regards to light-bulbs, efficiency generally means how many lumens per watt the light bulb delivers, although for some specialized applications this may not be ideal due to the definition of the “lumen”. Generally, the higher this value, the better.
For comparison, here’s a little chart of the lights I found, and their respective efficiency:
|Recessed LED Puck Lights||85lm/W|
|IKEA RYET Bulbs||80lm/W|
|“off-the-grid” 24V bulb||95lm/W|
|“incredibl[y] efficient” work light||53lm/W|
|My panel light||~200lm/W|
Basically, all of the store-bought bulbs are very low efficiency. Funny enough, the bulb that advertised itself as being the highest efficiency turned out to have the lowest efficiency. I thought it would be very important to use high-efficiency lights on a boat because that would be less expensive in the long-run, compared to buying and maintaining a larger power bank.
For my design I chose some 205lm/W SMD LEDs from Samsung, along with a very simple (two transistor) linear drive IC, and a small current-set resistor. You can view the Digi-Key components here. I chose a linear driver because I felt as thought I would not need a switch-mode supply, plus I wanted to increase the durability by using less components. I could improve the efficiency with a buck converter over the operating voltage range of the battery, but since the battery generally around 11.3V, I decided to optimize for this condition.
The power supply for the boat is a 12V AGM battery, which has a voltage range from ~11v-13v. In order to take full advantage of this voltage range (and thus create a more efficient driver), I balanced out the current going to the 4 LEDs in series with their forward voltages. I ended up driving the LEDs at roughly 80mA (15mA more than the test current). According to the calculations I did, the driver circuit should be almost 100% efficient at the forward voltage of 11.3v, around 90% efficient on average the rest of the input range, and only about 80% efficient at the very peak charging voltages of 13v and above.
The PCB design was very simple and straightforward. Simply connect the driver and resistor in series with the LED string, put a few mounting holes, some connections for daisy-chaining the lights, and some identifying text.
I opted to put the driver and text on the opposite side of the LEDs, and I kept the side with the LEDs pure white for ascetics.
Since the actual PCBs are still en-route, I decided to solder a test circuit on a breadboard I had. The LEDs were really bright, and used slightly less current than I predicted. I compared with a 1.4 watt LED strip I had, and these panels were much brighter! (and used about 0.8W)
You can view the schematics, board, and tests I ran on the panel here on GitHub. I will update this post when the PCBs arrive. Since each panel gives off roughly 150 lumens, 5-10 panels should be enough to light up the deck of a boat.
The panels have arrived and been installed on the boat. Two lights in the bridge were enough to read with. Nice!