underwater led light

Thread Starter

not very smart

Joined Jul 30, 2010
hello all,
i want to make lights that will attach to the underside of my boat to "light up" the water at night. i will machine aluminum "pots" to hold the LEDS & DRIVERS and use a opticlly clear casting resin to encapsulate the electronics in the "pot". sounds like i got it all figured out yeah? no i don't!!! i'm completely ignorant when it comes to anything electric. so i'm open to suggestions but heres what i've found so-far....brightest leds i found were luxeon 3 up endurstar's...i don't know how to wire them to drivers or whatever i need. i want them bright as possible. i pland on having several in each "pot" an array i guess its called.i've read some of the other posts with a lot of formulas ect. which i can't figure out....notice my user name...so i'm looking for help on a most basic level, part numbers,suppliers,wiring diagrams, ect.. all help is greatly appreciated!!!thank you in advance attached is a pic of what i'd like to do.



Joined Mar 24, 2008
I think you've come to the right place.

Have you read this? Chapters 1 and 2 are an introduction to LEDs, some of it will probably be over your head (or not), but it is a start.

LEDs, 555s, Flashers, and Light Chasers

Did you make those cases? They look very decent. They would be ideal for potting (sealing) the electronics in clear epoxy to attempt to make them water proof.

It would help if you could give us what the part numbers of the LEDs are and where you got them. This way we could look up the specifications of the parts (step one).
I've actually made an underwater LED light myself.

I used a thick piece of acrylic, which is very clear. I drilled blind holes, one for each LED, a little bigger in diameter than the LEDs. Then I filled them all with some optically clear epoxy, and then pushed an LED into each one. This epoxy was very good and filled all the holes and left no bubbles. Therefore, the front of all the LEDs looks water-clear to the surface of the acrylic.

Then I wired the LEDs with a wire-wrapping tool on their leads, and snipped off the excess lengths of the leads.

the acrylic piece was circular. I potted the whole thing into a PVC enclosure, made from the end-cap for a 4" pipe, with the wires coming out the back. I used paraffin wax to pot the whole thing into the cap, and then used RTV sealant to waterproof the acrylic to the PVC. The wax was to make the whole thing about neutrally buoyant in water. Yours is attached to a boat so it's different, but wax can still work.

Anyway, for the electronics, the simplest way is to use a current-limiting resistor. You must know the voltage of your power source, which is probably a 12V battery, so maybe figure 12V nominal and 13.5V max. Then put LEDs in series strings with as many as will fit for the forward voltage. For example, if they are 3.2 Vf then three in series. Then add a current limiting resistor on each string in series, and voila, you have regulated the string based on the supply voltage. There are plenty (maybe dozens!) of threads here about calculating LED current limiting resistors.

Otherwise, you could go with a more sophisticated LED lighting controller, but I don't know much about that.

Thread Starter

not very smart

Joined Jul 30, 2010
hello all, thanks for all your help but its still not "dummied up" for me to figure out. calculation tables and tech data is extremely usefull if only i knew what it all meant. so with more information sounds like i found the right group of people. here it goes... the cree xp-g r5 seems to be the brightest one, and if i'm reading the tech sheet right looks like i can drive them at 1500ma (whatever that is) for maximum output.i have a large battery bank on my boat (12 volt) and am not concerned with power consumption, and they will be underwater so heat should not be an issue. i was thinking of 10-15 leds per fixture. i know i'm asking alot but what i need is a materials list and a wiring diagram. (i am a metal fabricator and used to working from prints) http://www.cree.com/products/pdf/xlampxp-g.pdf
heres the link to cree tech sheet... cool white r5 thabks again. also anyone interested in building these things (wiring soldering ect.) let me know. thanks scott


Joined Jul 26, 2010
Don't forget that large LEDs such as those generate a lot of heat and need a heat sink according to the spec sheets, just water on the tops of them won't be enough because if I recall the heat comes out the rear.


Joined May 9, 2009
It's not necessarily that LEDs get very hot, but they do overheat easily. Temperatures above 65°C are known to significantly reduce their lifetime. In a sealed unit, this effect is magnified. Attaching the LEDs to the chassis of the light fitting will help with cooling but is no substitute for proper heatsinking.

Thread Starter

not very smart

Joined Jul 30, 2010
thanks for the info. i think i can address heat by machining the bottom of the "pot" to 1/8" thickness and machinig cooling fins on the rear of the unit to dissapate heat into the water.so for the electronic bit....i think i've read enough to be dangerous now. am i right that a single cree xp-g r5 (which actually has 3 leds on it) count as 1 led or does it count as three? this info is needed to calculate driver size. t think i can do 1 string of three of those cree xp-g r5 in parralell and use one buck driver 1000ma and run this from 12v directly with no other resistor. am i right????? or am i setting myself up for a meltdown??? if my scenerio is correct than i i want 12 xpg's per "pot" than i would run 4 strings of three. (i think) can't wait to here what you all have to say. thank's again scott