Whilst wandering around the local Pets at Home store with my youngest last Friday, I was quite taken by the LED lights you can buy to illuminate the flow of air bubbles from the air stones used in fish tanks.

I'm like a magpie when it comes to shiny lighty things and I'm always up for some colourful chavvy LED tat. The trouble is, they wanted about ten quid for this simple submersible LED with its power supply.

Ten quid??!!

Before I had time to reach for my credit card, the cogs were already turning on how I could make my own LED bubble light for next to nothing. Sure enough, I already had all the parts I needed and construction took mere minutes - and it runs for free off my solar installation.

And here's how it works...

It's not wise to submerge any foreign objects into a fish tank unless they're made for aquatic use. You don't know how materials will react with the water or the aquatic life over time. I needed a section of tubing so I cut off a piece of the existing aquarium air line tube (it was too long anyway). I know this tube is okay as it's made to be submerged with the fishes. I threaded some two core cable through the tube and soldered it to a high intensity green LED. The LED requires 3V and I'm using a 5V source so a 100 Ohm resistor was soldered in series with the LED. Hot melt glue was applied to the soldered connections to prevent them touching and shorting out if the tube was squeezed or twisted.


The piccie above shows the LED poking out the end of the tube with a pound coin shown for size comparison. The tube diameter is about 1mm narrower than the LED so although the LED casing protrudes from the end of the tube, the tube expands tightly around the base of the LED forming a watertight seal so that only the plastic body of the LED comes into contact with the water. I know it's watertight because I submerged the LED end of the tube in water and sucked through the other end of the tube. Despite the fact that my work colleague, Sanjay the stingy contractor, constantly tells me I suck professionally, I wasn't able to slurp any water past the LED and up the tube. Just to make sure, I used a heat gun on the end of the tube encouraging it to shrink to fit further.

You can also see the 100 Ohm resistor through the tube in the above picture.

The LED is a 3V high intensity green fella originally purchased in the late Nineties as part of a home made lighting project. Said project was scrapped in 2002 when we moved house but I saved the LEDs for reuse. I could have used other colours or even one of those tri-element colour changing fancy ones with the built in binary counter that cycles the light output, but I felt the green was appropriate for this project.

Obviously, the LED, once submerged, needs to point upwards so it illuminates the bubbles as they leave the air stone. A strip of lead plant weight was perfect for holding a kink in the tube as below.

LED with tube bend

All I then had to do was submerge the thing and hook the cable up to the 5V distribution from my solar installation for free 24-hour power. The LED tube runs parallel to the air line with the two tethered together using lead plant weights. The LED sits next to the air stone pointing upwards and illuminating the rising bubble stream. It's quite hard to get a decent snap of moving coloured bubbles with my cheap digital camera so the first picture below shows what the bubble stream looks like while second picture gives a better indication of the actual bubble colour.


Bubbles 1

The above picture was taken with a flash hence the clarity but lack of colour to the bubbles. The piccie below, while not in focus because of the lack of a flash, shows the actual colour and intensity of the LED.

Bubbles 2

It's a real pleasing electric green and even with the aquarium fluorescent light on it has a high visibility.

My tenner is safe and... uh... hopefully so are the fish!

Like this? See also my Baby Biorb coldwater tank moonlight!