Nothing new here folks, I've been shoving LED's into aquariums before. You might say I have 'previous' which I like 'cos it makes me sound dangerous and cool (although the knitted jumper and polyester slacks I'm wearing prove otherwise). Whether illuminating a bubble flow, lighting up a Biorb with an ethereal glow or decorating my 190L Juwel aquarium with spotlights, the aim of the game is giving my fishes a spot of colour after dusk has turned into dark and the main tank lights have switched off.

The spotlights I used when I set up my Juwel tank two years ago were off-the-shelf things that cost the best part of ten quid each. A timer was employed to switch 'em on before the main tank lights extinguished and to switch 'em off after the main lights came on the following afternoon. They suckered onto the glass above the water line and with the main lights off they illuminated different parts of the tank giving life and colour where otherwise there would be a murky gloom.

P1010009The aquarium as new in 2009 when the spotlights were colourful and before everything got covered in fish poo and algae

Earlier this year I decided to add a bit of extra vajazzle so I purchased another two of these spotlights, this time in green. Upon connecting them up I found the new green lights to be super bright and I realised it was because my two year old blue and red fella's appeared to be half burned out. I hadn't noticed how dark the old lights had got until I had something to compare them to. This annoys me as LED's should last years and not fail to half brightness so quickly.

I decided therefore to build my own moonlight effect rather than throwing more money at any more overpriced spotlights. In essence, I'm gonna make a single big bulb comprising of 16 high brightness LED's. Hey, here it is:


Looks shit doesn't it? That's because originally it consisted of twelve neatly laid out LED's arranged in three groups of four connected in series allowing them to run off a 12V AC supply recycled from a long dead telephone answering machine. When I tested it however, I found it wasn't bright enough so I squeezed another four series connected LED's onto the stripboard in a not-so-neat layout. That leaves me with a rather odd configuration but gave me the brightness I wanted. The two 10mm LED's are white and came off an old garden solar light while all the 5mm LEDs are bright blue. When mixed together the colour works out nicer than straight blue. All the blue LED's stand a few milimetres off the board allowing them to be individually angled for the best spread of light and a couple of the outer ones are pointing towards the bubble flows at either side of the tank. A couple of 1.5 Ohm resistors are being used as links and can be ignored, and the green thing at the bottom left corner is a fuse. The schematic is as below.


The circuit has been arranged so that the AC input illuminates eight LEDs with each half cycle. A 1N4001 diode on each half of the circuit (D1 and D2) clips the AC to provide half wave recification to drive the LED's. Probably not really necessary as the LED's are themselves diodes but... well... meh.


This means the LED's are not continually illuminated but are pulsing on and off at 50Hz which should be more energy efficient and prolong their life. In effect, only eight LEDs are being fully powered at any one time. If we hook a two channel oscilloscope to LED 1 and LED 16 which are on different halves of the circuit, we can see they are being driven 180 degrees out of phase ih respect to each other.


The scope was set to 5ms/div so a complete on/off cycle takes 20ms which is what you'd expect from a 50Hz AC source. Each LED is therefore powered and illuminated for 10ms before being switched off for 10ms. This works out to 50 flashes/second (duh!) which is just on the peripheral of human vision (i.e. the illumination appears constant although you might catch the flicker through the corner of your eye).

So I had my circuit, what I needed next was a waterproof container to house the thing. This Addis 200ml pot bought for about a quid from Wilkinsons while on a shopping trip with Bolton Dan (bald server man) should do the trick.


The clear base of the container is perfect for my LED's to shine through. A hole was drilled into the side of the container and a length of 5mm air hose fed through and sealed. The low voltage AC wire fed through this tube and into the container. In theory the whole thing should be pretty watertight however I don't plan to plop it into the water, instead I will be suspending it from the rear lid of the tank. Here is the rear lid with recessed handle before I permanently ruined it...


... by drilling a twatting great hole through it with a hole saw. The diameter of the hole is such that the pot can sit in it from above without falling through....


... like this. Doesn't actually look too out of place and with the air hose containing the wire hidden on the inside of the lid the installation up top is quite neat even if it does kinda look like what it is - a plastic glowing lunch soup pot suspended through the lid of a big frikkin' fish tank.


The board is angled within the pot so that the light shines towards the lower front of the tank.


It's hard to get a decent picture when you don't have the slightest aptitude or patience for photography and you're only armed with a mobile phone camera, but the snap below gives an idea of the kind of blue/white glow that now bathes the tank between 22:30 and 15:00 when the main lights are off.


The effect is more spectacular in the flesh as the light shines through the filter output as it ripples the water surface casting beams and shadows down into the very depths of Davy Jones' locker.

With my home made solution, I can add or change LEDs in the future should I ever want to change the colour or alter the brightness. Oh, and the fish love it! ...for all I know.