In the previous project I created a light box to display abstract art that my friend Michele gave me for my birthday. Really, I just created it for fun, but the feedback I got on it encouraged us to take it a bit more seriously, and create a few “proper” ones.

This is the first. It’s another translucent art piece from Michele Witthaus that I’ve backlit by five 40cm RGB LED strips controlled by an Arduino. The art comprises sheets of cellophane, with a sheet of white Perspex behind to spread the light evenly and a thin sheet of vinyl in front to soften the edges.

I like to use the brand name because that’s what I’ve always called it (like ‘Hoover’ for vacuum cleaners) but the generic name is acrylic. Clear acrylic is actually clearer than glass, but I used a white one made for light boxes. It spreads the light but hardly attenuates it. It was 3mm, but thinner would probably been fine. The artwork was supplied to me attached to a thin vinyl sheet – the sort you stick on windows to make them ‘private’, so without the light on the art is quite pale and vague. The vinyl sits behind it so it’s backlit by an even glow.

2018-12-05 15.59.16.jpgAs I discovered last time, if the LED strips are too close to the artwork then you can see lines of light and not-so-light. The rule of thumb is that the distance between the rows of LEDs should not be greater than the distance between the LEDs and the art. There’s a gap of just under 8cm between the rows. However, we had found a rather nice 50cm square black frame from IKEA. Unfortunately, IKEA’s idea of “deep” – as in “deep frame” – was less than half of that, so some DIY wood work was necessary. I bought some skirting board from Homebase and added it to the inside of the frame (after placing the artwork and the perspex). This extended the depth to around 8cm. I then used the original hardboard back which I screwed onto the skirting. I used hot glue to attache the LED strips to the inside of the back.

The front of the frame is the original ‘IKEA black’, whereas I painted the sides. This was actually a nightmare! First, I sprayed the sides with an all-covering black paint I had used (successfully) for the Bearing Witness project. I had to assemble the frame, complete with art (because the side extensions hold the art in place), and mask off the front and back with plastic. Unfortunately, the “all surface” feature of the black spray paint did not include IKEA frames, and it immediately started to peel off. I had to completely dismantle it and sand the paint off the sides of the frame and the extensions, and start again. This took, well, you can imagine. Then I cleaned everything, reassembled it, and this time used the proper method – primer, undercoat and two coats of black gloss paint, applied with a brush. Painting the sides of the frame and not the front was challenging (paint seems to like seeping under masking tape), but I’m very pleased with the final result. It reminds me of the mirror glazed cakes you see lately!

Don’t get me started on the price of LEDs! The thing is (too late…) if I buy a 5 metre strip of 12V (12 volt) 5050 (5mm square) RGB (3 LEDs per pixel, red, green and blue) 60/m (60 LEDs per metre) LEDs from China (e.g. on eBay, AliExpress, Amazon etc.) they cost (as at December 2018) £5.50, including postage. If I buy the same thing from a UK retailer, the price is £106 (yes, a hundred and six pounds). Now, I appreciate that the UK supplier may have better quality control, but even if half the Chinese ones were faulty (they are not) I still can’t figure out why the mammoth difference. The best (only) explanation I’ve seen is that the UK ones have thicker copper tape, meaning they run cooler and thus last much longer (heat can severely shorten the life of LEDs). This may be true, I haven’t measured it. Anyway, as a precaution I usually run them at about 70% of their maximum at most (the last 30% doesn’t make them hugely brighter), and they are usually changing colour/brightness, so individual LEDs are not on constantly.

So, I used 5 x 40cm of Chinese LED strips. At 60 LEDs/m, 20mA/LED, that’s 1.2 Amps if all the LEDs are on (three LEDs of the same colour are in series from the 12 Volts, so it’s 0.02 Amp * 3 colours / 3 in series * 60 units = 1.2 Amps) * 12 Volts = 14.4 Watts. Since 5x40cm = 2 metres, that means the maximum current required would be about 2.4 Amps (depending on various things, including the temperature of the LEDs). However, for this project I wanted the light to be of similar brightness for every colour combination. That means, for example, that White (3 LEDs) needed to be dimmed significantly so as not to be much brighter than Red (one LED). The upshot is that it never draws more than one Amp, and usually quite a bit less.

2018-12-05 22.39.37.jpgI built a small PCB by routing a small piece of blank PCB by hand using a Dremel on a stand and a router bit. It’s easier than it sounds, you just need to get the height of the PCB correct (add pieces of paper under it) then move it slowly). Then I used three surface mounted MOSFETs to switch the three colours on and off (dimming is just turning them on and off really fast). It’s the same method and electronics I used for the uplighter project.

The control circuit was similar to that project as well, except that instead of using an Arduino Nano I used a Digispark board containing an ATTiny85. These are much smaller (physically – the board is about the size of a postage stamp) and has less of everything (less memory and IO (inputs/outputs), but works pretty much the same way as the Arduino. Three of the outputs use the built-in PWM (pulse-width modulation) to fade each colour from off to full in 254 steps by switch on the transistor (on my PCB) on and off, and thus the LEDs.

I found 9 unique colour combinations that matched the acetates well enough for some of them to “disappear” when backlit by a matching colour. So, for example, if the whole piece is lit by red light then both the red and the yellow acetates let through a similar amount of the red light, whereas blue hardly lets through any, thus the edge between red and yellow acetates is no longer visible, but the blue stands out.

Originally, the software cycled through the colours, staying on each colour for 2 minutes and taking 15 seconds to fade to the next colour. As you can see, Red is almost on full (200/254) whereas white is only 135 per colour so as not to be hugely brighter:

                {200, 0, 0},        // 1  Red
                {200, 22, 0},       // 2  Orange
                {200, 110, 0},      // 3  Yellow
                {45, 200, 0},       // 4  Yellowish green
                {5, 200, 45},       // 5  Bluish green
                {0, 15, 250},       // 6  Blue
                {135, 135, 135},    // 7  White
                {190, 0, 190},      // 8  Purple
                {200, 0, 50}        // 9  Pink

The design was intended for a living room / lounge, so the slow change was to avoid drawing attention to the piece. There is also a button underneath which was to allow one colour to be permanently selected (when you pressed it it cycled through the colours, staying permanently on that colour (or cycling through the colours if the button was released when the lights were off). It stored the setting EEPROM so as to remember what to do if it were switched off and back on. This design worked rather well, and I had it in my home and used it quite often for some six months.

2018-12-06 16.43.41In December 2018 the piece was accepted for the Interact’18 Digital Art Exhibition at the LCB Depot in Leicester. I changed the software to be more appropriate for an exhibition space – where people may not stay very long. I set the ‘on’ time to be randomly between 15 and 40 seconds, the ‘fade’ time to be randomly between 5 and 15 seconds, and the ‘next colour’ to be randomly selected, and disabled the button.

2018-12-07 19.01.22.jpg
The exhibition is on now until December 21st 2018. We (Michele and I) are very pleased with how the piece looks on display at the LCB. It was not created to be exhibited, or anything other than because we could. Maybe that’s the best way to ‘do’ art.


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