Tuesday, January 12, 2010

Glow-in-the-Dark sketch wall and LED pens

I've finally realised one of my childhood dreams; I'm now the proud owner of a glow-in-the-dark wall - just don't tell the landlord!

I've had some glow-in-the-dark paint knocking around for quite a while and was inspired to do something with it when I saw this post on hackaday.com - "Record player display sans POV". I thought "the kids" would have a lot of fun using LED flashlights to write on something that was phosphorescent.

To start with I just coated some stiff card with the phosphorescent paint and hacked together a simple UV-LED flashlight. The flashlight design was taken from this Instructable - "Make A Mini LED Light". I found it while trying to find ways to make my own battery holders for a more standard flashlight, but this idea was so simple and small that I decided to go with it instead. All I did was to substitute a UV LED in place of a standard one.

After making the prototype I showed it off to "'er indoors" (this may not mean much to you if you didn't grow up watching "Minder" in the U.K.). Her response was a little unexpected - "Hmmm.... why don't we paint the wall with glow-in-the-dark paint? That way loads of kids can play at once!". So that's what we did :) We isolated a good amount of wall with painters tape, we just wanted it to be slightly taller than the kids. Then we put on 2 coats of white primer, 3 coats of the glow-in-the-dark paint and a couple of layers of varnish (so the kids didn't immediately scrape off the latex based glow paint). After removing the painters tape, I was pleasantly surprised to see that the wall didn't look much different.

Unfortunately, my night time camera skills leave a lot to be desired (i.e. they're crap), so I don't have many pictures of the kids playing with the wall. I can say that they were very excited and played with it for days & were very keen to get all their friends to play too whenever they came over. At one point we had a complete sea-scape covering the whole canvas with storm clouds, jellyfish, 'normal' fish and deep sea monsters. In the picture below I'm holding one of our home made light-sabers next to the wall in an attempt to allow the camera to focus (see this filthwizardry post for more lightsaber fun- "balloon and torch lightsabers").

I think one of the favourite activities, however, was with an old SLR camera flash. Get the kids up against the wall and blind them with the flash. If they recover (ok, you could just tell them to close their eyes) they'll get to see themselves glowing in silhouette form on the wall .

Hmm... ok, maybe it was one of my favourite activities as well.

After a couple of days playing, I ended up buying some LED keychain flashlights (like these from Amazon) as I quickly ran out of parts.

Here's a few in-production pictures of the ones I made:
I made 4 to begin with. All you need is a pushbutton, a UV LED, a coin cell battery and holder (and a soldering iron + solder for connecting it all up).

Connect the positive lead of the LED to the positive battery holder connector, cut off the rest of the lead so it doesn't get in the way, then attach the pushbutton to the negative battery holder connection and the negative LED lead. That's it!

Here's the first one working (nice purple glow). Some hot glue made for good protection and electrical tape wrapped around the base of the LED helped to focus the beam.

You should probably use a resistor to protect the LED... The datasheet for my LED stated that it required 3.2V to operate and the coin cell is only rated at 3V so I decided to leave the resistor out.

Important: Bright lights/UV lights can damage your eyesight. Do not shine the lights into anyone's eyes and make sure any kids playing with these are supervised and told to shine the light only at the wall. Extra care should be used when using UV light - the human eye can not detect it (i.e. you can't see it) which makes it easier to overexpose your retina as you don't have the same pain response as with intense light in the visible spectrum.

If you're nervous about this then the standard keychain lights work pretty well. The homemade UV ones just give a longer lasting glow.