Electroluminescent Material Light Sensitivity

[Drjaymz]

I bought some EL paper from eBay which comes with a cheapy EL driver, so cheap you can hear it singing away and something like 4khz.

What I didn't expect was that when I came out of my dark shed the frequency of that singing changes.  I covered it up and it goes back.  I went to my desk lamp and sure enough the freqency of the circuit changes when light falls on the EL strip.  I was not expecting that.

I haven't mangled the driver yet, but its probably a self-resonant super cheapy thing, I think it produces AC.  so just a couple of transistors and maybe a transformer or something even more crude.

I googled it and didn't find much. I would image some property of the material changes with light exposure. Its unlikely to be temperature because its instant, capacitance or resistance maybe.

[Drjaymz]

Ok, because I'm meant to be working I don't have all my kit with me, but I have got a chinese component tester.  I checked and the frequency reduces when its light.

It thinks the panel is a capacitor with an ESR of 17R.
In the Dark it thinks its 11nF
In the Light it thinks its 22nF

So its a light sensitive capacitor - thats pretty groovy, its not a slight effect either, it doubles its capacitance.

I did open the driver and its a centre tap inductor (looks like mini transformer) there are two SMD transistors and a 5pin package which might be a double fet or diode jobby, not sure its so small I cannot see a thing, but I imagine its a push pull oscilator thing.

So I didn't know that and I guess if I searched properly I'd probably find it mentioned online somewhere.

I'm going to guess there is a photodialetric effect?  Never heard of it.