11th February 2018 4th February 2018 By Bzzz In lighting 5vel foilelectroluminescentfftfrequencypottingpower brickpower consumptionspectrumusb

DC5V USB PORT 10X10CM El panel Electroluminescent BackLight panel el foil el paper el sheet Led Board Display with Inverter (WHL #35)

Here’s another random thing from a colleague: A small Electroluminescent panel!

I was asked for an area lighting thingy that is slightly flexible. So unless one wants to bend the stiff backing of a mobile phone backlight unit, EL foil seems to be the solution. I’m not sure if that fits his needs, but I’m confident he’ll tell me if it’s not I bought this thing quite recently on AliExpress (mid-January 2018) for 5.22€ including shipping. Yes, shipping cost have increased by a bit, but shipping times have improved as well. Not a show stopper for China shopping as many have predicted.

As I’m unfamiliar with these panels, I chose to go for an ready-to-go solution instead of buying panel and inverter separately. Surprisingly, the market for such things is extremely limited and I only was able to choose size, because basically nobody sells that stuff. Well, I went for the 10cm x 10cm panel, as cutting down seems to work for these EL foils (reducing life span because of a sealing problem; oxygen will slowly deteriorate the electroluminescent paint), but just slapping on another square in a seamless fashion might be problematic

Panel and inverter can be separated, which should be quite useful when mounting. I guess the connectors are just barely doing the job in terms of voltage rating (I’ll discuss that later), but they are designed so that it’s quite difficult to probe and nearly impossible to touch any life wire. So that’s god.

Front (illuminated) side is pink all around, backside of the panel is pretty boring, just a brownish coating and two visible electrodes. I assume cutting is possible if you just leave the copper strips alone. As this panel is really thin, you might short out both layers when cutting them. People say you can burn it free by just applying enough current, but I didn’t test it, it’s not mine…and burning away copper is certainly more difficult than removing some conductive paint at the edges.

The inverter unit is fully potted and both cables are fixed. The input is a standard USB cable, and it does in fact use 5V. The case has two smallish mounting holes which is a nice touch; I’d wish for a more flattened casing instead of the blocky one that is used. Anyway, size isn’t that huge, so it should fit basically everywhere.

About the high voltage connectors once again: “CNDZ” doesn’t really yield much on google, so I assume these are no-name knock-off connectors. Pin spacing: Well…I measured the voltage under load, and it is 108V RMS (AN8008 multimeter) to 113V RMS (DS1054Z oscilloscope), at 304Vpp. I wouldn’t use that pin spacing for a commercial product, but hey…

The inverter does survive loadless operation. I’m not sure if it does that for indefinite amounts of time, but for testing, it did the job. There’s also no arcing

Some more shots from the Rigol: Frequency used is 1.6kHz, which unfortunately is clearly audible. It slightly changes when you touch the panel, which should alter the current consumption and therefore requires the power supply to throw in additional electrons at a different rate. I’ve also measured power consumption with the USB power meter (WHL #17), which clocks in at around 0.35A / 1.8W. So that’s 180W per square meter of illumination area. I wish I could measure absolute light output to calculate conversion efficiency, but I’m doing this at home, not in a proper lab

The driving AC is roughly sinusoidal, but you can clearly see harmonics in the FFT app on my phone:

Well, this can be quite annoying if the power supply brick is in audible distance our mounted to something that actually amplifies this buzzing noise. As the brick is potted, there’s no way to change something on the inside…

Anyway, now to the part that f*cks me over a bit, as I cannot set white balance properly. You might have noticed that in the first few photos where photos with the panel cannot be corrected, but those with the power supply can…well, having a self-illuminated surface doesn’t really help at all. So here’s the panel without correction as seen by my Canon camera:

That doesn’t really reflect the true color, so how about a comparison with the Samsung Galaxy S5 OLED screen that has a very nice white point?

It looks pretty blue, but it’s actually not far off the OLED white. It’s however significantly darker; the Samsung does run on full brightness here, so no auto-dimming and brightness on max. The interwebs claims that this means 700 cd/m², which really is blinding at night. The EL panel however has a very pleasant brightness level, which is also necessary because it is not adjustable. Well, unless you solder in some resistors to drop the voltage a bit…

Two more shots of the panel alone, the bottom one does fit the real-world color best. Note how the illuminated area has some structure to it, this is not JPEG artifacts or caused by anything further down the processing pipeline. It is visible on the panel itself and does not move with viewing angle. It’s quite different to an evenly lit LCD or OLED panel, but I wouldn’t say it looks cheap for that reason – it’s just a different way of area illumination.

And of course I had a look at the spectrum of the panel. Obviously there’s a lot of blue, but there’s also a strong, wide green band that covers a lot of spectral bandwidth down to turquoise, and a smaller reddish one. It almost completely lacks bright green to yellow colors, and a lot of the low frequency red stuff. So no wonder the camera does have some difficulties in estimating the white point, but to the eye, it does look reasonably white. I still wouldn’t use that as a working light where CRI is even slightly of importance – but if you just need a small, flexible light source somewhere, why not?