German LED Cloud Ceiling

[Ken_McE]

At the Fraunhofer-Institut für Arbeitswirtschaft und Organisation (IAO) in Stuttgart, low rez LED clouds drift across the office:

http://www.theregister.co.uk/2012/01...cloud_ceiling/

[StarHalo]

Pretty badass, that puts the plain cyan SAD/health lights to shame..

[pretmetled]

Indeed pretty nifty! At 1000 euro / m^2 a tad expensive though...

With the large amount of controllable channels, I wonder what they use. Constant current (switched) or PWM (linear)? At 1000 euro they do have the budget to do constant current, but still... not sure.

I looked into it a bit, and couldn't really find any ICs for multi-channel (as in 16 or so) constant current drivers.

The multi-channel PWM variety seems to be readily available enough from the likes of TI, and are used in led jumbotrons and such. Stuff like the TLC5943... Buuut, that means linear current source which generally is not as efficient as a switched solution. The main drawback of using switched is it's cost, which is considerably higher what with all the extra parts. And to keep dissipation for a TLC5943 to a minimum you could use something to provide headroom control, but that would add cost + complexity as well.

So all in all, I wonder what they use. Anyone got any ideas?

[pretmetled]

Well, a bit of reverse engineering later it seems plausible that they used constant current. Probably loads of 24 Volt capable dimmer bricks somewhere in the 8 - 10 Watt range.

[AnAppleSnail]

It looks like the video walls I used to set up for stage shows. LED panels with RGBW pixels 1-2cm apart. That spacing works from 50+ feet away to make seamless video. I think blue/white only with a diffuser would work at that spacing. I do not know the cost of these video walls, but I do know that they are re-used and often grabbed second-hand from high-dollar sales displays. One group had their players on a set of circular risers originally used in a BMW car show or something.

[pretmetled]

Your guess indeed isn't too far of. From what I was able to puzzle together they have RGB/W pixels spaced at a little under 2.5 cm. So an alternating grid of RGB leds and white leds. And as you point out with blue/white you can already do a lot of things in the "looks like a cloudy sky" department. For prototyping I'm looking to use R,G,B,W to see what is really needed and what can be done without. And green leds being pretty expensive are a good candidate to be removed.

Another variation on this theme that I just might end up trying is to have red, blue, cool white and warm white on the panel. Or 50% of the panels with R/B/warm white and 50% of the panels with R/B/cool white. The choice to reduce # of channels per panel also depends a bit on controller cost...

I do not know the cost of these video walls, but I do know that they are re-used and often grabbed second-hand from high-dollar sales displays.

Well, if you happen to know where such can be had for a nice reduced price that would certainly be interesting! I don't mind DIYing at all, but if the price is right I'm not above getting something ready to go and merely playing systems integrator.

[AnAppleSnail]

Well, if you happen to know where such can be had for a nice reduced price that would certainly be interesting! I don't mind DIYing at all, but if the price is right I'm not above getting something ready to go and merely playing systems integrator.

RGBW walls are made in relative bulk. Design for Manufacturing gut instinct tells me that setting up parallel production lines to produce stripped-down to Blue/White might not save money compared to buying bulk LED walls. Give these folks a call and see what you can arrange. The market isn't large enough to have the used ones on eBay very often.
Looks about right

Your best bet is to know someone in charge of a show or a group of these who is upgrading soon.

[pretmetled]

RGBW walls are made in relative bulk. Design for Manufacturing gut instinct tells me that setting up parallel production lines to produce stripped-down to Blue/White might not save money compared to buying bulk LED walls. Give these folks a call and see what you can arrange. The market isn't large enough to have the used ones on eBay very often.
Looks about right

Your best bet is to know someone in charge of a show or a group of these who is upgrading soon.

Looking for old RGBW walls I had not really considered. I'll keep an eye out on that from now for opportunities. That particular one you linked to looks to be a bit too high density for my needs, but the idea is a sound one!
So here's hoping someone needs to get rid of low-density high-efficiency RGBW walls anytime soon.

[AnAppleSnail]

So here's hoping someone needs to get rid of low-density high-efficiency RGBW walls anytime soon.

The stage walls are designed with a pixel pitch to produce HD or higher video quality from 30 meters and further. With diffusers you could get away with lower density as the lights shining on the diffuser would spread more - but you'd lose output and trap heat.

[pretmetled]

The stage walls are designed with a pixel pitch to produce HD or higher video quality from 30 meters and further. With diffusers you could get away with lower density as the lights shining on the diffuser would spread more - but you'd lose output and trap heat.

The trapped heat + light loss is indeed an unfortunate side effect of the diffuser. But a straight up HD display on the ceiling might not work so great as office lighting. XD I mean what with all the ceiling staring no work would ever get done!