[personal profile] eub
They're solar-powered, and they turn on as you get near them by Bluetooth. Waterproof of course. If they're pulsed LEDs to save power, that's great, just so as the frequency is high enough that I can't see the flicker.

(I will be very sad when they stop manufacturing incandescent Christmas tree lights and all the LED ones have that horrid nails-on-chalkboard flicker.)

If they have microphones and transmit the outdoor soundfield indoors for my listening pleasure, that would be a bonus. If they do it by micropower peer-to-peer meteor-bounce radio so I can scatter them on public lands, so much the better. They can even drop the whole lighting feature from those models if it helps meet specs.

Date: 2011-07-18 02:24 pm (UTC)
From: [identity profile] via-lens.livejournal.com
Sounds like you've got work to do there, Eli. These things aren't gonna invent themselves. ;)

Date: 2011-07-18 02:39 pm (UTC)
From: [identity profile] xuth.livejournal.com
all the LED ones have that horrid nails-on-chalkboard flicker
If you use a different power supply than just plugging them into a wall outlet you could change the frequency of the flicker. I presume they're just in several passive circuits with a bunch of LEDs in series with a resistor (as that's the cheapest way of doing this) but I've not carefully looked at any of them. Assuming this is true you could just use a 600 hz 120v power supply and you'd lose the obvious flicker (It would still be detectable with movement). If all of the LEDs were in the circuit in one direction (which I would hope they're not since failing to do so doubles the AC power requirements, but you could always rewire the strands) then you could just use a good DC power supply and have no flicker. Some ropelights are powered from DC so that they can be cut to length and (assuming a good power supply) should have no flicker.

Date: 2011-07-19 12:58 am (UTC)
From: [identity profile] randomdreams.livejournal.com
If there's any discernable flicker at all in a non-moving string, it's being run off 60Hz, probably with 120V dropped across the whole string, because it's cheap. As you say, any DC driver whatsoever will fix the problem. (We do flicker some of our LED drivers but in the megahertz range.)
However, an interesting proviso there is the non-moving part. If either the LED's or the person viewing them are in motion, *particularly* if the person is reading or rapidly looking from one side to the other (as you do when you drive) the safe frequency rises dramatically. There's research out there that indicates people exhibit signs consistent with eyestrain from flickering lights at strobe rates of over 10kHz in circumstances like car traffic where both eyes and light sources are moving fast.

Date: 2011-07-19 07:48 am (UTC)
From: [identity profile] eub.livejournal.com
Bless you for using MHz range.

I do see a lot of 60 Hz Christmas lights, as best I can estimate the frequency, by its streak pattern in a saccade as compared with a known AC-synchronous light. (It would be an interesting party game to see who can guess closest to the correct flicker frequency of an LED.)

I'm curious, if I see an LED duty cycle well under 50%, does that suggest an active driver generating its own frequency (that I can rightly berate for not making it higher), or is that a likely signature of a passive rectification setup too?

Date: 2011-07-19 05:06 pm (UTC)
From: [identity profile] xuth.livejournal.com
it's being run off 60Hz, probably with 120V dropped across the whole string
I should apologize. When I said I hadn't carefully looked at them it meant that I hadn't taken one apart, attached a meter to it, etc. Admittedly my sample size is very small but the LED xmas lights I have have a bunch of short (15 lights?) strands (each with a small box on one end or the other) in parallel with each other. Thus I made the assumption that the small box housed a small resistor and that the strands were set in alternate polarities to balance the load. The box advertises that you can string some ungodly number of strands together but I think the voltage drop due to the length of wire will be more of an issue than overloading the 18 or 20 gauge wires in use.



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