120V COB LED as strobe light - Page 1
Forum section: electronics / projects

author: dj_segfault
author_rank: Newbie
timestamp: May 30, 2019, 07:42:58 am
content: I DJ casually, and built my own Arduino-based lighting controller. I recently built a lighting fixture that uses 120V 50W COB LEDs driven by solid state relays. They work fantastic as long as they have a big heat sink.I got the idea from trying to make them flash quickly that maybe I could have the Arduino switch them on and off a few times a second to make a really bright strobe. Before I try it though, I'm wondering if that would create a lot of wear on the LEDs that will make them fail quickly. I assume the solid state relays would be fine. Am I right to be concerned, or will this be safe to do?Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: May 30, 2019, 11:54:59 am
content: I doubt it will work. The relay is unlikely to be able to switch them on and off fast enough.It could increase wear as every time they're turned on, the capacitor smoothing charges.To strobe an LED, you need a bare LED, with no driver circuit. A mains powered LED, with a built-in driver will not be designed for strobing.

author: dj_segfault
author_rank: Newbie
timestamp: May 30, 2019, 04:09:02 pm
content: I didn't think a solid state relay would have a smoothing capacitor, but you're probably right that the driver circuit on the COB LED would not do well. Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: May 30, 2019, 04:52:39 pm
content: Quote from: dj_segfault on May 30, 2019, 04:09:02 pmNo the relay won't have a smoothing capacitor, but the LED quite likely has one.A solid state relay will most likely be the zero crossing type, so the shortest possible on time will be half of the mains cycle.

author: DaJMasta
author_rank: Super Contributor
timestamp: May 30, 2019, 04:59:06 pm
content: That said, if your LED driver has a control input, you may be able to use that. The driver itself with input switching probably can't manage more than a few Hz, tops, for toggling, but likely manages less, but if it's PWM capable, it can definitely switch the LEDs fast enough, you've just gotta see if it will accept a very slow control input. There's a chance it could be moddable into the existing circuit as well, but it's probably more effort than its worth since they're likely pretty tightly integrated, undocumented, and involve mains voltages.

author: Zero999
author_rank: Super Contributor
timestamp: May 30, 2019, 09:40:13 pm
content: Quote from: DaJMasta on May 30, 2019, 04:59:06 pmDimmable LEDs, which accept a PWM input don't directly use the input signal to modulate the LED. It's normally low pass filtered first and the LED driver uses the resulting voltage to determine the brightness of the LED by adjusting the current or duty cycle.A simple on/off control input stands more chance of working.

author: Someone
author_rank: Super Contributor
timestamp: May 30, 2019, 11:27:08 pm
content: Quote from: dj_segfault on May 30, 2019, 07:42:58 amThere are several different lighting effects a strobe can be used for, but they all rely on very short duty cycles. A typical flash lamp has a duration of less than 1ms, stop motion effects are still usable with led lighting up to 20-40ms or so durations. The classic multiple images effect however needs 100-1000Hz repetition rate:https://en.wikipedia.org/wiki/Stroboscopic_effect_(lighting)LEDs can do this but they need very special drivers right in/at the fixture.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 31, 2019, 06:21:21 am
content: Even if everybody says "no" (they do for good reasons), you can still try just strobing it with your solid state relay, especially if you don't need long use cycles or long operating life. You won't lose much by trying.I was surprised how well such a product sustained on/off cycles. It was with DC input, sure, but in any case, with internal DC/DC converter and quite a lot of input capacitance. I strobed the light at around 15Hz for more than an hour with no ill effects, which would translate into over 50k on/off cycles. Would have been interesting to carry on until destruction.Adding a bit of series resistance (a heater element in series, for example) to take the edge off the inrush current could help.