LED bulb/flood as strobe lamp

Does anyone have any data on how fast an LED bulb or flood lamp could be driven with a triac or something, at x number of Hertz slower than the "flicker fusion threshold", and have the results still be interpreted as discrete flashes? I'm assuming LED bulbs/flood lamps run off 120 VAC still do not have anywhere near the same thermal inertia that incandescents do.

Would driving them at a rate slow enough that they're not responding to the RMS value of the waveform cause any damage to the lamps?

Reply to
bitrex
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The commercial lamps probably all have power factor correction, and thus may not be able to flash much at all. You might only get 2 -5 flashes a second from them, and it might quickly burn up part of the power factor correction or inrush surge limiting circuit.

The bare LED section can be flashed several thousand times a second easily, but that requires internal modifications.

Jon

Reply to
Jon Elson

16Hz is certainly flicker, 100Hz certainly isn't. Between those it's a gradual change, there's no sudden threshold.

it's routine

NT

Reply to
tabbypurr

They have a crude constant current drive. Not sure how they do the dimmable ones but I doubt if any will react well to a strobe drive.

You would have to drive a bare batwing LED directly and stay inside its absolute maximum ratings for power dissipation and maximum current.

You can probably push the envelope a fair bit if you don't mind failures

- especially for short duration flashes widely spaced.

Smartcam flashes give an idea of what is possible.

I suspect pure RGB LEDs are quite a bit faster than the nominally white ones which are blue plus a relatively slow yellow phosphor.

--
Regards, 
Martin Brown
Reply to
Martin Brown

At least many 230 V LED bulbs remain lit for nearly a second after switch off, so they are not suitable for any fast blinking application.

Reply to
upsidedown

Where is the energy coming from to keep them lit? Our kitchen cans take a half-second to a second to come on but there is no delay on turn-off.

Reply to
krw

Phosphorescence.

Reply to
Tom Miller

Then how do you explain the sharp light cut-off after that delay ?

If phosphoresce, the light output would drop out exponentially as in fluorescent tubes.

Reply to
upsidedown

Not buying. That's a lot of energy.

Reply to
krw

The cheap LED bulbs I've taken apart seem to be nothing more than a nonpolarized voltage dropping cap, a bridge rectifier, and a couple current limiting resistors along with the LEDs inside an ordinary frosted plastic enclosure. They turn on and off instantly.

Reply to
bitrex

** The yellow light emitting coating used with white LEDs does not use "phosphorescence" and has no persistence.

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Lack of persistence commonly results in significant flicker in the light output at twice the supply frequency - made worse if used with a dimmer.

... Phil

... Phil

Reply to
Phil Allison

Capacitance in the LED PSU and some delayed phosphorescence in the yellow phosphor. Most of mine switch on and off more or less instantly so probably within a couple of mains cycles at most.

Cans?

I have never known any LED bulb to be other than instantaneous switch on and at full brightness too. CFLs used to take an age to get going.

Some LED bulbs will remain very faintly lit even when "off" to the properly dark adapted eye from leakage current in the circuit.

--
Regards, 
Martin Brown
Reply to
Martin Brown

Come on! A second? That's a *LOT* of capacitance. Why? Even one cycle is a lot for an illumination LED. Pick your numbers.

Recessed can lights?

Surprised the hell out of me. Quite upsetting not to have light instantaneously. There's enough delay that one may think they didn't flip the switch and do it again.

yeah, I don't like CFLs because of the long warm up time. The only place I have them is in the basement and I'll get around to replacing them with T15s soon enough.

Haven't noticed that but it wouldn't be bothersome. Feechur it as a nightlight. ;-)

Reply to
krw

I have observed this with several E14 base LED bulbs, possibly North Light or Osram brands..

It is in fact quite annoying, turning the light switch OFF and nothing happens for a while. My first thought was that the light switch was broken or arcing over, but this has happened with several switches and even with a mechanical timer in which you can hear the switch-off click but nothing happens for a while.

Reply to
upsidedown

Power from the ether! :)

Jamie

Reply to
M Philbrook

Well if the cap is on the 100V side of things then 10's of micro Farads might be enough.

George H.

Reply to
George Herold

Ether only gives the illusion of power.

NT

Reply to
tabbypurr

** A 100uF electro stores less than 1.5joules at 170V.

... Phil

Reply to
Phil Allison

I think we may be at cross purposes here. I didn't mean that the lamp maintains full brightness for nearly a second but that the last traces of illumination take about 1s to decay to total blackness. Much easier to see on a clear one where the dies are directly visible.

I think it mainly afflicts the crudest ones which seem to be more or less rectify the mains and power a long series chain of basic surface mount LEDs in a spiral. First one to fail wipes it out completely :(

Many of the latest generation come on and switch off just like a normal bulb - but some of the previous generation were slow to go off.

--
Regards, 
Martin Brown
Reply to
Martin Brown

** If you do not look directly at the lamp itself but the wall or floor in an otherwise dimly lit room - you will find the light goes out much faster.

FYI:

Eyes have persistence, but the yellow phosphor used in LED lamps does not.

... Phil

Reply to
Phil Allison

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