Does LED make for a good strobe?

"Jordan"

The phosphor has quite a long persistence.

... Phil

Jordan schrieb:

Hello,

I did that, if the flash is short enough you get a good image. If there is ambient light your strobe should be brighter.

Bye

Phil & Uwe,

Very good, thank you.

Jordan schrieb:

Hello again,

an example for the needed flash time. A wheel rotates with 3000 revolutions per minute and it should move not more than 1 degree during the strobe flash. There are 50 revolutions per second, one revolution is 20 ms long. 1 degree is 20/360 ms or 55 µs. Some 10 microseconds will do.

If the flash is 1/1000 second long, the wheel will rotate 360/20 degrees within that time, 18 degrees, this is not a sharp image.

Bye

Thanks Uwe,

Does your project use a triggered switch that is synchronised with each turn of the rotor? Is there available a circuit diagram?

Google works...

If you want to get a little fancy with the inductive pick-up (or you're too lazy or uninspired to make your own), you can get a professionally-made one through eBay;

Interesting, these have no positively timed pulse, very simple thanks.

They are excellent value for money.

Jordan schrieb:

Hello,

it was a complex project to measure sedimentation inside a rotating centrifuge using digital image processing. The strobe was only a subsystem for lighting the probe glases. I used about 20 RGB LEDs to select red, green, blue, yellow, magenta, cyan and white light. A IR reflective sensor was used for triggering. The duration of the LED pulse was selectable in steps of 10 µs up to 200 µs.

The circuit is not useful for an automotive strobe.

Bye

For an automotive IGN strobe, you could possibly use a UV security marking pen to highlight the timing marks and strobe it with a UV LED.

Might work better still with a background of white correction fluid applied first.

Thanks for the info. The strobe I want isn't for auto ignition timing, but to illuminate a "stopped" image of a spinning part, which does happen to be in an engine (with a glass window to see through). Colour isn't important as long as it's visible. It needs to be as compact as possible and heatsink type LEDs probably won't be easy for this, so I'll use the brightest probably 5mm diameter LED I can find. For the brief duty cycle, maybe I can get away with much higher current to get higher brightness.

Point taken about white LED persistence - good info. Does it happen in the LED, or the human eye? Those RGB LEDs are probably too big, but they look pretty nifty and I should buy one just to play with!

"Jordan"

Try reading mine again pal, its number 2 in the thread.

...... Phil

"Jordan"

Human eyes do NOT respond well to light pulses less than 1 millisecond long so the ambient must be near darkness to have any chance.

Really, a Zenon tube is a far better bet - they are very efficient and can produce huge amounts of light.

A compact, battery operated one is not hard to make - throw away cameras have the basis of what you need inside.

That is the way to go.

.... Phil

Why not a laser diode module with a diverging lens to give the size of spot needed.

Jordan schrieb:

Hello,

if you want to illuminate the spinning part with one 5 mm LED only, you need:

very low ambient light the LEDs should be close to the spinning part. only a small area should be illuminated a superbright LED should be used green light would be most efficient for human sight

Bye

The disposable camera option has one or two gotchas - the most common type is powered by a single AA cell and designed for single shot with a significant recharge time, it might be tricky getting enough power through the transformer for repetitive flash.

Winding your own bigger transformer on the basis of the original is complicated by an extra winding in series with the capacitor charging circuit that augments the base drive pulses - as the capacitor charges to maximum; the augment current tails off to conserve the battery. This feature offers no advantage in a repetitive flash application.

Some disposable cameras have a slide switch for the flash - but increasingly they have a push button and a few extra transistors for a latch controlling power to the flash circuit.

Its a matter of preference - but when I needed a 6V powered strobe for timing small motorcycles, I used a push-pull inverter.

You can also get green "dayglo" paint to highlight the target to make it even more conspicuous.