Does LED make for a good strobe?

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Strobe lights are being made using LEDs.
But are they comparable to say Xenon lamps, as used for car ignition  
timing lamps. These are very effective at "stopping dead" the perceived  
image of a spinning part.
I'd like to make a compact, low power strobe, that won't give a blurred  
image. Any chance with LEDs?

Re: Does LED make for a good strobe?

"Jordan"
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**  Mostly only "party strobes" .


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** Not if using white LEDs.

   The phosphor has quite a long persistence.


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** Sure, use any colour or combination of "super bright" LEDs you like.



...  Phil



Re: Does LED make for a good strobe?

"Phil Allison"

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** Seems this info is wrong  -  like many others I had read comments about  
white LED persistence in more than one place.

In fact, the very lack of persistane is an issue with LED lighting that  
operates from 50/60 Hz sources - either rectified or not -  because it can  
produce annoying strobing effects.

BTW:

On a few occasions I have replaced the 6.3 volt bezel lamp on the front of a  
valve amplifier with a red LED and resistor.

Worked fine and no obvious flicker.


...  Phil



Re: Does LED make for a good strobe?


Jordan schrieb:

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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


Re: Does LED make for a good strobe?
On 14/06/13 19:17, Uwe Hercksen wrote:
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Phil & Uwe,

Very good, thank you.

Re: Does LED make for a good strobe?


Jordan schrieb:


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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


Re: Does LED make for a good strobe?
On 14/06/13 23:57, Uwe Hercksen wrote:
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Thanks Uwe,

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

Re: Does LED make for a good strobe?
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Google works...

http://www.eeweb.com/blog/extreme_circuits/automotive-led-timing-light

http://tehnikservice.net/2011/12/10/automotive-led-timing-strobe/

http://www.howtoalmanac.com/kevin/projects/automotive/timinglight.htm

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; http://www.ebay.com.au/itm/151048454876

--  
Bob Milutinovic
Cognicom


Re: Does LED make for a good strobe?
On 15/06/13 13:38, Bob Milutinovic wrote:

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

Re: Does LED make for a good strobe?


Jordan schrieb:


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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


Re: Does LED make for a good strobe?
On 14/06/2013 10:11 AM, Jordan wrote:
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**As PA has suggested, white LEDs possess too long a a persistence to be  
effective as a serious strobe light, but you can use RGB LEDs to provide  
a close approximation to white light. Speed is not a problem for RGB  
LEDs. I've used these in a recent project:

http://www.ledsales.com.au/catalog/index.php?main_page=product_info&cPath14%8_188_221&products_id77%7

They are excellent value for money.



--  
Trevor Wilson www.rageaudio.com.au

Re: Does LED make for a good strobe?


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http://www.ledsales.com.au/catalog/index.php?main_page=product_info&cPath14%8_188_221&products_id77%7

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.  


Re: Does LED make for a good strobe?
On 18/06/13 07:08, Ian Field wrote:
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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.

Re: Does LED make for a good strobe?

"Jordan"
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** You are dreaming if you think ONE ordinary LED will do it.

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




Re: Does LED make for a good strobe?


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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.  


Re: Does LED make for a good strobe?

"Ian Field"
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** Huh ?

Start by making the discharge cap about 100 times smaller -  ie about  1uF.



...  Phil





Re: Does LED make for a good strobe?
On 19/06/2013 9:03 AM, Phil Allison wrote:
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**Indeed. Flash tubes in typical cameras are rated for around 1 ~ 2  
Watts of average power. This assumes a cycle time in the order of  
several seconds. Discharging (say) 100uF or more @ 300 Volts at a rate  
of (say) 50 ~ 100 times per second will destroy almost any flash tube  
rapidly.

Funny this thread appeared this week. A couple of weeks back an old  
girlfriend asked me about the strobe light I built when I was in school.  
She wanted it for her daughter's art display. I dug it out and gingerly  
switched it on. The damned thing actually still worked! The tube flashed  
erratically, as it certaintly showed significant signs of many hours of  
use (at parties and nightclubs). It is a 5 Watt tube, which I managed to  
overdrive (at times) to around 10 Watts. Very forgiving things. Still,  
they do have limits and it is wise to remain within those limits for  
reliable operation. We decided to use an LED.

A high power RGB LED makes a lot more sense. Cheap and dead easy to use.


--  
Trevor Wilson www.rageaudio.com.au

Re: Does LED make for a good strobe?
On 19/06/2013 9:29 AM, Trevor Wilson wrote:
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Fujitsu used to use a bank of flash tubes as the fuser for their  
mainframe laser printers. Powering the tubes was a ferking big bank of  
capacitors. Lovely things to work on you grounded them with a foot long  
grounding stick, left them like that for 15 minutes, took it off for  
another 10 then waited another 10 minutes with the ground on again and  
left it on while you worked on the system.

Re: Does LED make for a good strobe?


Jordan schrieb:

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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


Re: Does LED make for a good strobe?


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


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