[time-nuts] White LED's

[Robert Atkinson]

Hi Dave,Yes I have. There was also a design in Nuts&Volts a while back. Generally if you keep the duty cycle low  (<1:20) and pulses short (<20ms) you can push most LED's to about ten times their maximum continuous rated current without ill effect. Looking at the continuous and pulse ratings of IR LED's can give an idea of the "abuse" LED's can handle. Some small white LEDs do have pulse specifications, they are used as the flash in cell phone cameras.  They make very good small strobes with much less "tail" than the $200 miniature Hamamatsu xenon tubes we were comparing them to. 
Robert.G8RPI.

--- On Sat, 30/1/10, Dave Martindale <dave.martindale at gmail.com> wrote:

From: Dave Martindale <dave.martindale at gmail.com>
Subject: Re: [time-nuts] White LED's
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Date: Saturday, 30 January, 2010, 19:12

Hmm.  Has anyone built a strobe light using LEDs instead of a xenon flash tube?  I can see the appeal of building something that doesn't need high voltage to fire or trigger the tube.  Yes, you probably couldn't get as much light as a big Xenon tube, but there are applications where you don't need to illuminate a large area.  (Recent example of where I wished I had a stroboscope: looking at the balance wheel of a pocket watch).

How high can you push the drive current of a LED if the pulse is short?  Of course you have to keep the average dissipation below what the device is rated for, but there must be a peak current limit too.

    Dave

On 30/01/2010 01:17, Robert Atkinson wrote:
> Hi,I'm late to the thread (as usual), but have looked at these LED's in the past. It was for a biotech imaging application. There are two types, a red/green/blue cluster or a blue / near UV LED with a white phosphor. These phosphors seem to have a fairly continuous spectrum, at least compared to fluorescent lamps and HID lamps. What surprised me was the speed. We had a strobe application for which a xenon strobe was proposed. I tried LED's (our optics "expert" said even normal LED's would not be fast enough). I knew normal LED's are fast enough but was unsure about the phosphor types. To my surprise they where faster than the xenon tube! They were faster than my detector. This has has an impact on the mill illumination in that you can get strobe effects that could cause you to think the spindle was stationary when it was not. This is more of a problem in a noisy environment than a home shop with only one machine running.  Robert G8RPI.
> 
>    



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