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Hi Craig,
Oh, my apologies, I'm inadvertently misleading the list here, sorry.
I'm part of CoolLED and I'm looking at how we improve and move forward
our illumination products.
My concern is that what we think might be acceptable in a new product
may not be acceptable to end users. My suspicion and also your 120Hz
sampling comment suggests that it quite possibly isn't and that I need
to keep the linear control. 100kHz/25% ripple at 120fps would appear to
be a brightness range around 0.025%, which should be invisible, I think.
On the other hand if the camera scans lines for whole frames, that jumps
to, say, 16% (640 lines), which is very likely intolerable. I'm also
concerned about it in techniques like FLIM where time performance is
significant.
Thanks fro you comments.
Kind regards,
Gordon.
--
Gordon Scott Design Engineering
Custom Interconnect Ltd. http://www.cil-uk.co.uk
CoolLED http://www.coolled.com
CoolLED is a division of Custom Interconnect Ltd.
Phone +44-1264-321321
CIL House, Charlton Road, Andover SP10 3JL, UK
> -----Original Message-----
> From: Confocal Microscopy List
> [mailto:[log in to unmask]] On Behalf Of Craig Brideau
> Sent: 29 November 2010 17:56
> To: [log in to unmask]
> Subject: Re: Guidance wanted on illumination stability
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> It really depends on your acquisition and what you are trying
> to see. For instance if you are using a camera with long
> exposure time then the ripples will average out in the image
> and you won't have a problem. On the other hand if you are
> sampling at say ~120 Hz you will have alternating dim and
> slightly brighter images. This may be a problem your users
> can live with, depending on what they are looking for.
> Finally, if you are aware of the noise and its frequency AND
> it is consistent then you can probably subtract it out
> post-processing.
>
> Craig
>
>
> On Mon, Nov 29, 2010 at 8:33 AM, Gordon Scott
> <[log in to unmask]>wrote:
>
> > *****
> > To join, leave or search the confocal microscopy listserv, go to:
> > http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> > *****
> >
> > Hi Guys,
> >
> > I'm looking at ways to further improve the performance and
> efficiency
> > of our light sources.
> >
> > There are always tradeoffs when doing this and I'd like to better
> > understand what tradeoffs are acceptable for real microscopy users.
> >
> > Our present illumination sources all use a switched-mode
> > pre-regulation and a linear final regulation for the LED power, so
> > ripple is very low, but at a cost for us of some power
> wasted in the linear stages.
> >
> > I can improve that efficiency and reduce the waste by foregoing the
> > linear stage and regulating directly with the switching
> mode, but the
> > tradeoffs are a longer On/Off switching time than is feasible with
> > linear, and a high-frequency ripple.
> >
> > My simulations suggest switch-on and switch-off times of
> around 50us
> > and a ripple of around 25% at 100kHz, which would be
> reasonable from
> > an electrical/energy point of view.
> >
> >
> >
> > The question is, of course, would any of the people likely
> to use it
> > find that performance difficult or unacceptable?
> >
> >
> >
> > I've copied to the list rather than posting direct, so
> hopefully the
> > replies will come to me rather than cluttering the list.
> >
> > Thanks for considering the question, even if you need not,
> or choose
> > not, to answer.
> >
> > Kind regards,
> > Gordon.
> > --
> > Gordon Scott Design Engineering
> > Custom Interconnect Ltd. http://www.cil-uk.co.uk
> > CoolLED http://www.coolled.com
> > CoolLED is a division of Custom Interconnect Ltd.
> > Phone +44-1264-321321
> > CIL House, Charlton Road, Andover SP10 3JL, UK
> >
> >
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