http://confocal-microscopy-list.275.s1.nabble.com/Guidance-wanted-on-illumination-stability-tp5784748p5788687.html
It is not only possible, but Thorlabs sells an LED controller that modulates LED intensity in this way up to 10kHz which I think should be adequate for the effect discussed in the Hell paper. I have not had a chance to try it yet and see if it works to reduce bleaching. Dave
> *****
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>
> It might also be useful to have pulsatile LEDs operating in the
> nanosecond range - there was a Stefan Hell paper that showed very
> significant reductions in photobleaching when the gap between pulses
> was longer than the fluorescent lifetime. Is this possible with LEDs ?
>
>
> Quoting Gordon Scott <
[hidden email]>:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
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>>
>> Hi Guy,
>>
>> No the copy strategy didn't work. Of course one only finds that out
>> after the event. Ho Hum. :-(
>>
>> My original thoughts on video were as yours, however I _think_ most
>> cameras take a full image and then the lines are downloaded
>> sequentially, but I'm also very aware that that may not be the whole, or
>> even the correct story. If the line rate _is_ important, and I guess if
>> the data is downloaded from the camera `live' line-by-line, rather than
>> as a complete image, then 100kHz will definitely show artefacts and the
>> case is closed .. I need to keep the linear control.
>>
>> The main aim is actually to avoid unnecessary waste heat, though saving
>> money is always nice. I'm not sure it would make a particularly
>> significant effect on price, but it may. Any waste heat I have I then
>> have to get rid of. LEDs must not get as hot as bulbs and indeed we
>> actively cool them to get the best out of them, so getting the excess
>> heat out of the boxes needs heat sinks and fans or similar. At present
>> that waste heat puts a frustrating limit on what's feasible with the
>> units, and I'd like to remove that frustration.
>>
>> Thanks for your 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: Guy Cox [mailto:
[hidden email]]
>>> Sent: 29 November 2010 23:15
>>> To: Confocal Microscopy List
>>> Cc: Gordon Scott
>>> Subject: RE: Guidance wanted on illumination stability
>>>
>>> Gordon,
>>>
>>> Your strategy of copying to the list didn't seem to work.
>>> Anyway, I think that lots of list members, having seen the
>>> question, like to see the answers.
>>>
>>> If someone is taking conventional images with a 1
>>> second exposure 100kHz ripple will not be noticeable. But if
>>> you are taking video at 25 fps 525 line (international video)
>>> your line rate is about
>>> 13 kHz (US video about 14kHz) so I'd imagine there would be
>>> rather unwelcome diagonal stripes on the image and you'd be
>>> getting angry phone calls from your customers.
>>>
>>> You haven't told us the other side of the
>>> trade-off. Do you want to eliminate the linear stage to save
>>> money - if so, how much cheaper would it make a CooLED
>>> illuminator? Or is it to save power?
>>> How much would that save? Given that an LED source already
>>> uses hugely less power that an HBO 100 mercury lamp, would
>>> anyone care?
>>>
>>> Guy
>>>
>>> Optical Imaging Techniques in Cell Biology
>>> by Guy Cox CRC Press / Taylor & Francis
>>>
http://www.guycox.com/optical.htm>>> ______________________________________________
>>> Associate Professor Guy Cox, MA, DPhil(Oxon) Australian
>>> Centre for Microscopy & Microanalysis, Madsen Building F09,
>>> University of Sydney, NSW 2006
>>>
>>> Phone +61 2 9351 3176 Fax +61 2 9351 7682
>>> Mobile 0413 281 861
>>> ______________________________________________
>>>
http://www.guycox.net>>>
>>>
>>> -----Original Message-----
>>> From: Confocal Microscopy List
>>> [mailto:
[hidden email]]
>>> On Behalf Of Gordon Scott
>>> Sent: Tuesday, 30 November 2010 2:34 AM
>>> To:
[hidden email]
>>> Subject: 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>>> *****
>>>
>>> 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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>>
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