# help building an led light source for microscope with a dimmer control



## jx3 (Dec 7, 2008)

Hi I have been searching around on the forum and trying to learn enough about leds to build an led light source for an older microscope. Having the ability to adjust the light intensity is an important feature. I was thinking around 300 lumens, I have seen lots of led assemblies on ebay stating that they are compatible with lights such as surefire 6p, 9p etc. This looks about the size assembly that would fit in my scope where the original incandescent bulb went. I am limited to a maximum diameter of 26mm. Less than this would be fine as I could machine a sleeve for it. Or any other led assembly that someone thinks would work well, I would be running it off an external battery pack so voltage could be anything. I was thinking of using the buckpuck with external dimming to drive it. Am I correct in thinking that the buckpuck controls current to change the lamp output and does not use PWM ? I have read that PWM can cause problems when using digital cameras with a microscope as the camera picks up the led's flicker. Do these led assemblies already have a driver board built in ? if so would I be able to just connect the buckpuck driver or would I have to disable the existing driver ? Any suggestions and advice would be appreciated . Thanks John


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## LukeA (Dec 7, 2008)

If you use a buckpuck you will have to remove the existing driver. (not that difficult)


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## StarHalo (Dec 7, 2008)

Well this is interesting - the Philips 5761 bulb that we're so fond of using in hotwires is actually a microscope bulb. So now we're putting the microscope bulbs in the flashlights and putting the flashlight bulbs in the microscopes..

The big issue you'll have is heatsinking and output. The aforementioned incandescent microscope bulb (when driven at its correct voltage, not how we use it) puts out 600 lumens, so you're going to need a P7 or an M-CE, both of which require some very serious heatsinking.


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## romulus (Dec 7, 2008)

PWM is ok even for digital image capture, the key is to know your framegrabber rate, and setup your PWM frequency about five times higher.

I have played with buck-type ckts. they're great with discrete LED's, but if you're driving several lumens (>50), use a PWM ckt. that sinks current to ground - no messin around.

These folks do alot of custom work cheap, Check out: 
http://www.ledhot.com/smartleddivelight.html


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## LukeA (Dec 7, 2008)

StarHalo said:


> Well this is interesting - the Philips 5761 bulb that we're so fond of using in hotwires is actually a microscope bulb. So now we're putting the microscope bulbs in the flashlights and putting the flashlight bulbs in the microscopes..
> 
> The big issue you'll have is heatsinking and output. The aforementioned incandescent microscope bulb (when driven at its correct voltage, not how we use it) puts out 600 lumens, so you're going to need a P7 or an MC-E, both of which require some very serious heatsinking.



Provided, of course, that the microscope in question uses that particular bulb. Also, keep in mind the difference in emission pattern. A 5761 putting out 600 lumens will only get as much light on target as an XR-E at high current.


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## 2xTrinity (Dec 7, 2008)

LukeA said:


> Provided, of course, that the microscope in question uses that particular bulb. Also, keep in mind the difference in emission pattern. A 5761 putting out 600 lumens will only get as much light on target as an XR-E at high current.


You can't generalize that, it will depend on the optics used to collimate the light from the incan, and the LED respectively.

Granted, a forward emitting device like the XR-E can be potentially easier to collimate. Instead of an elliptical reflector + lenses to form a projector assembly, the right TIR optci shoudl be able to do the trick with fewer losses. But using the best availalbe optics for the incan, and LED respectively, there won't be a 3:1 improvement.

There may be a 3:1 difference between a DIY incan, and DIY LED design hwoever, as designing projector assemblies to work with omnidrectional light sources is not trivial.


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