Super lo-tech LED illumination for your microscope
by Martin Yarwood, Hampshire, UK
I recently got hold of an ex-educational microscope because it was surplus to requirement from my daughter's school. Because the bulbs were expensive and the transformer had finally broken, they decided to cut their losses and chuck it out. So first task was to find a way to replace the illumination so I found an incandescent bulb that did the job, but after a short while I realised it was insufficient for x800 magnification, there just wasn't enough light. I really had to work in the dark to be able to see. And an added downside was the housing got a little hot so I wasn't happy running it for more that 10 minutes. I read up a little on halogen and LED sources and while halogen sounded attractive because I would be able to easily source the bulbs I was concerned about too much light damaging my eyesight and It seems you need a IR filter to remove the damaging IR light.
So that would just beg the question where would I source a suitable IR filter. So turning to LEDs I realised I would have to do some research on what would be bright enough and how I would mount it accurately enough to ensure the narrow angle beam would enter the condenser correctly. So off to Maplin I went to find what LEDs were available. But while I was looking I found a torch that had an array of 9 ultra bright LEDs, see figure 1. There should be plenty of light there and they come in a housing that points them all in a plane with a suitable power source -no circuitry to design or construct. I just had to saw it up into suitable sized bits and reconstruct it to fit the housing under the condenser. I sawed the LED housing from the top of the torch barrel to make it shallow enough to fit in the base of my microscope under the condenser. I then reconnected the now three separate components with solder joints and bell wire, see figure 2.
I was amazed by the difference I could see immediately. I had enough light to need to use the diaphragm to limit it. The polariser worked over a greater range of angles before it became too dim. And the biggest thing seems to be that because of the quality of the light that was emitted of a diode, I could discern textures on the surface of cells, see cilia beating and see detail within cells that before I couldn't. The colour is a nice blue/white and being toward the blue will have a shorter wavelength that may help resolution. I don't have any UV details on the torch but being a consumer item I can't imagine it puts much out and unlike IR, UV is reflected by glass so I don't think I need to worry but I'm unsure about that as I have used it for a purpose it wasn't designed for*. So for £4.99 and a few hours work I seem to have upgraded my microscope very nicely. I'm even considering removing the mains cable and only using the battery/LED combination from now on.
Nine LED Rubber Torch only £4.99 Order Code: A78RN
from Uni-com global ltd 1&2
Enterprise way Edenbridge Kent TN8 6EW
All comments to the author Martin Yarwood are welcomed.
*Editor's note: A white LED is unlikely to have any UV emission judging from the spectra published of other much higher power white LEDs.
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