Searching the forum, it appears that this hasn't been discussed here before, so here are the details:
Firstly, this is NOT my idea: full credit must go to the creator on this page https://www.gemologyonline.com/Forum/ph ... 21&t=18097
Here are a few images and instructions to help those who wish to perform the mod.
In addition to the Jansjo light you'll need a wine bottle cork (the happy by-product of wine drinking) and a "Universal Tip Guide Optic Fiber Rod for Dental Curing" - i found mine here on Aliexpress
https://www.aliexpress.com/item/1-PCS-8 ... 90351.html
The cork needs to be cut to about 1cm long, and then a hole bored into the centre of the flat side of the cork. Examine the cork before cutting - they are usually thinner at the top end of the cork (i.e. not the end that is in contact with the wine when the cork is in the bottle), and the top end fits more easily into the Jansjo lens holder. I used the blade of a small penknife to bore the hole, but you have to be slow and methodical to avoid the cork splitting or cutting yourself - it just so happened that the width of the blade i used was almost the same as the width of the end of the optic, but you want the fit to be quite snug.
Next fitting to the Jansjo. Using a thin blade, gently prize out the lens and lens holder from the Jansjo light by sliding the blade in at the top or bottom (where the screws are visible) between the black lamp housing and the clear lens holder.
Once you have freed the clear plastic lens holder, slide it over the end of the cork. There are two holes in the sides of the lens holder that clip into place when inserted into the light housing - the cork should not cover these holes.
It easier to get the cork inserted into the lens holder, then inserting the fibre optic rod into the hole in the cork, which, if you made the hole sufficiently snug fitting, should push the cork out slightly and create a secure fit with the lens holder.
Comparing the output (the head of each Jansjo is at the same distance from the paper), the removal of the original Jansjo lens makes a noticeable reduction in the yellow fringing around the edge. Left the Jansjo LED fiber optic light guide, middle shows a 10x loop attached, and right the unmodified Jansjo. Perhaps the biggest benefit is the ability to more precisely position the focused light from the optic rod. I cut a small disk from a ping pong ball just slightly larger that the tip of the optic rod, and attached it with tape to produce a more diffuse light.
In place on my rig.
jon
edit - moved this to this forum after accidentally posting to the "Macro and Micro Technique and Technical Discussions"
This approach could be implemented on the popular Convoy S2 Nichia UV flashlight* for fluorescence as the fiber optic tip seems designed for UV cure and would allow to put the light source much closer to the specimen with microscope objectives.
This is a nice and useful addition to our pages.