Here's my version, using stuff I had on hand.
Unfortunately, we didn't have a suitable solar panel and my husband wasn't up for running to the local supplier for one, so I have to wait a bit before it's completely finished to my liking. I designed the shape so the small solar panel can rest on the back at an angle and charge during the day if one leaves it in a sunny windowsill.
I wanted the mushrooms to resemble the real luminous mushrooms and glow for awhile after it was turned off.
Step 1: Prepare the log
A smooth, decaying stick I found in the strawberry bed seemed aesthetically pleasing... but all the cracks almost guaranteed lots of bugs.
The maple branch I'd removed from our tree a few weeks ago was almost certain to have very few things that might crawl out and bite me, but it just wasn't very interesting to look at.
Finally, I decided on the root end of some evergreen bushes I recently ripped up. I didn't see any holes where bugs might be hiding, and it was definitely interesting to look at. I washed it with the hose, broke off the extra branches, and dried it in the oven at 200 degrees for a couple hours. That way, any bugs would hopefully die.
I then drilled holes where I thought mushrooms should go.
I decided to put the wiring etc in the back, rather than hollowing out part of the log. The solar panel would have to be visible, anyway.