The idea of lighting from below is one I had not thought about. Just did not enter my mind but there would have been problems in this case anyway.
This is the bottom section of the orb I had and it is an opaque plastic as well as being the base for the orb to rest on when in place.
The bottom had a setup for adding air to be used with an airstone or filter but I didn't want that so took it apart to see how it might work for other things.
Once removed, I saw a handy use for the airline hole.
Cutting the plastic center "cup" off gave me access to run the probe for the temperature controller into the tank without it showing.
I've found these little cheap probes to be "water resistant" but fail after being in the water for a few months. That leads me to always seal them so that they can read the temperature but stay dry.
In this case I pushed the probe up into the existing airline fitting, inside a small section of airline tubing and sealed it. This lets me extend the probe up near the center of the water column rather than down near the heat source, hoping to get a more accurate reading.
For the filter in/out I just used a couple simple fittings that I could find easily. Outside is a brass NPT to barb fitting, screwed to a small nipple and then inside is the same. For sealing I used a rubber type washer backed with a metal washer both inside the tank and on the outside. Leaks are not something I want to find some day. The threaded adapters are screwed tight enough to compress the rubber and make the seal.
I have never kept any fish who had a problem with metal in the water.
The tubing inside was left long at this point as I had not worked out how much was needed and it was easier to cut off later than add later.
Sealing the airline tubing is a pretty simple thing since it is plastic. I set the end on fire and clamped it with pliers. When it cooled the end was sealed!
Meanwhile I set it up in the garage, filled it and let it set for a few days while I worked out the wood to cover the outside and built the light. The original light was pretty lame when new and a part seemed missing so after looking it over, I decided I would go for a DIY LED rather than spend time on the old.