A Welch Allyn
A long while back, while in a doctoral program, I landed a job in an Ophthalmology department.  It was fun and I learned a lot; enough to start a small company that made the first diamond surgical scalpel.

While we were doing that, the company needed to have some "cash incoming".

During my department days, every office had a projector that, well, projected the letters you read for an eye know...the big "E" chart, 20/20 all that? In those projectors rested a special bulb that was very bright and got really hot. Mostly it had a "secret" set of socket hookups so the only use was for that projector.

These bulbs blew out all the time. The doctors left the projects on all the time; mainly because the project got so hot it would burn you.  Hence they blew out all the time.  The cost the medical center about $6.00 a bulb 40 years ago.  We spent a fortune.
Welch Allyn Bulb
$34.95 on e-Bay

Our little diamond knife company was pretty close to a GE wholesale distributor - a small company that supplied light bulbs to grocery stores on routes.  I used to play tennis at a club and at one point was, one day, paired with the owner. We talked about light bulbs.  He was the Forrest Gump of light bulbs (rather than shrimp).

Appliance light bulbs
$7.99 EACH
I mentioned the light bulb in the ophthalmology projectors and he said, "Hey come on over. We might have something you can use". Indeed he did. Cases and cases of them. Big BIG cases - 5,000 bulb cases. "Gosh, no one every uses these..they just sit around". How about $1.00 a bulb and I'll pay you in 30 days. "If you pick them up - ALL OF THEM - you got a deal".  I now owned 40,000 bulbs.  I also owed $40 grand.

We sold them to suppliers as fast as we could ship them. They were used to buying them from GE at $4.00 each so we offered ours for $3.00 plus S&H. It took two hours on the phone to sell 40,000 bulbs. Cash. We bought 40,000 more the next month - special order. The diamond knife was created, funded, and brought to market on the back of light bulb sales.

I was in the local King Kullen supermarket yesterday and went by the light bulb stand. One of the lights over our stove blew out and so I was a "buyer".  The price was $7.99 for a "SPECIAL BULB".  The nerve.

I don't need to fund the development of the diamond knife but I see an opportunity.