Soap film wind tunnel

Reservoir of soapy water at the top, needle valve to control flow, monofilament line forms the rails. Solution is collected at the bottom and pumped back to the top.

I first tried single color power LEDs to see interference fringes. I didn't observe very clear fringes. Then I switched to a low-pressure sodium lamp. I saw very clear fringes.

First videos

line

finger

I need to fix the flicker from the ballast for my low pressure sodium lamp.