If it was green it was probably VFD (Vacuum Fluorescent Display) tubes. Back in the early days when I rode my stegosaurus to school, manufacturers would make them into tubes with a single or a few digits inside. They're commonly used in a lot of things even today, except that they have a lot more characters and/or symbols inside. A microwave oven is a typical candidate, especially if you have a lot of little words like "cook time" or stuff that light up when you use it. Here's a bunch of examples: https://www.google.com/search?q=vfd+display+tubes&rlz=1C1ZCEB_enUS945US946&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi__IvhjcH3AhULZc0KHVgFCxUQ_AUoAnoECAEQBA&biw=1920&bih=969 (sorry, google)