ran my deauville bike so the needle was in the red just touching the bottom of rhe longer red marker. 19 litre tank took only 16 litres meaning even then I had 3 litres left. Shame there isn't a reserve option when you have a gauge....
Don't bet a long walk on having those 3 litres. At least here in the USA, the listed tank capacity is for a full tank. But about 10% or so is above the filler neck so as to give room for fuel expansion, so the fuel won't dribble out past the fuel cap when the fuel warms up on a hot day.
I always run the tank low into the red. I ran the wifes Dodge Cailber out on purpose (had a fuel can in the back) so I could see how much it took before the low light went out. Turns out there is 3 gallons when the light comes on. And I topped it off with a total or 20 gallons! The manual says its only 13.5 gallons.
My Jetta says it's 14.5 gallons and it always takes 14.7 when the light comes on. I know of a guy running his TDI out of fuel and it took 17.6 gallons to completely fill. The point is, there is usually more in there than you think.
I usually run my tank far beyond the low fuel light dash indicator. My Subaru is spec'd with a 16.9 gallon tank capacity and this morning I filled it to the first 'click', it took 15.2 gallons. If I can believe Subaru, I still had another 1.7 gallons left (and ~50 miles). The 'low fuel' dash light came on about 75 miles earlier.
Basically there's always loads left, the main reason is car manufactures always cover thier own butts. Lets say someone ran out and broke down in the middle of the highway, which caused a fatal accident, well I need not explain who would be liable for saying "there's plenty left" and in America, people sew anyone for anything so it could cost millions!
In my opinion it's never a good idea to regularly run the fuel tank down to the bottom as any particulates that have settled there will get picked up and fed into the system causing fuel filters to clog up much more quickly. Running it down once to see how close you can get it is fine, but then give yourself a margin for error thereafter. And who needs a light to tell you when to fill up? What's wrong with using the gauge and a bit of common sense ;-)