Build my own light bulb
If you only want 800degC then maybe you should try coiled nichrome wire. Cheaper, and you can use enough to measure the resistance accurately - it's used in electric fires. You can then work out the current needed to make it glow red hot because you know the mains voltage and (after you unwind it) the length coiled on the heater element. Then it's simply Ohms law or a lab PSU measurement.

Or you can assume it takes approximately mains voltage to drive enough current to make it glow red. So the same current will make any given length glow red.

Typically these are 1kW elements, so if you are in Europe the current is about 4 amps for a 230VAC mains.