advice needed on making meter measurements with a fiber optic probe

I was recently given a Gossen fiber optic probe that fits the LunaPro and similar style Gossen meters. I'm trying to use it to measure the absolute light output of various flat panel displays and am a bit confused on where I set meter sensitivity to arrive a meaningful readings. Has anyone done this using this probe? Does anyone know of a standard I could use to make a reference measurement? My goal is to be able to walk up to a flat panel display, make a measurement of the lightest and darkest areas of an image and document what the screen output is in foot candles or lux (which the Gossen meters will allow me to convert to using the chart on the back of th meter). Any help would be appreciated.

Not sure about the Luna Pro, but when the fiber probe is fitted to the Lunasix 3 the table in the manual states that when the needle points to the "1" it is reading 0.045 lux, etc.

Free program. LL-Pro. Measures lux, Kelvin, EV, shutter speed, aperture, etc after you input ISO on your iPhone. Lot faster and easier then using a probe on a CDS meter.

https://www.bhphotovideo.com/c/produ...pro_meter.html