if the convergence point would be 100000m behind the flashlight just the divergence would be really low about 0.000001mrad if the lens diameter is 10cm

lets say at 1m I got 100cd

now I got to to 100.000m then my spot is exactly 20cm

so at 100km of the flashlight I get 25cd

if I calculate that lux to 1m I get 25,000,000,000cd

if I measure at 300.000km or one light second

I get a spot of 600m

0,0000027cd

If I calculate that to 1m

I get 250,000,000,000cd

**so for this almost perfect thrower the distance to get an accurate reading would be a couple of light seconds away**

there will be a point where the cd doesnt raise anymore

how far that is away depends on the divergence and lens diameter

**as flashlights are really bad on divergence that point is really close to the light 5-10m should be fine**

just go further out and when the calculated CD value dont increese anymore the reading is accurate

you are just not understanding the difference between a flashlight and a laser

take a laser pointer with 3mm beam and 0.25mrad single Mode diode

I measure at 0m 10000cd

at 1m 3mm+(0,25mrad*1m)=3,25mm spot

measured 8521cd

at 2m 3mm+/0,25mradx2m)=3,50mm spot

measured 7346cd

if I calculate that to 1m I would get 29384cd

at 100m 3mm+(0,25mrad*100m)=28mm

measured 115cd

if I calculate that to 1m I would get 1,150,000cd

at 100km 3mm+(0,25mrad*100,000m)=25003mm

measured 0,00144cd

if I calculate that to 1m I would get 1,440,000cd

**for a Laser that will be in the range of a couple hundred meters to kilometers**

**it all depends on ratio for divergence and lens diameter**

I got 15 years experience with lasers also calculating things trust me