Hello Overload,
Crag has it right. You measure foot candles (fc) at 1 foot. To measure lux you go to 1 meter. To check your meter for consistency 1 fc (at 1 foot) = 1 lux (at 1 meter).
Remember that you are reading the brightest area of the hot spot to compare your reading with listed readings. You can also measure the spill light and form a ratio of hot spot to fill to further describe the beam from a flashlight.
The numbers are the scale for the reading. If you want to read 150 fc (or lux), you can use any scale. If you want to read 10000 fc (or lux), you can not use the 200 or 2000 scale.
To convert from fc to lux, 1 fc = 10.764 lux.
To convert from lux to fc, 1 lux = 0.0929 fc.
To obtain the light output at the source we refer to candela (cd). LED output is quite often specified in millicandela (mcd). mcd = cd X 1000. For example Craig has the Dorcy 1 LED flashlight output listed at 21600 mcd. This equals 21.6 cd.
Doug (Quickbeam) has excellent charts showing the relative throw of the lights he has reviewed. His throw figures are obtained from the Lux output of the beam factored by the inverse square law. If you take the square root of the Lux reading, you will get the distance in meters that the light beam will throw when the reading drops to 1 Lux. If you use fc, the square root of fc will give you the distance in feet that the light will throw with the reading dropping to 1 fc.
If you measure the light from a flashlight outside of the "standard" distance of 1 foot for fc and 1 meter for lux, you can use the following formula to compare readings:
cd = fc * feet squared or
cd = lux * meters squared.
Hope this helps.
Tom
Edit to correct formula - sorry.
