Tried measuring my flashlight withthe light sensor on Galaxy note

[tsk1979]

I have a flashlight I bought off the street in Thailand. It says Ultrafire JK-123 or something like that.
I feel its fairly bright.
So I switched off the lights at night, and my phone light sensor was showing 0.00 lux.
Then I shone the flash light at the phone from a distance of 10cm, and it said 17000 lux. I figure the square meter area where the main beam was concentrated was probably only 25cm^2 = 0.0025cm^2. So the lumen output can be safely said to be approx 40 lumens?

 

[TEEJ]

I have a flashlight I bought off the street in Thailand. It says Ultrafire JK-123 or something like that.
I feel its fairly bright.
So I switched off the lights at night, and my phone light sensor was showing 0.00 lux.
Then I shone the flash light at the phone from a distance of 10cm, and it said 17000 lux. I figure the square meter area where the main beam was concentrated was probably only 25cm^2 = 0.0025cm^2. So the lumen output can be safely said to be approx 40 lumens?

10 cm is awfully close to measure lux at.

25cm^2 ≠ 0.0025cm^2 though (Typo?)

= 0.0025 m^2 would be correct though.

Your calculation assumes that ALL of the lumens were turned into lux, and, typically, that's not the case.

If it were, you'd have a light that hit 170 lux at one meter, not too impressive.