I installed an app on my smartphone that uses the screen sensor to measure the lux of a room.
STUPID
QUESTIONS:
1 - Is it possible to use this to measure lumens, candelas, and the output of a flashlight?
2 - How do I take these measurements?
I imagine the result is more reliable than the information from flashlights with one XML LED and 9,000,000 lumens
Continuing the discussion from The There Are No Stupid Questions Thread:
No
Yes
What is “output” ? Lumens IS a flashlight’s output.
You should shine on your phone from a known distance, let’s say 5 meters. By multiplying the phone’s lux readings by the square of the distance you’ll get candela. The beam should arrive to the surface of the phone perpendicularly and no reflections from nearby objects are welcome.
Precision of this method is probably low.
I use this website to convert lux to candela.
It’s advisible to use a flashlight with known candela as reference. So you divide the measured candela by the theoretical to get the calibration factor.
For lumens, I use the ceiling bounce method. Just point a flashlight with known lumens to your white ceiling, do the same with the unknown flashlight at the same position and compare lux from both. Not very precise tho.
Yeah, issue is that different phones may have different calibrations and response curves (i.e., reading not scaling linearly during a linear increase of intensity).
What is always feasible and useful, though, are relative measurements. If you assume monotonicity, then if one light reads more intense than another, it probably is. If you assume a linear response curve, then if one light reads x% more intense than another, it probably is.
To get the total lumens is more difficult–you need to build an “integrating sphere” that smoothes the beam into a uniform distribution on a sphere, where the intensity reading at any point is representative of the total output.
But if your lights have a similar beam profile, simply bouncing the light off a white ceiling would do. This ceiling bounce method will give you relative output, and you would need to find a universal constant of proportionality to scale them into actual lumens. A well-regulated, medium-output light with a trustworthy output rating is usually used for this determination.
Sorry. I don’t speak English and I rely 1000% on Google Translate.
I want to find these three items in the example:
Lumintop Moonbox 3.0
1200 lm / 3125 cd / 112 m
Lumens/Candela/Distance
thanks for the tip
If you’re interested, I highly recommend trying translation by ChatGPT. I’ve found it to have a much better understanding of contextual meaning and syntactical logic, compared to Google Translate.
Also, please feel free to include your original text in Portuguese, in addition to the translated text. Some of us might have an easier time understanding Portuguese than computer-translated English.
Lately I suspect a few Dutch translators who supply subtitles for English spoken movies and documentaries of using Google translate. Well, a good laugh or two is like ten minutes in the Gym. Because a lot of those translators are not taking the time to check how far off their output actually is.