I ran a test on the Acebeam K65. First I fully recharged the bats and put them in the K65. Then I stood it up to shine on the ceiling in my room. Set up the online stop watch. I started the cam on my phone and started the test.
After 5 minutes I saw no changes and it almost burned my finger when I went to turn the light off. I ran the playback and skipped to the 4 min mark and back and saw no difference in brightness or intensity.
Should it be noticeable? I have a feeling that it just maxed out to 4000 lumen and that's it.
If it’s in auto mode, your camera/video recorder will continuously adjust brightness based on the amount of light that’s available, so you can’t rely on it to do a test like this.
If you have a fully manual camera, you could set it to the exact same shutter speed, aperture, and ISO level, and then take two pictures - one at the beginning and one at the end of the test. Even then, it may have difficulty capturing super bright objects.
If you have an Android smartphone, you could try using the ceilingbounce app in a shoebox:
Otherwise, just get a light meter. To the naked eye, there isn’t a ton of difference between 6200 and 4000 lumen.