I have an Urceri lux meter from Amazon ($29.99).
I have had zero luck with apps and Android based phones. I have compared 3 different apps, on 3 different devices, that's a total of 9 different combinations, versus my lux meter and found wildly varying results. Zero stars, would not recommend. I've seen other tests that suggest Photone and Apple phones work well, but since I do not own an Apple phone, I cannot verify that statement.
I'm not up to speed on the lux to ppfd relationship so I sought out the help of an online
Calculator. I put in 35,000 lux and selected Red+Blue+White LED as the closest approximation of my light and got a result of 899. Is that right? I have no clue. I've always delt in lux since true PAR meters cost many times more than a lux meter, and I've used my meter in conjunction with Royal Queen Seeds "How to use a lux meter" suggestions.
For what it's worth, ViparSpectra says that at 100% power and 12" hanging height, the center of the tent should be approximately 1000 ppfd for the KS3000. I'm at 100% power and about 18” so maybe the 899 ppfd computation above is in the ballpark. They have 75% and 24" height as 600 ppfd.