I'm not sure a lux meter is really what you want for accuracy. Does it do other functions like Par readings? From what I remember it's not really applicable to usable par/pur it's more just for brightness. I've used mine ( phone) in a bare tank and it didn't relate to the apogee par readings whatsoever. Maybe there's a conversion or something or developments I don't know about but from what I remember it's basically useless..
And FYI most Android phones ( maybe Apple as well not sure) have a built in lux meter you can get to going into developer mode for free
Would should the peak lighting be at?
It's at 174 at the x100 and 200,000 setting right now
Deciding on a lux level is similar to deciding on Par level. youll have to do some research.
According to Apogee and D riddle there are some easy conversion numbers.
The sun is 53(I use 50 just for ease)
bluer Mh and T5 seem to fall in the 50 conversion as well
t5 and some MH in the 10,to 14k range run in the 40 range
From My and D riddle I have observed LED to be 60.
So
warm T5 Mh 40
Blue MH t5 sun 50
Led 60
So if Daniel has 18,000 lux on his led, divide by 60 300 par.
I have on my 55g, 40,000 lux so 600 par.
If i have a question on it I run the same number 40k / 50, or 40k by 55. its usually in the ball park
I personally have not yet seen an led that gets better than 60 as a conversion number.(save "white" only but nothing conclusive)