Need a PAR reading?
I love BRS but they no longer rent out PAR meters for $70. Now you purchase and return them with an $80 stocking fee. Not bad, and I don't blame them for not wanting to be in the rental business, it seems like it would be a PIA.
Here's another option...
I have zero ties to this company but they could be quite good for reefers? They have a PAR meter app that supposedly only deviated 5-7% from an Apogee SQ-520.
The entire reef ecosystem depends on light for photosynthesis, which is measured as photosynthetically active radiation (PAR). But without correction, PAR meters calibrated in air provide only relative values underwater. This article explains how to take accurate PAR measurements underwater.
The grow light meter app to measure PAR / PPFD, DLI, lux / fc, or Kelvin with your iOS or Android phone. Including PPFD meter and DLI conversion for plants.
growlightmeter.com
It does need a homemade white paper filter/diffuser.