I had been unaware of measurement according to "moles of photons", though I suppose it's not surprising. I've never really understood what a mole is other than "we decided to pick this number as a constant multiplier when doing small calculations".

Per wikipedia[0], there's a vaguely defined unit, the Einstein, which may be defined as the energy in a mole of photons. (The vague definition being because each photon may have different amounts of energy, and thus an Einstein would be some weird function in order to describe total energy.) Wikipedia suggests using measures of Photosynthetically Active Radiation (PAR)[1], like Photosynthetic photon flux (PPF) instead. I suppose this is because PAR is literally defined to measure according to "what plants crave", but it also allows bounding the "total joules of energy" above and below by the PAR wavelength limits.

[0] https://en.wikipedia.org/wiki/Einstein_(unit)

[1] https://en.wikipedia.org/wiki/Photosynthetically_active_radi...