Answering the second part of the question...

FvP / FmP = (FmP - Fo) / FmP - efficiency of open reactions centers in the light. Phi2 = (FmP - Fs) / FmP = ΔF / FmP - quantum yield

Hi Weizhen Liu, Both parameters, NPQ and PhiNPQ, are related with non-photochemical energy dissipation, actually, NPQ means Non-Photochemical Quenching. So they are related to dissipative mechanisms that plants use to cope with the extra energy absorbed by the PSII complex. PhiNPQ is an energy partitioning parameter that indicates how much energy if been dissipated by regulated non-photochemical quenching. This parameter is related with Phi2 (the PSII quantum yield) and PhiNO, the quantum yield of non-regulated NPQ processes. Please find a complete explanation in Kramer et al 2004 (Photosynthesis Research 79: 209–218, 2004). The thing is that they give you different information about related processes, I mean both refer to non-photochemical dissipation but the first is more general and the second is telling you how much of the energy absorbed is been dissipated by regulated NPQ (YNPQ), so you can related with energy losses by non-regulated mechanisms (YNO) and energy used for photochemistry (YII). But, I insist, for a complete description go to the Kramer’s paper. For all these parameters you need the Fm determination, so plants must be dark adapted (at least 20 minutes). Tietz et al. 2017 developed an approach to overcome this necessity, using some assumptions, allowing the calculation of NPQ (called NPQ(T) in the paper) and the other parameters (PhiNO and PhiNPQ), without dark adaptation. In summary, no parameter is better or more accurate than the other, they just give you different information. The PhotosynQ protocol use the Tietz approach, so you can have reliable values directly from plants in the field without dark adaptation. About the second part of your post, I agree with Andriy and Nataliia. I just add that you can think this value as a maximal quantum yield of PSII under light conditions. It’s related with maximal quantum yield of PSII: Fv/Fm parameter (= (Fm-F0)/Fm , this also need dark adaptation) but the equation for FvP/FmP is (Fm’-F0’)/Fm’. The p means the ‘ symbol, which is used to indicate fluorescence values taken under light conditions (remember that Fm and F0 are taken on dark adapted leaves). Well, I hope you find this useful. Good Luck! Rodrigo