Grow lights are different to normal household light bulbs, they provide light to plants that is in a different wavelength than the light which we can see (or the visible light spectrum). To understand grow light measurement you first need to know the difference between the main measurements:
Lumens - Spectrum of light that fits in the wavelength that the human eye can see.
Watts - purely a measure of energy consumption.
Kelvin - measure of "temperature" of light for example blueish or reddish light
PAR - Photosynthetic active radiation, the wavelength of light that plants need to grow.
PPFD - Photon Photosynthetic flux density, or the intensity of light produced in the spectrum required for plant growth.