PPFD is photons per area per second. So the measurement obviously changes according to distance. 5cm away you might catch all the photons, 10cm away, you'll catch 1/4 as many photons, etc, etc. because of the inverse square power law.
So what distance are people supposed to measure their PPFD from? Is there a standard distance? It's very confusing to me when PPFD measurements are given without a distance.
So what distance are people supposed to measure their PPFD from? Is there a standard distance? It's very confusing to me when PPFD measurements are given without a distance.