I am trying to determine the PPFD of rooftops and walls by simulation in order to study the placement of rooftop and wall plantings. I was wondering if it would be possible to obtain solar radiation and convert it to PPFD, but I have not been able to find any references. If anyone has any references or findings, could you please share them?
Please note that the analysis surface may be in the shade (no direct sunlight) as the surrounding buildings are input into the model for the simulation.

PPFD (Photosynthetic Photon Flux Density) is a metric used to measure the efficiency of photosynthesis. It represents the amount of energy from light within a specific range that is provided to a given area, typically measured in square meters.
Typically, PPFD is expressed in units of μmol/(m²·s), representing the number of photons (amount of light energy) per square meter per second.

We’ve done some studies with PPFD in the past with the assumption that it’s pretty much directly related to the solar irradiance (W/m2). So you can essentially post-process the output of the HB Annual Irradiance component to get PPFD. The formulas we used came from here:

… and here is the rough sample code for converting irradiance into PPDF:

def calculate_ppfd(irr):
"""Calculate PPDF from irradiance.
Args:
irr: Irradiance value in W/m2
"""
daily_irr = 24 * irr # multiply by 24 to get the value for 24 hours
par_full_spectrum = daily_irr * 3600 / 10 ** 6 # value in MJ/m2-day
par_400_700 = par_full_spectrum * 43 / 100 # 43% of the spectrum
return par_400_700 * 127.79 # convert PAR to PPFD