Integrating sphere's generally are used (in plant light measurements) for PPF (Photosynthetic Photon Flux) or in other words, the total amount of photons, that drive photosynthesis (generally between 400-700nm, but sometimes some meters expand the range from 380nm to 750nm)a light source will put out, every second... This is useful for determining a light's efficiency where you typically will see numbers like 2umol/joule which is telling you at a given wattage, how many total photos are output, every second. PPF is not as useful for direct plant to light measurements but more useful when chosing one light over another, and with HID/HPS bulbs and reflectors its very common to use to compare.I'm wondering... Does using an integrating sphere - while such a device is of course capable of capturing every photon emitted by a lighting device and, thus, able to show exactly how much light energy the products produce... If this rather expensive piece of kit doesn't end up sort of understating the power of those products? I am not feeling especially "word-proficient" right now (obviously, sine that isn't one), so this might not translate very well. But:
Integrating spheres also are useful for using spectrometers to determine the spectoral output of a light without having any secondary light influence on the measurements. I would say that they probably account for 98% of the light output as there is most likely a tiny percent of light that instead of being reflected is absorbed by the sphere and results in heat... so the readings probably are slightly less than actual, but I would assume with expensive equipment like that, they probably are calibrated for the loss too. Never used one myself.
The grids we commonly see are measuring PPFD or Photosythetic photon flux density which measures how many photons are hitting a single point on the ground, every second. Although PPFD is an "average over a square meter reading" by using the charts it is useful to map PPFD so a grower can plan to have an even footprint and properly illuminate their grow area based on a plants DLI or daily light integral.
Most LED companies and personal growers measure PPFD using handheld "PAR" meters and take spot readings, such as you may have seen on my old grow videos and light review videos on the youTub3. The fancy companies with a lot of research funding use what are called goniophotometers which are mechanical/robotic devices which measure light hitting a point at different angles and are the most precise way to plot out a lights pattern of diffusion "footprint". PPFD is typically what most agriculture operations use to determine if plants are getting the right amount of light at the canopy, and many times intracanopy. PAR meters hooked to dataloggers will be placed throughout large agriculture greenhouses to that they can track shading from clouds, and determine what supplemental lighting is needed.
anyhow, thought I would throw out a few lighting terms to help shed light on the differences of the two measurements and add to the convo as well
