30 watts a foot,
thank you for the comment. Thank you for the compliment.
Ya, 30W/ft2 - 35W/ft2 for mid to high efficiency LED (2.35μmol/J - 2.7μmol/J), I'm not sure if you were asking for confirmation or not.
1m2 = 10.764ft2
1W = 1J/s
Lets say your LED pushes ~2.5μmol/J.
2.5μmol/J × (10.76ft2/m2) × [(30J/s)/ft2]
=
807μmol/s·m2
If your fixture is 2.1μmol/J, and your target PPFD is 850μmol/s·m2 then...
(850μmol/s·m2) = (2.1μmols/J) × (10.764ft2/m2) × [(θJ/s)/ft2]
(850μmol/s·m2) ÷ (22.604μmol·ft2/J·m2)
=
[(θJ/s)/ft2]
θJ/s = 37.6W
Walls ect will absorb some of the photons emitted, and if the spread or throw of your trajectory is greater than 1ft2, then youll have to add more wattage to achieve whatever per ft2 intensity you desire.
After further review of your light I'd estimate an efficiency of ~1.5μmol/J. The luminous efficacy of emission of a typical 5000k 80CRI SPD is somewhere around 310lm/W (max lumens per watt, or 100% efficiency). The datasheet linked shows a CRI of 67, so its luminous efficacy of emission is probably closer to 300lm/W (less diverse SPD, SPD is more clumped around base pump of ~450nm which is less observable to the human eye than a higher CRI SPD). The data sheet shows 98lm/W as the highest performing model in the 5000K category. A typical radiometric efficacy of the emission of a 5000K SPD is ~4.55μmol/J, perhaps a bit less considering lower CRI than the one I'm modeling after (a 80 CRI, max μmol/J or 100% efficiency).
(98lm/W) ÷ (~300lm/W)
=
0.326 electrically efficient
0.326 × (~4.5μmol/J)
=
1.47μmol/J
So...
(416W) × (1.47μmol/J)
=
611.5μmol/s
You'd want to divide the surface area that the throw of your light creates by ~610μmol/s to calculate your canopy PPFD, at least concerning the street light. Lets say you hang it to the point that your throw is 4ft2.
(610μmol/s) ÷ (4ft2)
=
152.88μmol/s·ft2
10.764ft2 = 1m2 so...
(152.88μmol/s·ft2) × (10.76ft2/m2)
=
1644.98; 1,645μmol/s·m2;
1,645PPFD
That's quite a bit of blue light and not a very diverse SPD without supplementing with your clamp-on's. I'd recommend hanging the street light so that it provides a throw of ~12ft2 (548PPFD) and then add some 3000K 90CRI bulbs for the clamp-on's (enough for 300 - 350PPFD more, for a total of 850 - 900PPFD).
You can estimate your clamp ons in the same manner but use 340lm/W as the luminous efficacy of emission for a 3000k 90CRI bulb, and 4.8μmol/J as the radiometric efficacy of a 3000K 90CRI emmision. They won't be exact figures but will give you an idea of the wattage per bulb you'd want to buy/use, how many of them, and how high to hang in order to blend your ratio to your desired level.
Also you can buy a cheap light meter to estimate intensity or PPFD from. They are sensative to a limited spectra so they'll measure certain SPDs with more intensity than others and are not exact but they can give a, "this spot is brighter than this spot" type of indication. The measurements may resemble true intensity, or they may not, it just depends on the SPD of emission and the spectral response of the instrument. Price will likely scale with accuracy.
EDIT:
The calcs are averages, so you'll still have greater intensity directly under than at the edges, so if you're not reflecting the side emmisions back in you may want to further increase your hang height to account. If you're good with trig you can calculate an estimate based off the beam angle found on the data sheets, sometimes they're listed as radiance, or in units of output power per steradians per m2.
