Photon efficiency and cost per mole of photons, assuming all photons (180°) are captured by plants.

z- See Table S1 for a list of fixture manufacturers and model numbers.
y- Integrated total photon output of fixture.
x- Photon Output per Electrical Input (µmol per second divided by joules per second).
w-Cost of fixtures as of April 2014.
v-The number of fixtures to get a total photon output of one millimol (1000 µmol) of photons per second.
u-Assumes 3000 hours per year operation and $0.11/kWh.
t-Cost of fixture (multiplied by fixtures needed) plus cost of electricity over 5 years. We used a discounted cash flow model assuming a 5% per year cost of capital. Installation and maintenance costs were assumed to be similar for all lamp types and were not included in this calculation.