Maximum Yield Australia/New Zealand May/June 2019 | Page 76

PAR, PPF, PPFD
“With light movers, the grow
lights can be positioned much
closer and they can cover about
30 per cent more area —
and that’s per grow light.”
Fig. b
Fig. c
Light movement ensures more of the leaf surface
interacts with the grow light. This mimics how
plants naturally receive light (Fig. b). This reduces
shadow patterns and hot spots associated with
stationary lights (Fig. c).
PAR is the wavelength of light in the range of
400-700 nanometers and this is the range for photo-
synthesis. For the acronym components, it is photosynthetic
active radiation which is important in a conceptual way,
but it is without true measurement because it lacks time
and space. We can, however, dilute it with distance from
the light source, or we can concentrate it by positioning the
light source closer. That’s an example of Inverse Square
Law which is also highlighted in the PPFD chart, with the
PPFD numbers hugely diminished, and that’s geometrically
diminished, with distance. Photosynthetic photon flux
gives one more piece of information for PAR, which is time.
We can see photon output per second. A quality grow light
emits a continuous strong output, and PPF tells that story.
The measurement is micromoles per second (μmol/s). The
best grow light number to know, however, is PPFD because
it incorporates space and time into the calculation.
Basically, it is PPF plus micromoles per metre. It is the
measurement of PPFD. Photosynthetic photon flux density
readings must be done properly and include distance
to grow light, horizontal coverage, and the number of
readings taken over a period of time. For the PPFD chart,
the distance and the horizontal coverage are listed. For
other needed information, the meter took a reading every
30 seconds, so 120 readings per hour and every 30 minutes,
calculated for the average, and that was per area.
Photon efficiency: This is all about how efficient a grow
light is in converting electricity into PAR. It’s important
to know because we are not just thinking of electrical
input but are now having the added information of real-
ized output. For the math and knowing PPF (µmol/s) plus
knowing wattage (Joules or J/s), the formula is µmol/J
because the “s” for seconds cancels out on both sides of
the equation. The higher this number, the more energy
efficient a grow light is at converting electricity, which is
input, into photons of PAR, which is output.
The two most important grow light numbers to know are
PPFD and photon efficiency. A quality grow light will be
outstanding for PPFD and should be noticeably better
than most for photon efficiency. Then, placing that grow
light on a light mover and getting it closer than would be
recommended in a stationary setting is ideal for opti-
mized results. This is how to best maximise PPFD with
stronger/better coverage while creating better efficiency
than with a stationary grow light. And, that’s by covering
30 per cent more area as a moving grow light.
Grow lights can be powerfully effective while being
energy efficient, and light movers are the single best
way to maximise this. So, know a grow light’s PPFD,
know the photon efficiency and, just as importantly,
know the possibility of those grow light numbers when
maximised on light movers.
74
Maximum Yield