Today I want to discuss determining your plants' light requirements, and supplying
it uniformly over a given area. Back in the day when indoor growers flowered
under HPS lights and batwing reflectors folks used to talk in terms of watts per
square foot. 50 was a number you heard banded around quite a lot as a general
guide for maintaining high light levels for flowering, and fruiting. With modern
HID lighting, you should take the total square footage of your garden and
multiply it by between 35 and 50. Obviously, lower numbers for more
efficient lighting fixtures. Example a 12 ft by 10 ft area, 120 square feet
will require between 4200 and 6,000 watts. How you divide
that into separate lighting fixtures 400 watt, 600 watt, 750 watt, 1000 watt, etc.
often comes down to the vertical space you have available for plant growth. The
type of reflectors you wish to use in the actual dimensions of your grow
space. But your first step: get to know your plants. They're the finest PAR
meters known to man, after all. What light intensity do they actually require? In
this example we'll shoot for moderately high, say 22.5 moles of
light per day. To make things interesting, let's say we need to deliver all this
light in a short 12 hour photo period. The math is straightforward: one mole
equals a million micro moles, so 22.5 moles of light per day equals 22,500,000.
The next step is divide this huge number by the number of
hours the lights will be on: in this case 12, and then divide the result by
60 squared, or 3600. This series of divisions takes us from moles per day, to
micro moles per second and voila! Our target light intensity is 521 micro moles,
ladies and gentlemen. This number is often referred
to as the target PPFD, or photosynthetic photon flux density. Basically, it's a
measure of plant usable light intensity that's actually hitting your plants'
leaves. Let's imagine that we want to achieve this intensity over a 69 square
foot area, or 6.6 square metres. This just so happens to be the measurement of my
basement, or rather, the part of it I want to actively grow in. It's high summer and
all this PPFD testing would be horribly hot in a sweaty task if it weren't for
my newly installed Khan Atom climate controller: a compact, grower-friendly,
reversible air conditioner. Thankfully, all testing will take place at a very
pleasant and consistent 72 degrees Fahrenheit, or around 22 degrees
Celsius. You're going to see my basement grow
room upgrades very soon, including a range of high-powered LED fixtures. Oh
yeah! But for now, back to our test. Note that the ceiling is just under
8 feet, or 240 centimeters. And as regulars to my channel will know: I've
tried 1000 watt double-ended fixtures in here, and even when using air cooled
hoods, vertical growing space quickly becomes an issue. That's a shame because
double-ended HPS is so efficient at creating plant-usable light. However, I
might have found salvation in the form of these Adjust-A-Wings "Hellion"
double-ended fixtures. They can run a double-ended HPS lamp at 450, 600, or 750
watts, and they're brand new to the market. I'm very excited to check
them out. Four 600 watt lights, or 750 watts, are a more natural fit for my
grow space. Basically, I've divided my area into four, and positioned each light
exactly in the center of each subsection. The Adjust-A-Wings' double parabolic
reflectors are incredibly good at creating uniform spreads of light, while
their shape helps to mitigate heat buildup inside the reflector. As the name
implies, you can also adjust the shape of the reflector on the fly so that it's
tailor-made for your grow space. Nice! My 5 by 5 movable test grid has holes
drilled every 112 millimeters, that's just under four and a half inches. Each
hole is just big enough for me to poke my Apogee MQ-500 quantum sensor
through. The rigid hole helps to ensure that the sensor is as close to 90
degrees as possible, relative to the test grid. Apogee quantum sensors are convex,
and stated to be cosine corrected, in an effort to improve the accuracy when
measuring scattered or angular light. It's worth noting that as the distance
between my light sensor and the actual light source increases, the angle of the
predominant light that strikes the sensor becomes more acute, and the
associated PPFD readings decrease surprisingly quickly. Further, if I tilt
the sensor to face the direction of the arc tube, the PPFD readings often increase,
and quite considerably in some cases. However, the standard procedure is to
keep the angle of the sensor at 90 degrees, pointed straight up at the
ceiling for all readings. This maintains consistency of experimental method, which
is all well and good, but I'd argue that my current methodology favors the design
of multi-point LED and T5 fixtures, where the light source is invariably directly
overhead. I'll discuss angular light and canopy penetration in more detail in an
upcoming video. The reflectors have been set to their second widest setting in
position 60 centimeters, that's just 2 feet, above the test panel, allowing for
the extra two centimeters that the quantum meter probe
pokes through. I measured the light intensity at 460 test
points across the 69 square feet, and here are the results.
Bam! Doesn't that look beautiful? I've got peaks of around 800 micro moles
right underneath each lamp, and lows of around 350 at the open side of my grow
space. If you compare this to the opposite side, which benefits from the
matte-white walls' reflectivity, you can get an idea of how much light you lose
to open spaces in your grow room. This is one main reason to fill the entire room
with plants. The intensity, overall however, is incredible. Check out how the
pattern is transformed when I add Super Spreaders beneath each lamp. Now, I'm
going to talk about these ingenious devices in more detail in a follow-up
video, but look how amazing they are diffusing those hot spots, and making the
light even more homogeneous. Another small anomaly I'd like to point out is
this little dim section right here. Right by the alcove, which is acting as a trap
for reflected light. No big deal, but interesting to see the physical quirks
of my grow space manifesting directly in the PPFD data. And just in case you were
wondering, this space is all being illuminated at just under 35 watts per
square foot. 2400 watts divided by 69 square feet. The efficiencies come from
the double-ended lamp, the reflector design, and the incredible Super
Spreaders, which permit a much closer hanging distance, while protecting plants
from the infrared overload. Obviously, the proof will be in the pudding, or
maybe in the spotted dick, or a toad in the hole, but for now I'll leave it there.
If you're looking for intensity but don't have 15 high-foot ceilings to play with,
I definitely recommend checking out the 450, 600, 750 watt double-ended systems
before you defaults to 1000 watts. I've included a link to a handy online
lighting planning tool in the description below. If you want me to drill down into
more examples, just let me know. There are so many variables that it's difficult to
cover everything in one video. Thank you for watching. This is Everest, always
intense, yet evenly distributed, saying goodbye.