i wanna talk about par or photosynthetic photon flux or PPF
come on now don't zone out stay with me people seriously if your eyes glaze over at
the mere mention of photons micro moles lux lumens and wavelength and nanometers then don't
worry
I feel your pain consider this quick presentation a sort of anesthetic
really I'm going to explain what PAR is why it's important to growers
and also why it isn't the be-all end all plant lighting measurement that some
folks might have you think it is
Buckle up amigos, this is going to be quite a ride
Sure lots of us are talking about par or photo synthetically active radiation like it's
our new best friend
but for those of you who aren't, PAR is simply a measure of light intensity for
plants. Maybe like me you've gone on bought yourself up a PAR meter
good for you this is basically a photon counter counting photons as they arrive
on its sensor a bit like the big bouncer dude who clicks his pocket clicker for
every person he lets into the club photons in case you're wondering are
just discrete packets of energy carried along electromagnetic waves
you can x-ray photons infrared photons even radio photons but PAR like
our beloved bouncer dude
is very selective just as he won't count you in for wearing those vintage adidas
sneakers
(Nice!) a par meter only counts photons traveling at certain wavelengths
typically between 400 and 700 nm this is the band of radiation
that both the human eye can see
and plants are able to use to fix carbon dioxide from the air
and bind it with water in order to produce glucose and oxygen
a process known as ... photosynthesis
of you were ahead of me there weren't you? So like I already said par stands for
photosynthetically active radiation
some botanists use this synonymous term photosynthetic photon flux
because it sounds even cooler kids especially that
flux part like a flux capacitor which is just a Marty McFly way of saying flow
I mean we're essentially measuring the flow of photons holding the sensor by a leaf in
order to ascertain
what that leaf is potentially absorbing okay time to throw curve ball at you
not all PAR meters are equal some like the Sun Systems par meter measure
everything between 400 and 700 nanometers
other meters and grow light manufactures count everything between 315
815 nanometers so if you compare two different lamps rated power output be
sure they're using this same range
so is more par actually better? Well yes
and no. First and foremost any grow lamp worth your hard-earned dollars needs to
be efficient at turning electricity into plant
usable light so you could be forgiven (I forgive you) for thinking that more par
equals a better growing light but alas
not quite that simple. Around 400 to 500 nanometers where radiation becomes visible
to the human eye
as a violet and blue photons carry more energy. At 600 to 700 nanometers the
orange and red part of the spectrum
photons have around half that energy basically
blue carries more punch than red but here's the thing:
your part meter doesn't care it simply counts all photons equal blue or red
whatever
as long as it's in range it counts each photon as the same
think of our bouncer friend again clicking each person into the club but
not bothering to record the ratio of dudes to chicks. Uh oh!
Sausage fest! We are nearly done I just wanna underline the fact that it takes more
electricity to produce blue light than red light so I could theoretically make a
high intensity discharge girl lamp with the arc tube packed full of extra sodium in
order to generate lots of cheap
low energy orange and red photons and Hey—I have a super high par lamp!
but will the plants grow better? No! That's because plants require a broad
spectrum of light in order to grow healthily
not an orange and red photon sausage party
okay check out these two graphs they show the spectral distribution of grow lamps a
standard 1000 watt metal halide lamp and a 1000 watt
enhanced blue metal halide lamp both manufactured by EYE Hortilux
judging from these graphs which lamp do you think has the most PAR the top graph
right?
Wrong! The standard metal halide lamp represented by the lower graph actually
has forty percent more PAR than the enhanced blue metal halide
probably do that and massive peak around six hundred nanometers
notice how the lower graph is actually a lot more spiky too
where as the enhanced blue lamp produces a fuller better-quality spectrum which
grows far healthier more compact plants with tighter internodes
okay so what did we learn? PAR measures light intensity for plants but
it does
not tell us very much it anything about the quality of the spectrum
it's very useful but growers should be aware of its inherent limitations
I did mention ppfd a way of measuring par that accounts for the reflector and
I will definitely save something called YPF
or yield photon flux for next time too--
a method of weighting each photon according to its absorption rate instead the
coating them all is equal—oooh!
but for now that'll do questions and comments below as always let me know if
you enjoy this video or if I sounded like Charlie Brown's teacher on a rainy
Monday morning mwah, mwah, mwah, mwah-mwah-mwah, mwah, mwah.
if the former hit that subscribe button in send me some photons
LOVE
if the latter then well done for toughing it out this far
see you again soon this is Everest OUT!