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!
 
