- That's right: you're losing over a third of the PAR
in the back of your aquarium,
simply because you painted it black.
But how and why does that happen?
Does the same loss of PAR happen
if you paint the back of the tank white
or blue or light blue.
Or what about a mirrored look?
This little laser is going to tell us all of the answers
in today's BRStv Investigates.
(fast rhythmic music)
I've personally tested the PAR output
for well over 50 aquarium lighting options,
and in each test, we always see a band of lower PAR numbers
across the back of our tank,
which, of course, happens to be painted black.
Not only is it noticeable at the top of the tank,
just six inches below the top of the water,
but it's even more prominent the further down you go.
In an effort to make sure
that our light testing procedure is correct
and that we are providing you with the most accurate data
for you to apply to your own tank,
we thought it would be fun
to test out other painted background scenarios,
including no background at all, white,
three different shades of blue,
and even a mirrored paint surface.
What we're gonna learn about light reflection,
refraction, and the absorption of light
will open our eyes into a whole new world
of how our reef tank lights act inside the tank,
and it just might change the way
that everyone paints their tanks
from here on out.
All right, so before we get to the laser portion,
which has to be the coolest part of today's experiment,
we first need to test what is happening to the PAR
near the back of a painted tank,
and if the color choices make a difference.
The goal will be to measure the PAR
across 75 points in each tank
at the top, middle, and the bottom,
all of which using the exact same Kessil A360X
at the exact same eight-inch mounting height,
and then compare how much PAR is lost or gained
on that back wall.
We'll look at this PAR data from two angles.
First, how does the different painted colors or shades
affect the overall total average PAR
throughout the entire tank,
and second, is the loss of PAR more prominent
in that middle and bottom of the tank,
where a majority of your corals are placed?
Looking at the total average PAR first,
the difference between the higher-end glass
and mirrored-back tanks at 112,
versus the 101 PAR at the lower end on the black tank,
may not seem like much,
but in fact, that is a 10% loss altogether.
One of the more interesting things that I see
is just how high the clear non-painted tank is
and how it seemingly acts
just like a completely mirrored surface.
Another interesting result that caught my eye
was how the white
and the two lighter blue backgrounds performed.
Again, I would have thought that white
would probably have a higher average
since white reflects back all spectrum ranges,
while black absorbs them.
However, we see a slight decrease over the mirror
and the clear glass.
Now moving onto the comparison for PAR measurements
in the middle and bottom of each tank,
specifically, those back two rows of measurements
you see here, which always seem dim in our tests.
This is where we start to see
even more significant loss of PAR,
due to the color and shade differences,
where the clear non-painted tank
has the highest average of 115,
and the black has the lowest at 82,
meaning by painting the back of your tank black,
you could be losing upward of 28% of PAR.
So this might not be a major issue
for reefers who like that rock wall-looking aquascape
with all of the rocks piled up in the back.
However, for NSA aquascape or islands like the Brs 160,
all those corals in the back quarter of the tank
are now receiving less light than if they were in front.
So the results here are largely the same
as what we just saw in total average PAR
but more pronounced.
The clear and the mirror tanks are nearly identical,
while the white and two lighter shades of blue
are also very similar.
But why is that?
How could a non-painted tank
reflect even more light back inside,
versus a solid mirror?
And why did the white,
which reflects all of the light spectrum,
lose 19% average PAR over a clear tank?
Well, let's get the laser out
and see if we can answer those questions.
As you can see,
behind me are seven tanks
that are now filled with neon green dyed water.
And in just a second,
we're going to point this high-powered laser
inside at the back wall
to see what happens to that beam of light inside the tank.
Keep on the lookout for any changes
to the intensity of the laser beam
as it bounces from the back wall down to the bottom
and back to the front,
which will give you some insight
as to which colors or shades are reflecting,
which are absorbing, and which are scattering the beam.
All right, first let's check out
the unpainted versus black tank,
which were at the extreme ends of the PAR testing
that we just finished.
Immediately, you can see
just how strong that reflected beam is in the clear tank
versus how dim it is in the black tank
after it hits the painted back.
Not surprising here
since we know that black absorbs light spectrum.
However, there is still a faint reflection
off the back wall,
which is likely more from the inside of the glass
versus the outside.
Now check out the unpainted tank
and the white tank side by side.
Again, the reflected beam off the white background
is definitely less intense than the clear tank.
However, notice the halo around the laser beam
on the back of the white tank.
What we're seeing here firsthand
is the difference between diffuse reflection
and specular reflection.
So it's true that white does reflect
all the light spectrum ranges.
However, instead of a mirror
that redirects a beam of light
at the same angle of incidence from the source,
a.k.a. specular reflection,
the white surface reflects the source of light
in all kinds of directions,
which is known as diffuse reflection.
This is why you see that halo on the back of the white tank
and not on the clear.
And you can also see the same diffuse reflection
on the two lighter shades of blue
that were nearly identical in PAR to that white tank.
So that brings up a good question:
How many white or light blue tanks
have you seen painted in the hobby?
Personally, I haven't seen very many,
and that's probably due to how hard it is
to stay looking clean with a white surface on the back.
So that leaves us with two choices: either clear or black,
which is the most prominent in the hobby.
So, for me, it's just gonna come down to the aquascape.
If I have a stack of rocks on the back of the wall,
this does not matter.
However, if I'm thinking about an NSA aquascape
or some islands
where I plan on putting corals near the back,
I just might consider going clear,
and if I don't like it,
I can always paint the back black later.
So the question still lingers
of why the clear unpainted tank performed
even better than a mirror or any other tank we saw today.
It also raises the question of,
have we been misled about our light's actual PAR output
from somebody who tested it wrong
and may have shared the wrong info?
Well, Ryan's got the answer to those questions
in this BRStv experiment, right over here.