For indoor grows, which works better for reflecting light: Mylar or white paint?
What do you use and why? Any pros/cons of using one over the other? Do you use something other than white paint or mylar?
Would love to hear comments and or see any articles that provide info to back up opinions.
White paint - cause it was cheaper.
Now I use a mix of both depending on the space. The insulated mylar can be very useful for heat management. I have experimented with light reflecting collars - basically mylar pot covers at the base - reflecting light back up into the lower canopy. Maybe the lower buds were a bit better - but I donât know. It was a totally unscientific test.
Im going with white paint on my concrete flooring, and I have white backed vapor barrier insulation in my building. I dont have factual info but I dont believe mylar films have huge performance gains in reflectivity. Just my opinion.
While not necessarily âindoorâ - we also use a reflective insulated mylar on the north walls of our greenhouses to reflect light back down into the garden beds, especially in the Spring and Fall when the sun is lower.
I usually go with highly reflective eggshell white antiseptic, antimocrobial fda approved paints on walls. Usually these are the same paint hospitals use.
However painted white floors initially look clean they can be really difficult to keep looking clean and are hard on the eyes for workers
Dolphin grey antimicrobial epoxy flooring when done correctly with cove bases can be one of the best flooring solutions.
Im throwing a link up for everyone to check out. The product is called Tetramatch and if youâre doing a new build out or have plans on repainting your room I suggest this paint. It was created for hospitals and operating rooms and It reflects UV light and is antimicrobial. Check the link if you guys want more information. Also as for floors I prefer grey epoxy like @skye mentioned.Just get a 2 part with sealer and lay down multiple coats after its dried and sealed it will last years. Hope this helps out a bit.
Tetramatch Horticulture paint
Tetramatch Coatings for Indoor Horticulture â Twilight Coatings
From a lighting point of view: Reflective material has a huge influence on the light levels and uniformity of lighting of the room. The smaller the room, the bigger the influence. I can explain the latter with a simple ratio (and apologies for the metrics in here):
a 1x1m small tent has 4x1m walls: Ratio space to wall is 1:4
a 2x2m room hast 4x2m walls: Ratio space to wall is 1:2
a 10x10m room has 4x10m walls: Ratio space to wall is 2.5:1
In a small room the wall losses can be as high as 30-35% easily. Specifically because most small rooms/tents are square and almost all HPS fixtures have a rectangular throw.
Now LEDs with a limited spread have an advantage of not lighting the walls too much in a room, but you need much more distance to the crop to get an even lighting.
We recommend to always use Orca film or compatible products. In a small room that saves you even up to 20% of light in your room, in a large room the percentage is lower but the quantity of light you save is much higher.
As for uniformity it allows 5-20% better uniformity of light in a room.
White paint has a reflectivity of maximum about 83% (unless you use the super expensive Barium paint that we use in our Ulbricht sphere, which is 97), Orca does 95/96%. It is a great investment and you will actually see the difference.
I think Orca Film has the best reflectance across the spectrum, but after a bit of research white paint is quite similar at 1/4 the price. Hanging Orca is much faster, but paint will still be more economical.
Behr Ultra Pure White Zero VOC flat paint will cover 250-400sqft per gallon and is has a LRV (light reflectance value) of 94. Sherwin Williams High Reflectance White has a LRV of 93. LRV pertains to visible light and when I was geeking out on this I couldnât find a manufacturer who could provide a reflectance analysis over wavelength. I did find a white paper regarding adding barium sulfate to increase reflectance (anyone want to start a horticulture paint business?).
Zero VOC is much preferred, as VOCs can slow plant growth and create indoor air quality concerns in rooms with little air exchange. A paint containing fungicide must be avoided as they impact beneficial fungi and can show up on pesticide residue tests.
I hadnât heard of Tetramatch before reading this thread. I included their chart for comparison.
@jaya another white paper from Bruce Bugbee! We need to get him in Growers Network 
I think @Hunter might have a Growers Spotlight interview with him sometime the next couple months.
How did you get.measure this reflectance? Itâs quite different from the results we saw with white paint in experiments, and what we use in photometric calculation tools, based on average values.
The paint manufacturer provides LRV specs. This pertains to visible light, not necessarily the PAR range. 
ah, well that could be the key. In all our PAR measurents and specs we could not get above about 83-84% based on PAR spectrum. So that is still a significant difference with Orca. Even 5% difference would already reduce the efficiency in a room significantly. I personally believe the investment in a bit higher quality products easily weighs up against the extra light levels, uniformity and yield. Be well aware that you need to take the spectrum of your lamp into account when defining the reflectiveness. A large dip in red for example will totally change the average reflectiveness for HPS.
Here are two calculations of a room, one with 84% white paint, one with Orca. You can clearly see the huge influence of the better reflecting walls in the average light levels.
Please note that the colors represent DIFFERENT scales.
You can interpolate what 90% (or 5% less reflectance) would cost you in light.
I have to wonder â has anybody tried to use mirrors? And how practical would it be?
I have not tried it, but I have read that you lose light when it passes through the glass before it is reflected.
Thank you everyone! I am impressed with everyoneâs participation. Much appreciated!!
yes, we have used mirrors. Works great! Itâs only kinda impractical. Unlike what some people say (âyou will have hotspotsâ) specifically in small rooms it adds a lot of light. The light from your lamps and reflector is already sort of diffuse, so that will not be the case.
We experimented with several types of mirror material, glass mirrors have the disadvantage that you have to go through the glass twice. Material with a damped on reflective coating is hard to maintain.
that Tetramatch looks interesting btw.
I want to bump this up.
I will pull a study from penn state. Though, I think it may be from mushroom production publication.
It deals more with the problem with the carriers used in the paints can cause plant toxicity. This is very true in matalic colored paints(silver reflective) One glasshouse, I know of from first hand experience was forced to replace all of the hot water heating pipes. The carrier used in the paint is also used in some epoxy floor coatings. Greenhouse growers magazines had a story from the late 1980âs on not using them on heated flood floors. A grower in St. Louis had to sand blast 40k feet of brand new flood floors after loosing an entire poinsettias crop as soon as the heat was turned on.
We used foil covered insulation board in our germination room, it reflected very well. We also used electrical conduit as shelving for our plug trays. We could get about 100 plug trays on a 2 w by 10 l by 8.5 h. The biggest problem at the time was heat disapation.
