[GWE] Reflection - Increase Yields w/ Reflective Walls


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May 15, 2014
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Introduction to Reflectivity
Introduction to reflectivity in the cannabis grow room
Indoor cannabis grow lights are bright, but you can make them seem brighter without actually changing the amount of electricity you use. Proper reflection of the walls near your cannabis plants, and a great hood/reflector will bounce the light from your indoor grow lights back at your plants instead of letting all the light that hits the sides be absorbed.

Proper reflection can get up to 30% more light to your cannabis plants! This is all without changing anything else about your setup. No extra electricity, but 30% more light!

As you probably know, light is what cannabis (and all plants) use to make energy and light is what powers the growth of your buds.

It's important to understand that indoor cannabis grow lights are most effective when they are close to your plants. The further your cannabis plants are from your grow lights, the more light that gets "lost" on the way. By making sure light is reflected back at your plants instead of being absorbed by the walls, your plants get to use more of the light that gets produced.

Reflective walls will also help prevent any part of your plants from sitting in a dark or shadowy spot.

More lights = faster growth & bigger yields!

Today I will guide you through the most effective ways to get more light to your cannabis via reflection!

The walls of your grow area:

To get the most reflectivity, you should keep walls as close to your cannabis plants as possible.

Your plants will get more light if they are in a contained space with reflective walls compared to plants sitting in the middle of an open room.

This is partly why grow tents and grow boxes are so effective - in addition to helping you provide the perfect environment to your plants, they help contain the light so your plants get more of it

Make sure reflective walls are set up to achieve the greatest reflectivity

No creases
Walls are completely flat with no bends or turns
Smooth curves are better than obvious bends
Reflective material is not dirty or discolored - keep your walls clean!
Avoid creases or bubbles in your mylar (or other reflective material) as it reduces light reflectivity
Note: When covering the walls with something that comes in a flat roll like mylar, foylon, or aluminum foil, make sure the material is placed flat against the wall to avoid air bubbles which can create hot spots and reduce the reflectivity. Velcro is a great way to place up reflective materials with minimal creasing or tearing.
Reflectivity Options For The Cannabis Grow Room

Different reflectivity options vary in their efficiency. It's important to find a solution that fits your setup and your budget. I will cover some of the most popular options, along with the pros and cons of each one, to help you pick the right option for your cannabis grow room.

Highly Recommended Reflectivity Options for Your Grow Area

Grow tent walls (best reflectivity)

Getting a grow tent will give cannabis growers the best light reflectivity of any option. Grow tent walls are easy to clean, light proof, water resistant, won't melt, and grow tents are created with built-in cooling options. When it comes to growing cannabis, grow tents are the best option for your grow area "walls" as they have been designed and engineered over several decades to create the best indoor grow environment for your plants. Grow tents can be found in any size, and generally will give you the best results for your money. After I got my first grow tent, I realized I could never go back to growing in anything else.

Cannabis grow tents have the best reflectivity options for your grow room
Flat white latex paint (85-95% light reflectivity)

This is a highly recommended option for those who can't invest in a grow tent and will give you some of the best "bang for your buck" of any reflection option. Flat white paint is inexpensive, effective, and there's no way to create air pockets or hot spots behind the reflective material. Just paint the walls, let them dry, and you're done....

White paint absorbs a lot of heat without reflecting it back into the room (which would require more venting to keep heat down) and painted walls are easy to clean. Do not get glossy paint - you want flat (matte) white paint for the greatest reflectivity. You can paint the floor and ceiling for even greater reflectivity. Sometimes paint containers will list the reflectivity, and the more reflectivity, the better.
Flat white latex is an easy, cheap and effective light reflection option for the cannabis grow room
Panda Plastic (85-95% light reflectivity)

Panda plastic (also known as "Black and White Polymer") gets its name from being white on one side and black on the other. Although a bit expensive, Panda plastic provides great light reflectivity. You point the white side towards the lights, and the black side will help trap light from getting in or out. Panda plastic can also be nailed or otherwise attached to your walls and is easily taken down. The thicker the panda plastic, the more durable it is. Remember, this is made of plastic, so it can melt if it gets too hot - be careful to never let Panda Plastic sit too close to your lights!

Panda plastic is a a great reflective option in the cannabis grow room
Orca Grow Film - (90-94% light reflectivity)

Orca grow film is made of white plastic microfiber and uses a unique structure that is similar to snowflakes or the skin of orcas (killer whales) to scatter light. Although expensive, Orca grow film is mold-resistant, easy to clean and thick - these features make it more durable and less likely to tear compared to some other reflectivity options. Using highly reflective crystalline structure, Orca grow film evenly distributes reflected light so it doesn't tend to create hot spots even when it has some creases. Orca grow film tends to reflect back infrared light as well, which means it will tend to keep heat in the grow room. Like Panda plastic, point the white side at your plants with the black side facing outwards.

Orca grow film is very reflective and great for the walls of the cannabis grow room
Good Reflectivity Options
Kool Seal White Elastomeric Roof Coating (90% reflectivity)
Kool Seal White Elastomeric Roof Coating forms a thick rubber-like reflective coating that i
Although very expensive (which is the biggest problem with this option), white elastomeric roof coating is a great option for some growers. Kool Seal White Elastomeric Roof Coating is made of 100% acrylic elastomeric resin and sticks to almost any surface.

Once dried, it forms a thick blanket of mold-resistant protection that expands and contracts like rubber and will tend to keep heat inside the grow area and even help absorb sound.

Note: you should use a primer like Kool Seal Kool Lastik Primer in order to make sure the coating sticks properly to your walls.

When using Kool Seal White Elastomeric Roof Coating, make sure you also get the primer or it won't stick well
Mylar (90-95% light reflectivity)

Mylar is an inexpensive reflective material that looks shiny and usually comes in sheets or rolls. "Foylon" is a more durable version of mylar and "C3 anti-detection film" is an infrared-proof version of mylar (which means it contains more heat). Mylar generally is offered in 1mm or 2mm thickness - the thicker the mylar, the more durable (resistant to tearing or creasing).

Mylar is a cheap and effective reflective option
Mylar can be difficult to clean and may need to be replaced after a few grows. It is not light-proof, but does help contain heat in the grow room, so it's important you create a good ventilation system to get rid of all the extra heat that's being contained in the grow area. If there are creases, tears, or the film gets dirty, the light reflectivity is dramatically reduced, so make sure it's placed flat on the walls and kept clean.
Mylar is effective until it gets dirty... unfortunately it's difficult to clean
"Just Okay" Reflectivity Options

Mirrors (good reflectivity for images but not for light...)

Mirrors seem intuitively like a great choice, but in reality they are "just okay" (at best) for reflecting the light of indoor grow lights back at your plants. While mirrors are great at clearly reflecting your image back at you, they just are not great at reflecting light that is actually usable to your cannabis plants. Mirrors don't reflect light from the grow lights in optimal patterns and tend to create light/heat spots. While better than a black wall, I recommend staying away from mirrors in the cannabis grow area.

Mirrors are not that great for reflecting light in the cannabis grow room
Styrofoam (60-70% reflectivity)

Styrofoam (Expanded Polystyrene Foam) is cheap, can be purchased in sheets, is durable and doesn't weigh much at all. Just hang on the walls, or styrofoam sheets can even be used as a "wall" all by itself. The uneven surface of styrofoam helps diffuse light without creating hot spots. When in a pinch, styrofoam is a great way to build your own reflective walls until you can replace with something better. Be careful though because styrofoam can easily melt!

Styrofoam is a cheap and light reflectivity option - just be careful because it can melt!
White Poster Board (up to 60% light reflectivity)

White poster board is inexpensive and readily available. Some growers will use it around the edges of the grow room, as well as for the floor and ceiling. While it is reflective when new, white poster board is difficult to clean and gets soft or moldy if it gets wet.

White poster board is an okay option for reflectivity, but only as a short term "quick fix"
Aluminum foil (55-60% light reflectivity)

Aluminum foil (also known as tin foil) is often used in the kitchen, and many growers will see that it's shiny and think it may be a good option to reflect light back at your cannabis plants. Despite what seems intuitive, the dull side of aluminum foil actually reflects light better than the shiny side. One of the problems with aluminum foil is it's easy to crease, and any uneven creasing can dramatically reduce the reflectivity. Some growers will crinkle all the aluminum foil, which can help diffuse the light more evenly. Aluminum foil will not burn your plants like some growers claim, but there are better reflective options out there.

Aluminum foil is actually an okay reflection option, but there are better options out there!
Emergency blankets (70% light reflectivity)

Emergency blankets are usually made of mylar, but usually come folded up instead of in a roll (making them easy to crease). These blankets tend to be very thin and easy to tear by accident. One of the advantages is these blankets are cheap so can be replaced often, but it is difficult to get them to lay flat against your walls.

Emergency blankets will do in a pinch, but they tend to crease more than other reflective options
Temperature in the Grow Room: Reflectivity

Certain reflectivity options tend to hold heat in, while others tend to let heat out. Which do you need for your grow setup?

If your grow room is cold...

Use one of the following recommended options to reflect back heat in the grow room...

Orca Grow Film
Kool Seal White Elastomeric Roof Coating
Mylar / Foylon / C3 Anti-Detection film / Emergency blankets
Styrofoam or aluminum foil (in a pinch - not great long-term options)
Or just get a grow tent, which will contain much of the heat unless you vent it out
If your grow room is hot...

Use one of the following recommended options to easily let heat escape the grow room...

Use flat white paint on the walls of your grow space to reflect back a lot of light, while absorbing some of the heat
However, a grow tent is the best option for hot grow areas because they come with built-in cooling options that make it easy to set up an exhaust and gain complete control over the temperature of your grow area
Learn more about controlling temperature in the grow room


Look for smooth surfaces in your reflector/hood. The more creases or "bends" in the reflector, the less effective it is.
Opt for a wide reflector above your plants. Narrow or small reflectors aren't able to bounce back as much light down at your plants. This is why "cool tube" reflectors have limited reflection abilities compared to other types of hoods.
Reflectors should be close to your lights and reflect light downwards at your plants

Learn more about different hoods and reflectors

Light Meters

While the above guides will help you get the most from your grow area, one of the best ways to actually test the amount of light your plants receive is to use a light meter (also known as a lux meter).

Light meters make it easy to directly measure the light levels in your grow room
A light meter actually measures how much light is being received at a particular spot. While light meters are pretty good for measuring the light from most grow lights, they are not as effective at measuring light from LEDs.
The Science: A light meter measures "lux," which is different from lumens. A lux is one lumen per square meter. Often you'll see light bulbs measured in how many "lumens" are given off. Lux is a better indicator of the amount of light received by your plants because lux measures how many lumens are received in a specified amount of area (measures luminous flux per unit area). This is what your plants care about. A bulb can gives off 20,000 lumens, but it's difficult to determine how much of that light is actually being received by your plants. Many factors will affect how many of those lumens actually "make it" to your plants such as how far the plants are from the lights and the reflectivity of your walls. While lux isn't perfect, it's better than using lumens.

Analogy: "Lumens" is like the horsepower of your car. "Lux" is like the speed.
It's important to understand that a light meter measures the total amount of viewable light, and doesn't measure the "spectrum" of light. A light meter can't tell whether the light is in the spectrum that your plants prefer or can use. This is why it's important to get grow lights made for plants like cannabis, so you don't have to worry about spectrum.

Not sure which grow lights to get? Read the cannabis grow light upgrade guide!

A light meter will measure the amount of "lux" and here's a good guide to help you determine if your plants are getting enough lux.

< 15,000 lux - sparse or "stretchy" growth - plant isn't getting enough light

15,000 - 25,000 lux - enough light for healthy vegetative growth

25,000 - 35,000 lux - plenty of light for fast vegetative growth, but not enough for optimal flowering

35,000 - 45,000 lux - optimal amount of light for cannabis plants in the flowering (budding) stage

45,000 - 75,000 lux - a lot of light and can be a waste of electricity compared to returns

> 75,000 lux - at this light intensity, you've hit the plant's "saturation point" which means your plant can't use all the light (be careful of light bleaching!)

Note: The only way to increase the plant's saturation point is to supplement with CO2.

Light meters will let you directly measure the change in brightness as you add reflective materials to your grow area, as well as adjust your lights so they are closer or further away from your plants.

Light meters are also useful for testing new or old grow lights to make sure the bulbs are as bright as they should be. As grow lights get older, they tend to produce less light over time, and a light meter can help you decide when it's time to change your bulbs or upgrade your grow lights.

Conclusion: Best Indoor Reflectivity Option

Hands-down your best option (if you can afford it) is to get a grow tent which is specially made for growing plants.

These tents have walls that are designed to reflect back the most light that is usable by your plants, and have reflective materials on all sides including the floor and ceiling.

Quality grow tents are light proof (no light gets in or out) and are designed to be hooked up to an exhaust system to easily control your heat. They are also water resistant and easy to clean. A grow tent is easier to set up and use than almost any other grow option. :vap-leafy_wave: PEAVE


Apr 10, 2014
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This is great info - thanks.
My grow tent is lined with white P.E. and I was getting some shade spots at the edges.
Until today when when I installed some cheap emergency blankets and now the light seems way more evenly distributed.
You are right about the issues of creases and issues with tearing and such. Hard to get them to sit flat against the walls too..especially with the negative pressure from the fan which bows in the sides of the tent. I wonder if its possible to iron out the wrinkles in the blankets?
Anyway thanks again-just the info I was looking for.

The Hemp Goddess

Delta, Panda film is so much more durable and so much easier to work with than any kind of mylar I have run across. However, flat white paint does almost as good a job as anything and it is cheap, durable, washable, and available virtually everywhere.


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Apr 18, 2014
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I use white shower curtains on my walls. Nice and reflective, easy to clean and..... cheap.

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