Shining a Light on Reflective Materials
Mimicking sunlight is the hardest and most important challenge for indoor gardeners at different stages throughout the growing process. Sara Elliott explores the illuminating world of light management to help you develop the best lighting strategy for your indoor garden.
Creating abundance is one definition of gardening, a slight of hand accomplishment that enlists the power of nature to help make plants grow faster and produce better yields.
Bringing a garden indoors sheds light on just how important illumination is to this process. Good lighting is critical, and what seems so natural and effortless outdoors can be difficult to duplicate within four walls.
Providing supplemental lighting is one of the first concerns of any indoor gardener, whether that involves opening the drapes to shine some light on a houseplant or setting up a large grow tent that will house multiple mature plants.
Making lighting choices comes from understanding how plants use specific wavelengths of the light spectrum during different stages of growth (PAR).
It also helps to know how to fully utilize the intensity of different light technologies while minimizing potential disadvantages like high energy consumption and heat buildup.
Managing Light in a Growroom
Multiple factors contribute to the development of an effective strategy for good light management beyond choosing a particular type of light technology.
One good example is the use of a reflector hood to divert light that would otherwise be wasted illuminating the ceiling. The hood reflects light back down onto the plants where it can increase light efficiency by 40%, or even more if the patterns of reflection overlap across multiple fixtures and reflectors.
Reflector hoods aren’t the only options when taking advantage of redirected light energy. Light reflected from a number of locations, not just from one or a series of overhead fixtures, helps approximate the diffuse lighting conditions in an outdoor garden. It’s an over, under, around and through approach to comprehensive, distributed illumination, and one that can mediate problems that arise when using focused light.
To get the best use of illumination, indoor gardeners place lights directly above plants and as close as possible without burning them. This maximizes the intensity of the light hitting plant leaves, and takes advantage of the inverse square law, which for our purposes states that light energy decreases the farther you move from the source of illumination. When plants are small, there’s no problem with this approach.
(Read also: How to Decide Between a Grow Tent and a Grow Room)
Seedlings are bathed in light, convert that light to food and grow big and strong, with the topmost growth getting the most intense energy. As those top leaves develop faster than the leaves beneath them, they create a canopy that blocks light from lower leaves and smaller plants.
The diffuse light that pervades an outdoor garden and provides energy to the undergrowth, resulting in balanced plant development, is either absent in an indoor growing environment, leading to spindly plants and other growing problems, or is provided through some other means.
This can be accomplished using side-mounted lights, but using reflective materials instead can reclaim light energy without the use of additional expensive fixtures, their increased energy costs and at least some of their freight of potential heat problems.
Using reflection to maximize light encourages many indoor gardeners to invest in dedicated growrooms and enclosures like grow tents that include light reflective walls, ceilings and floors.
Light Reflective Materials for Growrooms
Many materials reflect light and can be used to redirect light energy onto plants in a grow space or grow room. Some are more effective than others, and a few have been developed especially for horticultural applications.
For example, some embossed reflective surfaces designed for indoor gardens bounce light using faceted diamond, hammered or other dimensional textures for more diffuse coverage and less risk of creating hot spots—inadvertently focused light energy that can burn plants.
This is distinct from specular or flat reflective surfaces that need to be smooth and clean to remain effective. By some estimates, reflective materials working in concert with an efficient set-up where plants are carefully spaced can increase light efficiency by up to 30%.
There are lots of reflective materials on the market, from the metals in reflector hoods, to films, non-woven fibrous sheets and paints. Let’s take a look at a few different options to see how they shine:
Aluminum Foil – A popular do-it-yourself choice, aluminum foil isn’t a particularly effective reflector, even though it can produce an impressive amount of glare. Generally considered 50-55% reflective, that number drops drastically when the surface deforms, which can happen easily, producing hot spots.
Mirrors – If you’ve thought of using aluminum foil to reflect light onto your plants, the notion of employing a mirror probably wasn’t far behind. Depending on the backing materials involved (aluminum silver, gold), mirrors absorb some light wavelengths, while having the potential of disrupting the wavelengths plants need most.
They create dangerous hot spots, too. Almost as bad, mirrors are notoriously susceptible to delamination in moist conditions, so, after you realized the mirror is hurting your plants, you’ll discover you’ve ruined your mirror, too. There’s a good reason you don’t see mirrors in grow boxes or tents.
White or Light Paint – You may have noticed plants situated next to a white or light-colored outdoor garden wall grow faster than other like plants in the landscape. This is due to the power of reflected light energy in action.
A simple, light-colored paint can help increase the available light to indoor plants, too. Paint is inexpensive, readily available and easy to use. When kept clean, it is also one of the most reliable light reflective surfaces around. Flat, bright white paint from any local home improvement store will be 75% reflective or more.
Some reports place that figure at closer to 90%. It may seem counter intuitive, but glossy paint will not reflect as well as flat paint, so keep that part simple. It’s also worth noting that a smooth wall will reflect light more evenly than one with imperfections.
Oh, and save yourself the hassle of prepping bare surfaces by purchasing a paint and primer in one product. While perusing paint labels, you might also consider a paint that contains a mold control additive that can help limit the development of mildews, molds and fungi in wet or humid locations like floors, tabletops and benches.
Mylar – Mylar is the brand name of a variety of chemically stable polyester film that can be highly reflective. Think shiny Mylar balloons and you have the general idea. This material is also referred to as BoPET, short for its technical description: biaxially oriented polyethylene terephthalate.
Mylar can be up to 97% reflective, and is available in thicknesses of 1 mm and 2 mm, and in smooth and textured finishes. It is popular for use in grow tents, where this extruded and stretched product is bonded to the interior walls, ceiling and floor, while a thick canvas fabric is used for the outer shell. Mylar is also sold in rolls. It has the advantages of being effective and flexible.
Mylar reflects heat and may retain moisture long enough for it to become a problem. The 1-mm sheets can be fragile, and it may lose effectiveness over time through the action of moisture, dust and dirt accumulation and the transfer of body oils through physical contact.
Smooth Mylar sheets are known for producing hot spots, especially when scratched, creased or otherwise deformed. Most experts recommend paying a little more for patterned Mylar because it reduces instances of hot spots and broadcasts light the best.
Foylon – Possessing many of the same characteristics of Mylar, Foylon is a laminate made of spun polyester fabric and aluminum. It is widely considered more rugged and durable than Mylar and has a reflectivity of 95%.
Foylon is tear resistant, which makes it relatively easy to position, clean, reposition and maintain. Like Mylar, Foylon also reflects heat, and using it may require increasing the ventilation in an enclosed space.
Black and White Polymer – This synthetic poly film is white on the front and black on the back. In part, this is to help block exterior light and maintain photoperiod integrity. Poly has a 90% reflectivity rating. It is also waterproof and algae, mold and mildew resistant. Poly is often recommended for DIY projects because it’s durable and easy to work with. For heavy-duty applications, consider the thicker 6-mm rolls.
Reflective Microfiber – This fabric product has up to 94% reflectivity and excellent diffusion thanks to the scatter pattern produced by the millions of compressed fibers on its surface. It isn’t as critical to maintain a smooth wall or other surface when using reflective microfiber fabric because this product’s enhanced diffusion features make hot spots less of an issue.
Reflective microfiber is also tear resistant, mold resistant and easy to clean. Although it has a black, light-blocking exterior surface like poly film, it is a very different product, with better diffusion and reflectivity.
Additional Growroom Reflective Material Tips
There are a couple of other things to consider when adding a reflective material to your grow space. Reflected light is most effective in close proximity to plants. This is one time when “roomy” isn’t an advantage. If the airflow is good, the closer the plants are to the reflective material, the more they’ll benefit. Remember the inverse square law.
Installation planning is another important consideration. Reflective films like Mylar should hang smooth and wrinkle free. Ripples and wrinkles are what cause hot spots, and even minor imperfections like scratches and small tears can have negative consequences. If you’re looking for an easier way to install these types of materials, try using adhesive hook-and-loop tape.
Once the tape is mounted, adding the panels in a way that will produce a smooth finish is easier, and incurs less risk of accidentally tearing the film than using staples, glue, tacks or nails. If you’re careful, this option also has the advantage of allowing you to more easily re-position panels or remove and install them in another location later.
(Read next: The Importance of Air Purification in the Growroom)