Lighting Design Matters: Three Things to Consider

In recent years, there has been significant progress in the development of innovative light fixture options available to indoor gardeners. When choosing an appropriate fixture for your indoor garden, there are a few aspects you need to consider to obtain desirable results, such as light spectrum, photometric output and cooling options.

If these aspects take priority in your lighting design decisions, you can achieve significant improvements in the areas of yield and electrical usage efficiency. Here is a brief overview of some lighting design options available to modern gardeners.

Light Spectrum

The light spectrum that your lighting system produces drastically affects the quality and quantity of the plants you’re growing. For example, when you’re flowering a photoperiod cultivar that requires large amounts of photosynthetically active radiation (PAR), the light spectrum produced by a high pressure sodium (HPS) lamp or a ceramic metal-halide (CMH) lamp will consistently produce high-yielding results. Both of these types of lamps incorporate a significant amount of red and green colors in their light output, efficiently driving photosynthesis in flowering plants.

When using HPS bulbs, I recommend selecting the newer, double-ended (DE) bulb designs, as they provide a significant advantage in efficiency over the older, mogul-based designs, producing about 1.28 times more usable light than mogul-based HPS lamps with the same power input. On the other hand, CMH lamps are being adopted by many gardeners due to their low heat output and high-yielding results, but there seems to be prevailing reliability issues with the ballasts used to drive them, and replacing the ballasts is expensive.

Looking to the future, with regards to spectral output capabilities and efficiency, light-emitting diodes (LEDs) may be the next-level solution. That being said, further testing is needed to determine the most economical fixture design and best-practice techniques for successfully incorporating these lamps within an indoor agriculture facility. I believe horticultural LED fixtures are still in the early stages of development, but with more research, these lights could become a cost-effective solution for reliably growing top-quality, high-yielding indoor plants.

Photometric Output

The photometric design of a lamp fixture determines how the light is delivered to the plant canopy by shaping the distribution of brightness over a defined target area. By changing the shape and the angles of the reflective or refractive surfaces within the fixture, light can be directed to specific locations on the plant canopy.

Most indoor growers prefer a uniform light distribution over the desired canopy area, and fixtures that have significant hot spots (bright spots) are typically avoided, as the canopy quickly becomes uneven, which either makes more work for the gardener, or creates yield inefficiencies due to shading or light burn.

Assuming the fixture can provide uniform light distribution, light-on-target efficiency should be the next most important factor in selecting the appropriate grow lights. A reflector that minimizes the amount of light wasted on walls or the floor by directing the light to a defined target area provides the best results.

Cooling Options

For a garden to operate successfully, temperature control is an absolute necessity. The amount of light needed to produce high-yielding plants generates a lot of heat that must either be removed from the space or cooled.

Some fixtures are equipped with built-in duct connections, allowing for strings of lights to be connected in a series. Fans are then used to remove as much of the heat produced as possible. However, depending on how well-insulated the ductwork and light fixtures are, this will typically only account for 20-30% of the total heat generated by the lamps. The remainder of the heat needs to be cooled by air-conditioning equipment.

For any reasonably lit indoor garden, standard air-conditioning systems intended for human comfort are insufficient. However, multiple options exist for extending your cooling capability, including residential-style split units used to supplement household AC, but the most energy-efficient heat removal methods use industrial-process cooling techniques, incorporating liquid-based cooling technologies to provide the most efficient environmental control.

Fixtures that incorporate on-board, liquid-based cooling features have been on the market for quite some time now in an attempt to increase the efficiency of indoor garden cooling mechanisms. Some designs pass liquid in a sheath over the bulb to remove the heat, but this has the negative side effect of altering the spectral output of the bulb and lowering the amount of light delivered to the plant canopy.

Newer fixtures use liquid-based heat exchangers and fans to cool the heat generated without passing water or cold air directly over the bulb, leaving the spectrum and light output intact while still removing the excess heat before it enters the growth chamber. With these modifications, built-in, liquid-based cooling features are now a viable option for indoor gardening.

How to Choose the Right Grow Lights

Choosing a lighting design may seem difficult with all of the options available on the market today. The most practical approach is to pick the most efficient, reliable and proven technology available in your price range.

Over the last 20 years, indoor gardeners have proven that the HPS spectrum is a great light source for plants, and with the development of the more efficient double-ended bulb, it is currently among the most reliable and cost-effective light sources for gardens of any size. There are now several fixtures available that incorporate the double-ended HPS bulb, so let photometric output—how much light is reaching the plants—be the next guiding factor.

Look for a fixture that provides the most light-on-target while minimizing hot spots. Some fixtures are designed for use in greenhouses, while others are designed for use indoors. Fixtures designed for greenhouse applications have a small reflector that casts a wide light spread, displaying less efficient light delivery to the canopy under indoor-only growth conditions while providing fewer options for cooling methods.

Newer fixtures created for indoor-specific applications are designed to efficiently deliver light to the canopy, minimizing light waste while also incorporating various methods for effectively cooling the heat produced by the bulb.

Finally, look for fixtures that provide liquid-cooling technologies. Liquid-cooling technology is frequently used in high-heat environments, and I believe the additional efficiency and control options you’ll experience using liquid-cooling are unmatched.

No matter how big or how small, indoor gardens are driven by efficiency. Whether you’re a hobby grower interested in alleviating costs, or you’re running a large production facility and are looking to improve your bottom line, your lighting design is the key to success. Choose wisely and you will soon be producing larger crops while spending less money on electricity and labor.