Back in the Day…
I first saw side lighting in action during a visit to a Canadian indoor farm with a low ceiling. Normally, this would necessitate lower wattage fixtures and smaller plants—but these plants were huge (by indoor standards), almost touching the ceiling!
The grower didn’t use top lights—instead, he illuminated his plants from the side using bare 1000W High Pressure Sodium (HPS) lamps positioned in between the rows, hung vertically and directly from their electrical cables on light movers! No reflectors (or health and safety inspectors) in sight. Also, HPS lamps emit light through 360 degrees, perpendicular to their arc tubes, so there was significant light loss to walkways. However, the grower was convinced that the lateral blast of intense light upon the flanks of his plants was key to his garden’s productivity and crop homogeneity.
Today, LED lighting technology is potentially unlocking side lighting as a supplement to top lighting, rather than a replacement. Modern indoor growers enjoy many more options than my old Canadian friend had when it comes to lighting their indoor plants efficiently.
The Case for Side Lighting
Full-spectrum LED top lighting is now the go-to photon generating solution for indoor growers. The most popular style of LED top light is the multi-array LED; these fixtures are known for their efficacy (up to 3.0 µmol/J — over twice that of old school single-ended HPS lamps from back in the day) but the penetration power of multiarray LEDs is comparatively lacking. The radiant intensity generated from those old school HPS lamps, notwithstanding their lower photon efficacy, was incredible, with every photon emanating from a small, cylindrical arc tube. Multi-array LED fixtures, on the other hand, are well-known for lighting canopies evenly and effectively at high PPFDs, but this light source is spread over hundreds, sometimes thousands, of tiny little diodes. The resulting light is powerful, but different in quality, with lower radiant intensity.
Accordingly, if you measure incident light intensity at the canopy under a multi-array LED fixture, your PAR meter will read impressively high numbers— 900 µmol/m-2/s-1 and higher—but move the sensor just a few inches below those top level leaves and it’s night and day. In this scenario, the lower leaves are a net drain on the plant, requiring more energy to maintain than they generate via photosynthesis. No wonder then that indoor growers often strip away these lower leaves in an effort for plants to focus all their energies at the canopy where all the action is.
Leaf stripping can be incredibly laborious and time consuming, even for small indoor gardens, however. What’s more, grower often end up with bin bags full of stripped-off foliage—foliage that’s taken time, energy, water and nutrients to produce—which effectively ends up on the compost pile. Efficient? I think not.
Sure—outdoor growers of light-loving plants species often prune and thin-out foliage to improve light penetration, but it’s not as necessary a practice outdoors as it is indoors thanks to the high radiant intensity of the Sun and its diurnal path across the sky each day. The movement of the Sun from east to west helps to expose all parts of the plant, including the sides / flanks, to direct sunlight. Similarly, side lighting in the form of LED bars could potentially offer a novel solution to the problem of ‘top-heavy’ lighting, helping to illuminate your plants in a more three-dimension and balanced fashion, where the middle and lower regions of your plants also receive sufficient light to drive full generative development, not just the tops.
Practical Considerations When Choosing Side Lighting LED Fixtures
- Spectrum: While red dominant spectra are recommended for subcanopy lighting, side lighting is best applied as full spectrum—the same as your top lights.
- Power: Minimum 150W of total LED side lighting power per 1.2 metres of ‘side’. I recommend 2 x 100W Maxibright DAYLIGHT LED bars arranged in an ‘equals sign’ formation, about a foot apart.
- Distance from Plants: The closer, the better… to a point. 30 – 40 cm for 100W LED bars, and up to 60cm for 300W bars. Plants may require lateral training as lateral growth tips tend to grow towards the side lights.
- Heat Considerations: Adding side lights can increase air and leaf temperatures. With LED-illuminated rooms this is often a bonus and can reduce reliance on heaters during the cooler months.
- Timing: Add side lighting at the earliest possible stage so plants become accustomed to it. Many plants will respond negatively (scorched leaves and fruits) if powerful side lighting is introduced, say, half way through flowering. By this time, leaves (and fruits) have adapted to light, semi-shade, or shade conditions and a sudden increase in light intensity can easily lead to scorching. Use a dimmer to gradually increase the intensity of your side lights to mitigate the risk of shock.
- Robustness: Ensure your side lighting lighting fixtures are rated IP65 or higher as they may well be more prone to getting knocked.
- Fixing: Mount your side lights a few inches from the wall so there is adequate air gap behind them for sufficient thermal management. Side lighting (with sufficient power) is typically not suitable for use inside grow tents as the tent fabric will be too close to the back of the light bar.
- Increased Transpiration and Feeding: More light = more transpiration. Growers using side lighting may need to increase irrigation frequency, commensurate with the increase in total light output.
My Side Lighting Experiments
Over the last 18 months, I’ve tested many different side lighting configurations. I’ve repurposed 300W single bar ‘top lights’ with 140 degree optics; I’ve turned folding (remotely ballasted) multiarray LED fixtures on their sides; I’ve also experimented extensively with single LED bars of different wattages and spectra.
What did I discover? In a nutshell—not all “side lights” are equal! Assuming you’re growing light loving plant species and attempting to cover 120 cm of ‘side’ indoors with your ‘side lights’ (that’s around four feet), as a general rule of thumb, anything under 100W of extra side lighting power—even at the high photon efficacy rates of modern LED lighting—is a waste of time and energy. Suffice to say, those 22 watt LED T5 replacement tubes should stay in your propagation tent. Similarly, I’ve seen a few ‘clip on’ side light bars designed to work inside grow tents—typically around 44 watts. Another waste of your time and money. While many of these light bars will certainly look pretty and illuminate the sides of your plants to your naked eye, most simply lack the necessary intensity to make any difference at all.
Conclusion
My peach habanero chillies responded well to side lighting with abundant fruit production and impressive lateral growth. Direct light on habanero fruits can be beneficial and contribute to their development, but it is the overall light exposure to the plant, particularly its leaves, that is crucial to drive maturation. Other light-loving plant species, particularly those with photosensitive florets, arguably stand to benefit even more from side lighting.
Here Are Some Key Benefits of Using Side Lighting in Indoor Grow Rooms
- Improved Light Penetration and Distribution
Dense canopies can prevent light from reaching lower leaves, leading to wasted energy and a massive VPD differential between the top and bottom of the plant. This can lead to plant stress , stunted growth and uneven plant development.
- Increased Yields
Additional light exposure, particularly from side lights, can increase the number of flower sites and improve yield and crop homogeneity, helping the whole plant to ripen at the same time. Plant species with compact, dense florets benefit most significantly from side lighting.
- Bushier Growth
Side lighting encourages plants to grow fuller and bushier, avoiding elongated stems—but be careful that your plants don’t venture too close to your side lights.
- More Vertical Wiggle Room
If your plants are growing closer to your LED top lights, it’s possible to dim them down a little and divert the energy you save to your side lights for better light distribution and energy utilization.
- Optimal Plant Count
Some growers are attracted to the notion of fewer but larger plants. Irrigation set-ups can be simplified and growing can be a less stressful with fewer mouths to feed.
- Reduced Stress for Plants?
Side lighting can potentially create a more balanced environment, reducing phototoxic stress and promoting healthier growth with less variation in vapor pressure deficit (VPD) across the plant. However, if growers do not adjust irrigation frequency and volume to match the increase in light output, the opposite can be the case. Take it easy with nutrient solution strength as you adjust to newly installed side lighting.
- Enhanced Flavor and Potency
Side lighting, especially full spectrum LED light bars, can increase trichome production in herbs and medicinal plants, leading to enhanced flavors, aromas, and potency.
- Dual Advantage in Cooler Months
Side lighting can provide additional warmth to the garden, making it a smarter choice than traditional heating methods during colder months.
- Time-Saving in Maintenance
Implementing side lighting reduces the need for time-consuming leaf stripping or lollipopping, making garden maintenance more efficient. You may still need to remove some leaves though, especially if they are blocking flower sites.
- Higher Crop Homogeneity
Indoor growers using top lighting only often report a marked difference in ripeness and overall quality in the flowers and fruits taken from different parts of the plant, with the highest quality always coming from the canopy. This won’t change with side lighting, but the crop quality will be much closer and homogenous throughout.
Indoor horticultural practices have evolved significantly in the last few decades. Side lighting using LED light bars offers a multitude of benefits, from enhanced light penetration and distribution to increased yields and crop uniformity. By meticulously selecting the right fixtures, considering the specific needs of the crop, and adhering to safety and efficiency standards, growers can unlock the full potential of their indoor gardens. Embracing side lighting, with an informed and strategic approach, represents a forward step in the pursuit of horticultural excellence and sustainability.
TLDR:
- LED technology has essentially unlocked the viability of side lighting.
- Side lighting with LEDs offers indoor gardeners a way to enhance light distribution, ensuring that not just the tops but also the sides and lower parts of plants receive adequate light.
- Plants benefit from side lighting outdoors, thanks to the diurnal movement of the Sun.
- Side lighting can increase yields, improve crop homogeneity, and allow growers to benefit from more efficient use of space and energy.
- Not all side lighting solutions are created equal; many “side lighting solutions” sold online are merely notional and underpowered.
- Proper installation is critical to achieving desirable outcomes. Side lights need to be close to plants. Safety, spectrum, power and heat management are the practical considerations when implementing side lighting
Footnotes: The Science of Side Lighting
Side lighting has been found to significantly enhance plant growth, improve the internal structure and arrangement of chloroplasts in leaves, induce smaller stomata with higher density, promote stomatal opening, and improve photosynthetic efficiency, leading to enhanced branching and flowering in plants such as chrysanthemum. This indicates that side lighting can positively affect the morphophysiological characteristics of indoor plants, especially in terms of their growth and development (Yang & Jeong, 2021).https://www.mdpi.com/1422-0067/22/21/12019
Lighting from both the top and side can enhance photosynthesis and plant performance by improving light usage efficiency. This results in better branch formation and earlier flowering, suggesting that the optimal combination of various lighting directions can positively influence plant morphophysiology (Yang, Song, & Jeong, 2022).https://www.mdpi.com/1422-0067/23/5/2448
Polychromatic supplemental lighting from underneath the canopy can enhance tomato plant development by improving leaf photosynthesis and stomatal regulation, demonstrating that proper light orientation and spectrum can significantly impact plant growth and development.
(Song, Jiang, & Gao, 2016). https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01832/full
by Everest Fernadez from the Just for Growers YouTube channel.
