Supplemental Lighting for Lower Flowers: How to Choose LED Lighting for Under-Canopy and Inter-Canopy Use

Lower-quality flowers from the lower parts of plants, nicknamed “popcorn”, can in some cases account for as much as a third of the harvest. This is because they grow sheltered in the shade of the leaves above them. Equip your grow with supplementary lighting and get the most from the lower parts!

A simple rule applies to indoor growing – where light cannot reach, little will grow. Unlike outdoor growing, where the Sun travels across the sky and illuminates plants from all sides, indoors light falls directly from above only. Flowers in the lower parts or inside the plant canopy are exposed to less light than the tops and tend to be looser and poorer in terpenes and other secondary metabolites. Shaded areas in the crop are also often a hiding place for pests and a breeding ground for mould.

Is lighting the lower parts worthwhile?

Lighting the lower parts is certainly not bro-science, and many commercial growers use supplementary lighting to increase both yields and crop quality. Studies estimate that under-canopy and inter-canopy lighting can achieve approximately 20–30% higher yields. Another advantage is that illuminated flowers will have a terpene profile and structure comparable to those of the tops.

In terms of electricity consumption, operating supplementary lighting is not particularly expensive. Compared with the main light, which usually has a power consumption of several hundred watts, most supplementary lights consume up to 100 W, while the most powerful under-canopy lights have a power consumption of 120 W.

How to use supplementary lighting

Do not switch on the additional lights too early, as this would be energy wasted unnecessarily. The best time is approximately 14–21 days after switching to the flowering phase. Be prepared for the fact that more lights create more heat, and adjust the settings of the ventilation, dehumidifiers, heating and other equipment. For example, it may be necessary to add circulation fans to the bottom of the grow box in order to maintain a suitable microclimate.  

If possible, match the spectrum of the supplementary lighting to the main lights. If you use full-spectrum lights, the supplementary lighting should also have a full spectrum. If you decide to enrich the main light with, for example, a far-red part of the spectrum, the supplementary lighting should also contain this part of the spectrum.

Position LEDs for lighting the lower parts approximately 20–30 cm below the leaf canopy. Some additional panels can also be used for lighting the plants from the side. Simply attach them to the corner poles. If you decide to place an additional light inside the canopy, choose a light with a power consumption of approximately 20–30 W, which will not scorch the leaves and tops of the plants.

You may also be interested in: How to improve canopy light penetration through defoliation

LEDs for lighting the lower part of the crop and inter-canopy LEDs

Faven Chroma LED 120 W Under Canopy Light 3.0 - Multispectral grow light designed specifically for illuminating the lower part of plants. In addition to a full spectrum, the module is equipped with 15 W far-red LEDs, including an independent channel, so the spectrum can be adjusted according to requirements.

Gorilla UnderCanopy LED 120 W - Full-spectrum light for illuminating plants from below, with dimming so that you can adjust the lighting intensity to suit the plants. This module can be connected in series (max. 20 lights).

SunPro Intercanopy LED BAR 25 W, 3.3 umol/J - Double-sided light with a balanced spectrum designed for side lighting. The module produces minimal heat, so it can be placed very close to the plants, including inside the canopy.

Lumatek LED Full-Spectrum 100 W BAR 2.9 - Full-spectrum supplementary LED panel with high output, which can be used for lighting the lower parts of plants or as a side light source. 

TLED Secret Jardin 42 W - flowering and TLED SunPro Bloom 42 W - flowering - Supplementary TLED panels with a spectrum that supports flowering can be used to illuminate the lower parts or as a side light source.

TLED SunPro Bloom 26 W - Supplementary TLED panels with a spectrum that supports flowering and a lower output are suitable as supplementary lighting for smaller grow boxes or as inter-canopy lights.

You may also be interested in: Important metrics for choosing grow lighting

Remember that, in addition to supplementary lighting, you can improve light penetration into the canopy through pruning, training plants into a net, defoliation and other LST techniques. You can learn how to do this and much more on the HiGarden blog.