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By: HTG Supply on 02/16/2018

What is Supplemental Lighting?

The practice of supplemental lighting is the use multiple types of grow lights designed to accomplish different growing objectives. The primary indoor garden lighting strategy involves the use of overhead grow lights to provide light for the growing area. Supplemental lighting can simply be adding more light but it is also using light that affects plants beyond photosynthesis. Light colors are actually light frequencies; different light frequencies (colors) will affect plant physiology. So, specific colors/types of light can be used during specific growth phases to improve growth.

When thinking about supplemental light, you can focus on two main parameters: 1) high output/intensity, and 2) a broad range of light frequencies suited for the plant growth you want. Grow lights that provide intensity and a broad frequency fall under the category of “primary lighting”, which can include any of the various grow light types.

There is no artificial light source that can replicate the overall quality of light produced by the sun. Each light has its advantages and its drawbacks in terms of light spectrums, intensity and/or coverage. Moreover, every species of plant has specific lighting need from one growth phase to the next. This is where advanced growers start to adjust supplemental lighting to get the most from their indoor garden space.

Supplemental Grow Light Spectrums

The two most important types of light for plants are red and blue light, which is why many LED grow lights feature these frequencies. All plants need these two colors to conduct photosynthesis. Beyond photosynthesis, the amount of these two colors, as well as other frequencies of light, can dramatically promote different physiological responses. For example, if plants receive a higher percentage of blue light they will have short growth between nodes and more leaf growth. When plants are given a higher percentage of red light they will have greater distance between nodes and will be encouraged to flower. Infrared light is a frequency that can’t be seen by human eyes, but it can dramatically speed up and increase the flowering response for some plants. Ultraviolet light is another frequency of light humans can’t see but one that can also alter plant growth indoors.

One of the first examples of supplemental lighting spectrums most growers learn is the combined use of metal halide (MH) and high pressure sodium lights (HPS). Metal halide lights with their bluish-white output promote compact vegetative growth, while the yellowish-red output from HPS grow lights promotes flowering production. Using the two lights together was better than using two of the same type of lights. Exposing plants to a higher percentage of MH during vegetative and a higher percentage of HPS during the flowering phase greatly increases plant growth and yield.

Ultraviolet & Far Red

Supplemental light doesn’t just target red and blue wavelengths to in order boost photosynthetic rates. Examples including ultraviolet (UV) as well as infrared (IR) and far-red waves. These wavelengths don’t factor significantly into photosynthetic rates, but they do affect plants, and in some very interesting ways. It’s important to note that UV and IR lights should generally be operated independently from primary lights, and run for short intervals in your garden, read on to see how and when.

Supplemental UV Lights

Wavelengths between 100-400nm are referred to as Ultraviolet or UV light. Although UV grow lights don’t contribute much in the way of photosynthetic activity, they have several beneficial uses in the indoor garden. Plants that are started indoors to be transplanted outside must be acclimated slowly to natural sunlight due mainly to the presence of UV. Traditionally, a process called hardening-off has been used to make the transition without shocking of killing young plants. This involves moving plants back and forth from indoors to outside, each time leaving them outdoors longer, over a period of several days. Needless to say, this is not on many growers’ list of favorite garden activities. Supplemental UV lights, including several varieties of T5 Bulbs, now make it possible to greatly reduce or eliminate the hardening-off process – read more about hardening off.

In addition to improving indoor to outdoor transitions, UV grow lights can also produce changes/increases in phenolic compounds, flavonoid pigments, resins and oil production, etc. As plants are exposed to UV light, they produce such compounds to protect themselves, similar to the way you might put sunscreen on so you don’t get sunburn. While these effects are highly desirable for many crops, most primary lights offer little if any UV component. Several UV lights have been developed recently for this purpose, the strongest among them being the AgroMax Pure UV bulb. A single 4’ Pure UV T5 bulb at 54 watts is able to effectively supplement and produce results for up to a 4’ x 4’ area.

Far Red Light for Plants

One of the more recent and interesting developments in horticultural lighting is the emergence of supplemental far red lights, primarily in the form of LED grow light bulbs and light bars. The far red frequency will encourage young plants to develop larger leaves and will also affect photoperiodism (Flowering phase) of short day plants. When short day plants are exposed to far red light, it will encourage them to flower. So, many growers will use far red lights like a 730nm LED light bar for a few minutes up to two hours before the lights off phase. Doing this will speed up flowering, meaning you will see flowers develop quicker than without far red light.

Supplemental Light Intensity

As we mentioned above, supplemental light doesn’t just deal with improving spectrum. It can also improve the uniformity of light intensity for a boost in production throughout the garden. No matter how great your primary grow light(s) is, all grow lights are subject to a principle known as the Inverse Square Law. Put simply, the farther light travels, the weaker it gets, and it doesn’t weaken steadily! Instead, it weakens exponentially, meaning if your light is at 100% brightness from a distance of one foot, moving it to a distance of two feet (doubling the distance) makes the light 25% as bright, not 50%. What this means for you and your garden is pretty straightforward – the leaves on the bottom of your plant aren’t getting nearly the amount of light as the ones at the very top. This is also the case for plants on the sides of the garden vs. those under your lights.

Space is important to think about indoors. The size of your grow area should match the light (AKA, light coverage). Side lighting is one of the most common techniques to improve light intensity and coverage. As the name suggests, this method involves lighting plants from the sides as opposed to just from above. By placing lights around the perimeter of your garden, it’s possible to have higher light intensity everywhere so that you will have healthy leaves and growth over the entire plant. Low-wattage, low-heat options like LED grow light strip and T5 single bulb fixture types are perfect for side lighting and you can also use these lights to providing beneficial spectrums by using blue and or red lights

How to Use Supplemental Grow Lights

So, now that we’ve gone over what supplemental lighting is, let’s talk about how to do it. We’ll take a look at what each type of primary grow offers and compare that to the types of supplemental lights that are available, so you can be sure that you’re covering all the bases. The light types are listed in order of intensity, so the lower lights on the list will benefit even more from side lighting versus the lights at the top. The type of supplemental lights are listed for vegetative growth vs. flowering growth benefits.

High-Pressure Sodium (HPS)

HPS lights, give off a starkly reddish-orange or yellow color. These lights are very bright and are excellent for plants in the flowering stage of growth. The downside is they tend to lack frequencies of light that promote vegetative growth, and most provide little to no UV light. They also produce a lot of heat and must be positioned several feet above the canopy unless you purchase a light that can be integrated with grow room ventilation. The light intensity is high enough you can just keep the light 3-4 feet above the lights with a fan but this creates an uneven light distribution. What this means is that some parts of your garden will receive less light than others. Side lighting with blue frequency lights is one of the best supplements to go with an HPS – read more about supplementing HPS grow lights-read more about supplementing HPS grow lights.
Vegetative supplements:

• Overhead/side-lighting full spectrum LED’s or T5’s to promote even growth throughout the garden
• Overhead CMH for improved spectrum and coverage
• Blue-centric supplemental LEDs or T5’s to boost overall vegetative growth and prevent stretching
Flowering supplement:
• UV T5 grow lights to increase essential oil/resin production
• Far red LED strip lights or bulbs to boost growth and reduce turnaround

Metal Halide (MH)

Metal halide lights typically cast a whitish-blue “daylight white”. The spectrum emitted by MH lights is predominantly blue, making it better for vegetative growth than for flowering. While they encourage lateral growth and prevent stretched or spindly plants, MH lights are slightly lower on the intensity scale compared to their HPS counterparts. For example, a 400 watt metal halide will have a lower luminous output than a 400 watt HPS lamp.
Vegetative supplements:

• Overhead/side-lighting full spectrum LED’s or T5’s to promote even growth throughout the garden
• Overhead CMH for improved spectrum and coverage
Flowering supplements:
• Switch to or add HPS to overhead lighting for a boost in overall growth and flowering production
• Red-centric supplemental LEDs or T5’s to boost flowering
• UV T5 grow lights to increase essential oil/resin production
• Far red LED strip lights or bulbs to boost growth and reduce turnaround

Ceramic Metal Halide (CMH)

CMH lights are truly “next level” grow light technology. As they correct the imbalances of typical HID grow lights, they themselves can be used for supplemental purposes. Ceramic metal halide grow lights offer a fuller spectrum as well as improved efficiency vs. other HID types. Because of the full spectrum and the lower power consumption of these lights, CMH lamps are great supplements to just about any other kind of light! That said, they offer a bit of a smaller footprint than other HID so supplementing them is also a benefit.
Vegetative supplements:

• Overhead/side-lighting full spectrum LED’s or T5’s to promote even growth throughout the garden
• Lower wattage overhead CMH to improve coverage & growth
• Blue-centric supplemental LEDs or T5’s to boost overall vegetative growth
Flowering supplements:
• Red-centric supplemental LEDs or T5’s to boost flowering
• UV T5 grow lights to increase essential oil/resin production
• Far red LED strip lights or bulbs to boost growth and hasten flower development

Light-Emitting Diode (LED)

LED’s are very popular right now, and the reasons are numerous. First off they are the most energy-efficient light source by far. Second, LED’s emit very little heat, and have a far longer lifespan than other lamp types. And, most important to supplemental lighting, many varieties can be adjusted to provide refined spectrums or specific combinations of light spectrums and intensities. The downside is most LED’s don’t provide the same light penetration as HPS, MH, and CMH. Newer and more advanced fixtures such as COB LED grow light models are beginning to overcome this issue, but the technology still comes at a relatively higher cost.
Vegetative supplements:

• Side-lighting full spectrum LED’s or T5’s to improve light penetration for taller plants
• Overhead full spectrum LED’s or T5’s for improved coverage uniformity
• Blue-centric supplemental LEDs or T5’s to boost overall vegetative growth
Flowering supplements:
• Red-centric supplemental LEDs or T5’s to boost flowering
• UV T5 grow lights to increase essential oil/resin production.
• Far red LED strip lights or bulbs (separate fixture) to boost growth and reduce turnaround

T5 Fluorescent

T5 lights come in a wide variety of spectrums and are some of the most customizable in terms of different combinations and applications. Perhaps one of their strengths is the coolness and wide spectrum bulb options make them ideal for seedlings and small plants. While multi-lamp fixtures offer a nearly endless combination of primary and supplemental bulb combinations, fluorescent T5 grow lights are not the most powerful or energy-efficient lights when you’re growing larger plants. However, they do offer a fantastic range of spectral options and can be cheaply configured to provide better coverage for any size of the garden.
Vegetative supplements:

• Side-lighting full spectrum LED’s or T5’s to improve light penetration for taller plants
• Blue-centric supplemental LEDs or T5’s to boost overall vegetative growth
Flowering supplements:
• Red-centric supplemental LEDs or T5’s to boost flowering
• Pure UV T5 grow lights – in a separate fixture – to increase essential oil/resin production.
• Far red LED strip lights or bulbs to boost growth and reduce turnaround

To sum it up, plants use a wide range of light, even frequencies not visible to the human eye, and no one grow light provides optimal levels of every frequency. Similar to the way we use nutritional supplements to improve our diet and boost our energy, you can supplement your plants’ ‘light diet’ with ranges of the spectrum lacking in your primary grow light(s) to improve your harvests. There are combinations of lights designed for every application, stage of growth, layout, and garden size. Ultimately, the type of supplemental lights that will work best for you will depend on your specific plants, what type of primary lighting you’re using, and the effect you’re looking to achieve.

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Questions, tips, or tricks to share? Join the conversation, and share your experiences with supplemental lighting! Throw a picture on Instagram and tag us in it (@HTGSupply) – we’d love to see your results! And don’t forget to check out this week’s coupon code and sale information below! From all of us here, good luck, stay safe, and Happy Growing!

TALKING SHOP COUPON CODE: SUPPLEMENTALEnter the promo code at checkout for a 10% discount on select the supplemental lighting fixtures and bulbs products featured below. Visit your local HTG Supply and simply mention this article to get the deal in-store as well! Thanks again for tuning into Talking Shop with HTG Supply! Offer valid through HTGSupply.com and in-store 02/16/18-03/02/18. Cannot be combined with other offers. Follow us on social media for all the Sales, Events and Customer Appreciation Days. In addition, learn more about indoor growing and get all kinds of tips, tricks and techniques!