Indoor Grow Lights: T5 Grow Lights - Happy Hydro

LED and HID grow lights may make up the lion's share of the cannabis grow light space. However, there are still dedicated indoor cultivators that rely exclusively on (or in part) fluorescent grow lights for growing indoor cannabis. 

Maybe fluorescent bulbs aren't ideal for high yields and powerful cannabinoid profile, but that hasn't stopped people from making them work. If you are new to growing, can (and should) you grow weed with fluorescent grow light bulbs, like the popular t5s? 

There are, of course, limitations for any fluorescent option, but many growers with tight budgets work around these to produce great-home grown buds — especially in small spaces. 

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T5 Fluorescent Grow Lights for Cannabis

Several recent advances in fluorescent grow light technology have meant these economic fixtures do work for growing weed. 

Fluorescent Technology

You are likely already very familiar with fluorescent bulbs, as they are frequently installed in offices, malls, and large department stores.

Fluorescent light technology relies on low-pressure mercury-vapor gas-discharge within a glass tube. An electric arch shoots through the bulb to excite the mercury vapor and produce light diffused through the specially coated surface. 

Fluorescent Grow Light Efficiency

There are a few common sizes, including T5, T8, and T12 varieties. The only one recommended for the grow room is T5, as it's the most efficient with roughly 100 lumens per watt. T5s are considered high output, which is what you want for growing cannabis.

Are you growing with T5s? Begin using the cool light color option in flower, and switch out the T5 bulbs with a warm white option for flower.

T5 Grow Light Lifespan

How long do fluorescent light bulbs last? It depends on the fixture (i.e., the ballast) and the application. Energy surges from turning the lights on can significantly lower the life span. 

Although 20,000 hours is commonly cited as a standard t5 bulb's lifespan, most growers agree it's actually much lower. After only three to four grows, you might find the actual performance is significantly less. Fluorescent bulbs used in a grow light capacity have a steep degradation.

Controlling for Growth with T5 Grow Lights

Most sources recommend T5 grow lights only for use in small spaces (or as supplemental options). Light from these fluorescent bulbs doesn't penetrate the canopy well, which means the entire grow must be quite compact.

T5 lights must be placed only a few inches above the tops of your plants to ensure they provide enough light for healthy veg and flower development.

You can determine how high to hang your T5 grow lights by performing the hand test outlined here. Around four inches is best. These lights don't emit nearly as many infrared wavelengths as HID lighting, which means the risk of burning the canopy is low.

Short and Wide for T5s

If you choose to use a T5 grow light setup for the full grow (veg through flower), keep plants short and growth horizontal with a training technique like SCROG. Because a T5 isn't going to penetrate deep through the canopy, it's essential to spread the plant out horizontally for maximum impact.

Using T5 as Supplemental Lighting

What's much more common than a full-set up with T5 fluorescent bulbs is a room set up to use them only as supplemental lighting. There are much more efficient lighting options out there when you crunch the numbers (yield against watts), including both LED and HID grow light options. 

Here are a few ways T5 fluorescents can work as supplemental lighting in the grow room:

Highlight Shady Corners

If your standard grow room light isn't large enough for the number of plants you've got crammed in the grow space, you may notice a few shady corners. These plants will suffer unless they receive enough light, but maybe it's not in the budget to completely overhaul the system. Use T5 grow light bulbs to supplement HID or LED grow lights until you have the budget to buy a size-appropriate fixture.

Boost Blues

Fluorescent bulbs come in a variety of colors, but they tend to lean blue. Blue is ideal for vegging, which is why some indoor growers supplement their veg room with a few T5s. This can help transform an all-purpose LED into a much better glow for bushy vegetative growth.

Side Light for Better Light Penetration

Depending on your technique, you may find light doesn't effectively penetrate through the canopy to lower leaves and hidden colas. Add a few T5 tubes along the sides of your grow tent or room to solve for this. 

Making it Work With T5 Grow Lights 

Although commercial growers rarely rely on fluorescent grow lights as the primary fixture, that doesn't mean these bulbs have no use within a home grow. Many small-scale hobbyists have harvested an impressive yield from a grow tent hung with T5 grow light bulbs. 

Author | Chris McDonald

With two decades of expertise, Chris leads Happy Hydro in redefining sustainable gardening and delights in backpacking adventures, mind-expanding journeys, and creating memories with his loved ones.

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