The role T5 grow lights play in the grow room has been overlooked for quite some time. Sure, T5s are perfect for growing herbs and helping seedlings and clones reach the vegging stage. They can even be great as supplemental lights to HIDs and LED grow lights. But did you know a T5 light can grow fruiting plants — like citrus fruits and cannabis — from seed to harvest?
There’s a lot of conflicting information out there regarding T5 grow lights and their effectiveness in the grow room. That’s why we explored T5 lighting and put together this guide to help you incorporate T5 grow lights into your next grow.
Before we explore their benefits, though, let’s dig into the science behind T5 grow lights.
- Color Temperature and Wavelengths
- Lumen Output and PAR
A T5 grow light is a grow light that gives off light via T5 fluorescent light bulbs, just like HIDs do with HPS/MH bulbs, and LEDs with diodes. The T in its name represents the tube shape of the light bulb, and the 5 stands for the ⅝ in diameter of the bulb itself.
In order to give you light, electricity creates energy that heats gas (argon) and metals (mercury) inside of the bulb. However, unlike HIDs and LEDs, T5 lights produce UV light.
UV rays can’t be utilized by plants in high amounts, so T5s are coated inside with phosphors. The phosphor coating reacts with the UV rays, buffers them, and helps turn them into the light your plants use. Depending on the combination of phosphors, you’ll get different light temperatures, and subsequently, different wavelengths of light.
Due to their chemical makeup, the light created by T5s doesn’t produce a high amount of heat, either. That makes T5 grow lights both safer and more energy efficient than HIDs. This is due to two reasons:
The mercury, argon, and phosphorus in T5 bulbs don’t require a lot of energy to produce a light’s full potential. In turn, the chemicals inside will not produce a lot of heat that will radiate from the bulb. The salts, gases, and metals in HID lights need more energy to heat up and produce light to its full potential. That can be dangerous if you’re not paying attention to how high your plants grow.
It takes much less energy to run a single T5 bulb than an HID. T5 grow lights come in 2ft 24w bulbs and 4ft 54w bulbs, so even four-bulb T5 lights will take only 216w to grow three to four trays of clones. Compare that to HIDs that take at least 250 to 400w to run a single bulb — and that’s not mentioning the energy that ventilation equipment will eat up trying to cool your growing area.
T5 light reflectors are lightweight and simple in design. They have angled reflective backing for reflecting light in multiple directions. The ballast is tucked into the reflector itself, and the bulbs have a locking fixture instead of twisting them into a socket.
Seems simple, right? That’s because it is.
Different sized reflectors give you different strength and coverage areas. As such, the amount of space you have available for your garden will dictate the type and number of plants you’re able to grow.
To make this point clear, below are some common reflector sizes and their lighting capabilities at a recommended 12 inches above plants (more on height recommendations in a little bit).
24w are around 2ft x 6in and can give you ~2ft x 1.5ft light coverage.
54w are around 4ft x 6in and capable of ~4ft x 1.5ft light coverage.
These reflectors are the same size as single-bulb reflectors. That said, they offer different light coverages.
24w are capable of giving you ~2.5ft x 2ft light coverage.
54w can give you ~4.5ft. x 2ft light coverage.
Usually only available with 54w 4ft bulbs, which measure around 4ft x 13.25in.
These reflectors can give you around 4ft x 14in of light coverage.
Also only available with 54w 4ft bulbs, and measure 4ft x 2ft.
These reflectors can give you around 4ft x 2.5ft of light coverage.
While energy efficient, T5 grow lights can sometimes be spatially inefficient, taking up more room in your grow than anticipated. The more coverage and power you need out of a T5, the larger of a reflector you need. This is important in figuring out what sort of T5 you’ll need and what you can use to grow the plants you want.
T5 grow lights, like any grow light, are capable of giving your plants the wavelengths and lumen output they need to grow. However, finding a T5 for your plants that’s powerful enough and has the right wavelengths of light may not be as simple as it would be with other grow lights.
Simply reading a product name like “Yield Lab Complete 54w T5 Four-Bulb Fluorescent Grow Light Panel (6400K)” can leave you wondering what you can expect from it. If you’re not familiar with grow room terminology, this can leave you asking, “Will this light veg my plants? Will it flower them? How strong is this T5 anyway?”
Understanding T5 lights can be confusing. That’s why we broke down the terms you need to know so you can choose a grow light with the right strength and wavelengths for your plants.
Like with any grow light, you’ll first want to look into the wavelengths of light your plants will receive from a T5. That’s all found in the color temperature your light has.
The color temperature of any grow light is an accumulation of various wavelengths of light, and that color is measured in Kelvin, or K.
6400k lights give off a light that looks similar to an MH bulb, which is a cool color temperature containing blue wavelengths of light. These are what you need for growth of branches and leaves through the vegging stage.
2700k lights give you light that’s similar to HPS bulbs, which is more of a warm color temperature that has red wavelengths of light. These are what you need to flower your plants though harvest.
Like LEDs, T5 lights also come in individual wavelengths. Bulbs like the PowerVeg have colored phosphorus coating to target and give your plants individual wavelengths of light. These include blue (420nm), red (633nm), and violet (660nm) light, all of which stimulate various types of growth throughout your plant. There are also T5 lights that target UVA and UVB wavelengths of light, which can be helpful for plant strength, resin growth, and terpene production.
Once you know what color temperature you’re looking for, it’s time to see how intense your lights need to be in order to grow.
A light’s brightness is measured by the amount of lumens it gives off. Of course, plants don’t absorb all of the bright light they receive, so it’s important to take into account the strength of a light, which is measured in PAR (Photosynthetically Active Radiation).
T5 lights typically don’t include a PAR rating when you purchase them. Even then, we’ll show you how to get a good idea of a T5 light’s PAR rating through its total lumen output. To illustrate this, we’ll compare 54w T5 grow lights to Yield Lab 400w HPS and MH grow lights.
Let’s start with the HIDs:
400w MH bulbs have a lumen output of 36,000 lumens with a PAR range of 294 to 416 at 18 inches above plants. This is the minimum amount of lumens we’ll need for plant growth.
400w HPS bulbs have a lumen output of 55,000 lumens with a PAR range of 310 to 534 at 18 inches above plants. This lumen output is more than capable of plant growth, so we’ll shoot for this with our T5 light.
400w lights have an average footprint of ~3ft x 3ft.
Now we’ll plug in our T5 grow light specs:
Each bulb in a 6400k 54w T5 grow light is around 5,000 lumens. With an eight-bulb fixture, you can reach the same 36,000 lumen output of a 400w MH bulb, with a footprint of 4ft x 2ft at 12 inches above plants.
Each bulb in a 2700k 54w T5 grow light is usually around 4,950 lumens. That means you’ll need a 12-bulb fixture to keep up with the 55,000 lumens a 400w HPS lamps give off. You’ll also get a footprint of 4ft x 2ft with these lights at 12 inches above plants.
There are two things to notice here. First is the fact that you can get the same lumens from a T5 as you would with an HID. Second, while the PAR rating on HIDs may be greater, their footprint is smaller, and the light has to be further away than if you’re using a T5. Though T5 grow lights lack the high PAR of HIDs, they offer a softer intensity by being closer to plants — this puts their PAR close to an HID's PAR.
Before we start figuring out how to choose the right T5 grow light for your garden, let’s do a quick review of what we’ve learned so far:
T5 grow lights come in 2700k (blooming) and 6400k (vegging) color temperatures that offer wavelengths of light to promote various stages of growth, like HPS/MH bulbs.
T5 fluorescent bulbs come in 2ft (24w) and 4ft (54w) sizes, and reflectors for those lights come in single, dual, 4-bulb, 8-bulb, and 12+ bulb sizes.
T5 lights also come in isolated wavelengths of light like blue, violet, red, and UVA/UVB.
Due to their chemical makeup, they’re able to run at much lower temperatures than HIDs. That means they don’t give off as much heat as HIDs and don’t take nearly as much energy to run.
Though the lumen output of any single bulb is relatively low (4,960 to 5,000 lumens/bulb), their total lumen output is comparable to HIDs.
The PAR ratings of T5 grow lights are on the lower end of their HID counterparts’. However, this is still plenty of usable light to grow with.
Now that you have the foundations of what to look for in a T5 grow light, let’s find the best one for your grow room.
Before we dive head-first into lighting suggestions, we should start by first setting reasonable expectations for our T5 grow lights.
More Lumens = Bigger Reflectors and Less Space in Your Grow Room: Our first piece of advice is to be mindful of your lumen and PAR requirements. As we’ve mentioned, T5 lights have a lower PAR than HIDs, which means the useful light they give off isn’t as strong. The more lumens and PAR you need out of a T5 grow light, the more bulbs you’ll need, which means bigger reflectors.
A 600w HPS bulb, for example, gives off 99,000 lumens, so it would take about twenty 54w T5 fluorescent light bulbs to match the lumen output you need. That would require two 12-bulb fixtures that measure around 4ft x 2ft each, which is going to take up a good amount of space in your grow room.
Less Light Penetration: Collectively, T5 fluorescent bulbs give you intense lumen output. Individually, though, they have less lumens per bulb. That means the light penetration across your light — and subsequently, over your canopy — is lower than an HIDs.
This isn’t a big issue to conquer, but you’re going to need to do two things to get the penetration your plants — especially fruiting plants — need to grow:
Train your plants to grow outward. Tall leaves block lower branches from receiving light. With HIDs this isn’t a big deal because their intensity penetrates plants with enough strength to help shaded branches grow. Unfortunately, T5 grow lights don’t have that type of intensity, so taller, more stacked plants have a hard time growing. Pruning and training your plants to grow outward leave more foliage exposed to light. When hung at 12 inches above trained plants, T5 lights can penetrate leaves and stimulate plant cells needed for vigorous growth.
Limit your plant count. In order to maximize your plants’ growth potential under T5 lights, you may need to scale back the number of plants you want to grow. Remember that while T5 lights can cover a large area, their PAR is relatively low, so they’ll need to be closer to your plants than with other lights. That means you won’t be getting the same intense coverage you get from other lights, which will ultimately limit how many plants will thrive per light.
It’s important to keep your yield expectations reasonable. Because T5 grow lights aren’t pumping out the same PAR as other grow lights, your yields will naturally be lower than with other lights.
Don’t worry, though — you’ll still get great buds, fruits, and flowers with tons of flavor. Moreover, you’ll be growing them in less environmentally stressed conditions, which also benefits growth.
T5 grow lights are great if you’re looking to harvest fruiting and non-fruiting plants without having to deal with intense temperature and environmental issues. The difference is that the yield will be lighter — in both physical size and overall harvest size — due to a lack of intensity.
Finding the right T5 grow light for your garden can be done in one of two ways. You can choose your light by figuring out how many lumens your plants need, or you can choose your T5 based on your spatial restrictions. The first is probably the most reliable measurement, but when it comes to T5 lights, the second method can be just as effective.
Calculating Lumen Requirements
Most plants need an average of 5,000 lumens of light per square foot (sqft) to grow, which is what you should aim for. They can survive off of 2,000 lumens and thrive off of 7,500 lumens. Take stock of your plants and figure out how many lumens of light they’ll need per square foot.
If they need an average or high amount of lumens for fruiting plants and buds, you’ll want to go with a 54w T5 light.
A 54w light can give you the sweet spot of 5,000 lumens.
When you need a minimal amount of lumens for seedlings, clones, and herbs, 24w bulbs will be just fine.
Once you know the wattage and the lumens per square foot your plants need, you can calculate the total amount of lumens you’ll need in your grow area.
For example, if you find that you need to cover a canopy that’s 3ft x 3ft with 5,000 lumens/sqft, you’ll need a total lumen output of at least 45,000 lumens. That means you’ll need at least nine 54w T5 bulbs to get your plants where they need to be. Thankfully there are fixtures like the DoubleLux 4ft 12-Bulb T5 Fluorescent Light that have the ability to grow your plants with more intensity than you need, which is great when it comes to T5 lights.
All T5 grow light reflectors are different sizes, so you’ll need to make sure the T5 you need can fit in the space you’re growing in.
Whether you’re using T5 lights as a supplemental light or your main light source, they’ll require at least 2 to 4ft of space in any direction due to their bulb size. This may create some problems depending on the size of your growing area.
A four-bulb 54w T5 grow light, for example, measures around 4ft x 13.25in. If you don’t have 4ft of room to work with, you’ll need to downsize to a 2ft 24w T5 grow light. This will reduce the overall lumen output of the light, which will limit the plants you’re able to grow.
Even with all the information at your fingertips, it can still be hard choosing the right T5 light for your needs. That’s why we tested a number of T5 grow lights to see what works best for different grow setups.
Single and Dual-Bulb T5 Grow Lights
Single and dual-bulb T5 grow lights will give you enough lumens to propagate a tray of seeds, grow a tray of clones and seedlings, and grow a few herbs. These types of T5 fluorescent lights don’t put out tons of energy, but that’s what makes them great for smaller plants.
HIDs can overheat smaller plants like clones and seedlings, and LEDs might be too intense for young plants. T5s give off a gentle yet effective amount of light to plants.
Single-bulb 24w lights are capable of giving you 2,200 lumens, and dual-bulb lights can give you up to 4,400 lumens. The footprint would be around 2ft x 5.5in at 12 inches above your plants.
Single-bulb 54w lights can give you around 5,000 lumens, with dual-bulb lights offering 10,000 lumens of light. The footprint would be around 4ft x 5.5in at 12 inches above your plants.
Recommended Grow Light: Yield Lab Complete 24w 2-Foot Dual-Bulb T5 Fluorescent Grow Light Kit (64000K)
Four-Bulb T5 Grow Lights
Four-bulb T5 lights pump out good amounts of lumens. They’re great for growing leafy greens like spinach, lettuce, as well as plenty of herbs and microgreens. For propagation purposes, these plants can grow at least two to four trays of clones or seedlings with ease. To figure out the size of the system you’ll need, you’ll just have to decide how many greens, clones, or seedlings you’d like to grow.
Four-bulb 24w T5 fluorescent lights will give your plants a total of 8,800 lumens. The footprint would be around 2ft x 14in at 12 inches above your plants.These can grow one to two leafy greens and up to two trays of clones.
Four-bulb 54wT5s can give you up to 20,000 total lumens of light. The footprint would be around 4ft x 14in at 12 inches above your plants. This is great for three to four leafy greens and up to four trays clones.
With up to 20,000 lumens, this gives you at least 5,000 lumens per square foot — that’s plenty of light for delicious greens and starting clones/seedlings off virtually stress-free.
Eight-Bulb T5 Grow Lights
When we get to eight-bulb T5 lights, we’re starting to bridge into serious lighting. In fact, these lights and larger are only available in 54w options.
These T5 grow lights can give you up to 40,000 lumens of light at 12 inches above your plants. That’s more than a 400w MH grow light, so you know these lights are putting out some serious lumens.
The light footprint of an eight-bulb 54w T5 light is at least 4ft x 2ft. That’s enough space and intensity to grow one small flowering plant, more than five trays of clones, leafy greens, and vegetables like radishes and cucumbers.
Not only do these lights rival 400w MH grow lights, they provide an even PAR output across your plant canopy. Where other grow lights give your plants uneven lighting, this T5 will give your plants an even amount of light, putting less stress on your plants.
12+ Bulb T5 Grow Lights
When you start working with these T5 lights, you’re going to be giving your plants at least 60,000 lumens. That means you’re pumping out the same amount of lumens as a 400w HPS bulb and almost double the amount of lumens a 600w MH bulb gives off. With that amount of power, you’ll be able to grow at least one to two flowering plants like small citrus and cannabis plants.
The light footprint of these T5s starts at around 4ft x 2.5ft at 12 inches above your plants. That means these lights can light a 4ft x 2.5ft canopy for a compact harvest of fruits, flowers, buds, or vegetables.
For people growing greens and herbs as well as caring for clones, these lights are great if you plan on farming plenty of them.
The great thing about such large lights is that they can — and usually are — used in conjunction with other large lights. This helps illuminate large growing areas, harvest multiple fruiting plants, and help mother plants (plants harvested and regrown to take clones from) stay alive.
Recommended Grow Light: Agrobrite T5 648W 4' 12-Tube Fixture with Lamps (6400K)
Ultimately, T5 grow lights are surprisingly powerful and extremely useful throughout all stages of growth. Whether you’re building leaves, branches, flower buds, or fruit, T5s are extremely versatile. Not only will they grow what you need, T5 fluorescent lights will grow your plants with a fraction of the heat an HID would give you. That helps give your plants a stable environment and saves you electricity.
It’s important to understand the limitations of T5 grow lights, though. Their PAR output is limited, and even when hanging lights 12 inches above plants, it’s a good idea to train plants to grow outward if you plan on growing healthy fruiting plants — otherwise T5 lights will be ineffective.
Still, with a small bit of plant training and the right light, you’ll be able to churn out high quality, heat-free harvests all year using T5 grow lights.
1. Why would I use a T5 light over an HID or LED grow light for indoor growing?
T5 grow lights give you a gentle yet effective light that HIDs and even most LEDs can’t give you. Whether you’re growing fragile plants like seedlings and herbs, or hearty plants like leafy greens and cannabis, T5s give your plants the necessary wavelengths and intensity without overwhelming them.
The issue with HIDs and LEDs is that even at their lower strengths, their power is usually too much for young, sensitive plants like seedlings and herbs. HID grow lights give young plants lots of heat energy that can fry them, and LEDs can bleach or underwhelm young plants — this can lead to failure in the grow room. The UV light produced in T5 lights creates a lot less physical heat than HIDs, and the phosphors coating of T5s help buffer the intensity of light your plants receive while giving them the wavelengths of light they need.
To be fair, if you’re looking to grow monster cannabis plants or big fruit trees, you’ll need a more intense light. However, if you want to grow one or two fruiting plants, care for seedlings and clones, or grow herbs and veggies, T5s will give you the harvest you want with little to no light stress.
2. What sort of plants can you grow with T5 grow lights?
T5 grow lights can help grow nearly any type of plant you can think of. From succulents to herbs, veggies to fruiting and flower plants, T5s can grow virtually anything — within reason, that is. While you can grow a whole host of plants with them, not every plant will respond to every T5 light.
Here’s an idea of what you can grow depending on the type of T5 grow light you’re working with:
Single and dual-bulb 24w and 54w T5s can grow small herbs, one to two trays of clones/seedlings, and microgreens.
Four-bulb 24w and 54w T5 lights can help you grow leafy greens, three to four trays of clones/seedlings, and small veggies like cucumbers and radishes.
Eight-bulb 54w T5 fluorescent lights can grow one small fruiting plant*, five or more trays of clones/seedlings, leafy greens, and veggies like tomatoes.
12+ bulb 54 T5s can grow one to two fruiting plants*, multiple trays of clones/seedlings, and veggies and herbs, as well as keep mothering plants alive.
*Fruiting plants will require training to produce a quality harvest.
3. How high should I hang T5 lights over my plants?
When it comes to hanging your T5 grow lights, you’ll want to hang them around 12 to 18 inches above your plants. Unlike HIDs that you’d need to hang 18 to 20 inches above plants, and LEDs that need 20 to 24 inches of space above plants, T5s don’t have the same intensity as other lights. That lack of intensity leads to less light penetration and absorption from your plants.
Above 18 inches, T5 lights become ineffective because they can’t send as much of their energy to plants like HIDs or LEDs. That’s why you’ll want to hang them 12 inches above your plants, with more intense T5s up around the 18-inch range.
Contrary to popular belief, you can’t place T5 lights closer than five inches to their canopy. While T5 grow lights give soft light, it’s important to keep in mind two things:
Minimal heat doesn’t mean 0 percent heat. T5 grow lights still give you a little bit of heat, so make sure your canopy isn’t too close. T5s that are too close will still burn plants.
UV light, while buffered by phosphors, is still emitted from T5s. If plants are too close, they’ll receive much more UV wavelengths than they would further away. That can lead to bleaching, which will hinder growth.
When growing with T5s, start at 12 inches above your plants and work from there. If you see plants start to curl up, raise your lights until they start opening back up. If your plants start to stretch out and become weaker, lower your lights, but make sure not to lower them to five inches above your plants.
4. How much power will a T5 grow light use in my grow room?
This one’s vital because T5 lights may not generate lots of heat, but they can still use up a good amount of energy. Single, dual, and four-bulb lights have a wattage range of 24w to 216w. That’s a pretty minimal wattage range in the grand scheme of things. Once you start getting into 8+ bulb lights, though, things start to add up.
The easiest way to figure out how much energy you’ll be using with a T5 grow light is to take the wattage of each bulb and multiply it by the number of bulbs that are in the system. Using this formula, here are a few examples of energy usage per light:
(24w) X (4 bulbs) = 96 watts
(54w) X (4 bulbs) = 216 watts
(54w) X (8 bulbs) = 432 watts
(54w) X (12 bulbs) = 648 watts
(54w) X (16 bulbs) = 846 watts
These values can be surprising since we’ve been saying all along that T5s are more cost efficient than HIDs. Don’t worry, though, they still are.
Say we need an eight-bulb light, which will draw 432w of energy. Sure, a 400w MH light would draw less power by itself. That said, a 400w MH light gives off a lot of heat, which you’ll need to mediate with a fan — specifically, a high output fan, which draws power, too. Even a small fan like the Yield Lab 4 Inch Pro Series Fan uses up 60w of power. That means you’d actually use 28w more trying to use an HID instead of going with a T5.
For smaller grow tents and grow rooms with a limited number of plants, T5s are more than capable of growing your plants from start to finish without using up high amounts of energy like their HID counterparts.
5. How many T5 lights do I need for my growing area?
Figuring out the number of T5 grow lights you need for your plants all comes down to the lumens they’ll need. This is pretty easy, especially if you keep in mind that plants need 2,000 to 5,000 lumens per square foot.
Smaller veggies, clones, and seedlings need around 2,000 lumens/sqft.
Leafy greens and medium-sized veggies need 3,000 to 4,000 lumens/sqft.
Flowering plants are going to need 5,000+ lumens/sqft.
From there, take the area of the canopy you want to light and multiply it by the lumens needed. The number you end up with will tell you how many lumens of light you need.
For example, say your canopy measures 4ft x 4ft. If you’re growing a flowering plant, you’ll want at least 5000 lumens/sqft.
4ft x 4ft = 9 sqft
(16 sqft) x (5,000 lumens/sqft) = 80,000 lumens needed
All you have to do is find a light capable of giving you the necessary lumens.To do that, all you have to do is take the lumens of each bulb and divide it by the total number of lumens needed. This will tell you how many bulbs you’ll need of a particular color temperature.
54w 6400k (growth) bulbs have a lumen output of 5,000 lumens each, while 2700K (flowering) bulbs have an output of 4,960 lumens — thankfully they’re around the same size. That makes these measurements a lot easier to do, so let’s get to it.
(80,000 lumens needed) / (5000 lumens per bulb) = 16 bulbs needed
Then we’ll just find fixtures to fit that. We could use a 16-bulb fixture, but for coverage and intensity purposes, it’s better to go with two 8-bulb T5 grow lights.
With that in mind, we also have to understand the size of these lights and make sure they work for our grow room. For example, if we’re using two eight bulb T5 lights, you’re looking at a total size of either 8ft (L) x 2ft (W) or 4ft (L) x 4ft (W). Configuration is key with grow rooms like these, so make sure you have the room in your growing space to fit the lights you need inside.