Can you veg with T5 lights?

T5 grow lights have become a popular choice for indoor gardeners looking to grow healthy plants. Their versatility and effectiveness for vegetative growth has made them a staple in many grow tents and indoor grow rooms. But can T5 lights be used successfully for the vegetation stage of cannabis and other plants? Let’s take a closer look at what makes T5 lights an excellent option for the vital vegetative phase.

What are T5 Grow Lights?

T5 simply refers to the shape and size of the fluorescent tubes used in these lights. T5 tubes are 5/8ths of an inch in diameter (the “T” stands for tubular). This is smaller than the wider T8 and T12 tubes found in older fluorescent lighting systems. T5 tubes are often just called “HO tubes” because they provide high output lighting.

Some key advantages of T5 grow lights:

  • Very efficient – They put out a lot of light while using less electricity than other lighting options.
  • Run cooler than HID lights like HPS or MH.
  • Emit light in the optimum color spectrum for plant growth.
  • T5 fixtures are adaptable and can hold multiple tubes in different configurations.

The slim shape of T5s allows for many tubes to be placed close together in a single fixture, concentrating intense light output over a given area. The most common T5 setups use 4, 6, 8, or 10 tubes in a single fixture. The more tubes, the more powerful the unit.

Why Are T5 Lights Good for the Vegetation Stage?

The vegetation or “vegging” phase is the first stage of plant growth after germination. It is a crucial period where young plants are establishing roots and leafy growth under bright lighting conditions. This is before the flowering/fruiting stage, when plants need different wavelengths of light.

There are a few key reasons why T5 fluorescent lights excel at the vegetative stage:

  • Full Spectrum Light – T5s emit a balanced full spectrum, including blue and red wavelengths ideal for leafy green growth. This stimulates robust photosynthesis and biomass production.
  • High Light Intensity – T5 fixtures provide powerful illumination focused directly above the canopy. This is critical for short, compact vegetative growth before the stretching flower/fruit stage.
  • Low Heat Output – Unlike high intensity discharge (HID) lighting, T5s don’t get too hot. This prevents light stress and allows fixtures to be positioned closer to plants.
  • Energy Efficiency – Electricity costs are lower compared to growing under HPS or MH lights. And less AC may be needed to cool the grow space.

The combination of full spectrum quality, high intensity, low heat, and efficiency make T5 the top choice for many indoor gardeners during the crucial vegetative period.

How to Use T5 Lights for Vegetative Growth

If you decide T5 lighting is right for your vegetation phase, here are some tips for setting up and using T5 grow lights:

Choose the Right Fixture

Select a T5 fixture designed specifically for horticulture instead of standard office lighting. High quality grow light units are built with reflective hoods that intensify and direct light downward. They also have ballasts and components made to handle the demands of 12+ hours of daily use.

Aim for T5 fixtures holding 6, 8, or 10 tubes. These provide enough intensity for robust vegetation. Coverage depends on the height above plants, but units with 6-10 lamps often cover 2′ x 4′ up to 4′ x 4′ areas.

You can mix cool and warm white tubes to achieve a balance of blue and red wavelengths. Many units come with a combination of tubes for full spectrum light.

Hang Lights 12-24 Inches from Canopy

Since T5 lights don’t emit much heat, they can be kept close to plants to provide intense illumination. Most growers keep their T5 fixtures 12 to 24 inches above the top of the plant canopy.

Use adjustable hangers so you can easily raise lights as plants grow taller during the vegetation stage. Just make sure leaves aren’t actually touching bulbs, which can cause light burn.

Run Lights 18-24 Hours per Day

Vegetative growth excels under 18-24 hours of bright light per day. Setting up an outlet timer makes it easy to automate this lighting schedule. The high output of T5 fixtures allows them to vegetate plants even at 24 hours daily.

Some growers provide 18 hours of intense light from the T5, then 6 hours of lower intensity lighting from CFLs or LEDs. This mimics the transition from daylight to dusk and dawn.

Use Reflective Surfaces in Grow Space

Cover the walls and ceiling around your grow area with reflective surfaces. This maximizes light intensity reaching plants from all angles. Reflective films like Mylar or white paint work well. Even hanging emergency blankets can do the trick on a budget.

Provide Good Ventilation & Air Circulation

Although T5 lights don’t emit much heat, ventilation and airflow are still important in an indoor grow room. This allows you to take advantage of the full intensity without excessive heat buildup. Use oscillating fans and exhaust systems to keep fresh air moving over plants.

With good T5 coverage, ventilation, and 18-24 hour daily lighting, your plants will take off with vigorous vegetative growth.

Best Practices for Vegging with T5 Lights

Here are some key best practices that will help you get the most out of using T5 fluorescents for the critical vegetation phase:

Start Plants Under CFL or LEDs

The ultra-high intensity of T5 lights can be too much for tender, young seedlings. Start sprouts or clones under lower intensity CFL or LED bulbs. Allow them to establish some growth for 1-2 weeks before moving under the powerful T5 lights.

Use Reflectors and Rotated Bulb Positions

T5 fixtures often come with reflectors built around tubes to redirect light down to the canopy. Rotating the position of bulbs so some point straight down while others are angled can further optimize coverage.

Hang Lights Vertically for Even Distribution

When hanging multiple T5 units, position them vertically to distribute light evenly across the entire garden area. This prevents intense hot spots directly under fixtures and weaker light on edges.

Clean Bulbs and Reflectors Regularly

Dust building up on bulbs and reflectors decreases light efficiency. Wipe bulbs down every couple weeks and scrub reflectors to ensure maximum output is reaching plants.

Avoid Too Much Heat Buildup

While T5 lights run cooler than HID grow lights, heat can still build up, especially with poor ventilation. Make sure temps in the grow space don’t exceed 80°F during lights on. Add more exhaust fans and circulation if needed.

Watch for Signs of Light Stress

The close proximity and high intensity of T5 lights can occasionally cause light stress. Look for bleaching, yellowing or crispy leaves. Raise lights a few more inches if this happens.

Following these practices will optimize your T5 setup and help your plants thrive!

Ideal Vegetative Stage Duration Under T5 Lights

Just how long should you vegetate plants under T5 grow lights before switching to flowering/fruiting stage conditions? This depends on several factors:

Plant Variety & Grow Goals

– Short Bushy Plants – 2-4 weeks veg time
– Medium Plants – 4-6 weeks veg time
– Tall/Lanky Plants – 6-8+ weeks veg time

Sativas and hibiscus varieties need longer vegetation periods to promote vertical growth before beginning to flower. Indicas and short stocky varieties vegetate faster. Also consider your overall grow goals. Longer veggie stages produce higher final yields.

Space Limitations

The size of your grow room or tent limits how long you can let plants vegetate. Make sure they have space to grow taller and wider before switching to 12/12 lighting schedules.

Don’t wait until plants are crammed against walls or getting burned by lights above – transition to flowering before space maxes out.

Light Intensity & Spectrum

The more intense full spectrum light from T5 fixtures allows for faster vegetative growth. With robust blue/red spectrum output, plants often veggie 25-50% quicker under T5s than other lighting like CFLs.

Container Size

For container gardens, the volume of soil available to roots impacts vegetative time. For example, plants in 3-5 gallon pots veggie faster than those in 1 gallon containers. Upgrade pot sizes if vegetation seems slow.

Aim for 4-8 weeks in veggie stage based on these factors. Track plant growth rates to nail down ideal timings.

Troubleshooting T5 Grow Light Issues

While T5 lights are very effective for vegetative growth, you may occasionally run into problems. Here are some common issues and fixes:

Problem: Slow Vegetative Growth

  • Try lifting lights closer to canopy
  • Increase temps to 70-80°F
  • Check bulb age – replace older tubes
  • Reflectors and circulation may need improved

Problem: Leaf Burn or Bleaching

  • Raise light height above plants
  • Reduce photoperiod to 16-18 hours
  • Add calcium-magnesium supplements
  • Ensure temps under lights don’t exceed 80°F

Problem: Leggy, Spindly Growth

  • Increase light intensity with added tubes
  • Lift reflectors closer to bulbs to concentrate light
  • Reduce photoperiod to 20 hours or less

Problem: Bulbs Burning Out Frequently

  • Ensure ballast is rated for T5 lighting
  • Reduce photoperiod to 18 hours max
  • Add more circulation fans in grow space
  • Don’t exceed recommended bulb life – change bulbs every 6-12 months

Monitoring your grow and making adjustments will resolve most issues with T5 fixtures or performance.

Using Supplemental LEDs or CFLs with T5 Lights

While T5 fluorescent tubes provide highly effective vegetative lighting, some indoor gardeners choose to augment these fixtures with supplemental CFL or LED bulbs. Here are two good ways to incorporate supplemental lighting:

Add Flowering Stage LEDs

Hang LED grow lights matched to the flowering/fruiting stage over sections of plants that are transitioning from veggie growth. The red spectrum LEDs prepare plants for maturation while central T5s remain focused on vegetative growth of younger plants on a different schedule.

Plug in CFLs for Additional Grow Space Lighting

Standard spiral compact fluorescent light bulbs can provide economical supplemental lighting. Plug in CFLs between the T5 fixtures to eliminate darker spots in the grow space and ensure consistent light coverage across the entire garden.

When using supplemental lighting, make sure intensity, photoperiods, and spectrum are tailored to each plant’s specific growth stage. Get the best outcomes by matching the right lighting technology to vegetation vs. flowering needs.

Sample T5 Grow Lighting Setup

Here is an example of a high quality T5 grow light setup that provides excellent coverage for vegetative growth:

Key Components

– 2’x4′ Grow Tent
– 2x – “T5 4ft. 8-Tube Fixture” – Mix of 6500K & 3000K bulbs
– 2x – “T5 2ft. 4-Tube Fixture” – Mix of 6500K & 3000K bulbs
– Adjustable Light Hangers
– Mechanical Timer
– Exhaust Fan & Circulation Fan
– Mylar Reflective Sheeting


The 4000K 8-tube fixtures are mounted vertically at each end of the tent to provide full coverage across the 2′ x 4′ space. Fixtures are hung about 18 inches above canopy level on adjustable hangers.

The supplemental 2500K 4-tube units are horizontally mounted in the middle to boost intensity for the vegetative stage. All bulbs are oriented for optimal reflector efficiency.

Six inch exhaust fan ducted to a carbon filter maintains temperature and airflow. Clip fans circulate air within the tent.

The mechanical timer ensures 18 hours daily photoperiod for vegetation stage plants. Mylar sheeting creates a reflective surround.

This setup delivers optimized spectrum, intensity, and coverage for robust T5 vegetative growth!


T5 fluorescent grow lights are an extremely effective and efficient option for the vital vegetation phase of plant growth. Their full spectrum light, high intensity, low heat, and electrical efficiency make them ideal for indoor gardens. Positioning T5 fixtures 12-24 inches above the canopy and running photoperiods of 18-24 hours will maximize vegetative growth rates. Just make sure to monitor for any signs of light stress. Supplementing with CFLs or flowering stage LEDs can provide added coverage and flexibility in grow room setups. With a properly configured T5 lighting system, indoor gardeners can achieve short, bushy, vibrant veggie growth and give plants the best start before flowering.

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