GroMax T5 PureUV Bulbs for Improved Quality and Yield
For cannabis growers seeking to elevate their harvest’s quality and potency, adding UV lighting to the grow room is a must-have. While traditional grow lights (such as HPS, LED, and CMH) focus on delivering essential red and blue wavelengths, ultraviolet (UV) light can trigger enhanced resin, terpene, and THC production in cannabis plants.
My Switch from UVA LED to T5 UVB
I previously owned expensive LED bar lights (primarily UVA) for about two years. After reading numerous reports from experienced cannabis growers on the superior results gained by adding UVB (rather than UVA) and seeing how most LED-based UV systems underperformed in this regard, I decided to give lower-cost T5 UVB bulbs a try. Once I completed a single grow cycle under T5 UVB, I noticed a significant jump in trichome production—along with very high THC levels. The improvement was so pronounced that I immediately sold off my UVA LED bars and have stuck with T5 UVB ever since. Getting rid of those LED bars also eliminated a major source of extra heat in my grow, making the switch both decisive and fast.
This article explains the science behind UVA vs. UVB, why a 4-Foot T5 Fluorescent Grow Light Fixture – $44.95 along with a GroMax 48″ PureUV T5 Fluorescent Bulb – $13.97 each or a 4-pack GroMax 48″ PureUV T5 Fluorescent Bulbs – $99.50 is both cost-effective and possibly the best way of increasing the potency of your cannabis, and how to integrate UVB lighting into your setup current. A typical plant canopy size of 5’x5′ requires two – 48″ T5 Florescent Lighting Fixtures and you will also need a PureUV T5 Floresent Bulb for each lighting fixture.
Key Benefits of GroMax T5 Bulbs for UVB Lighting
- Increased Potency: UVB light induces a noticeable increase in trichome and resin production, boosting THC levels and enhancing terpene profiles more effectively than UVA.
- Cost-Efficient: T5 fixtures and UVB tubes (like the GroMax 48″ T5 bulbs) are significantly cheaper than comparable UVA LED setups.
- Short Run Times: UVB only needs to run for a few minutes each hour—drastically cutting energy use compared to UVA lights that run for 6+ hours daily.
- Low Heat: Because the UVB tubes operate briefly, they contribute minimal heat, which helps maintain an ideal grow room environment without extra cooling costs.
UVA Light (320–400 nm)
Positive Effects on Cannabis
- Longer Run Times: UVA lamps typically need to run for multiple hours per day and can generate a lot of heat during operation.
- Milder Stress: UVA causes less immediate stress to plants than UVB. Overexposure, however, can still damage plant cells over time.
- Moderate Potency Boost: Can enhance cannabinoid and terpene levels but usually not as significantly as UVB.
Mitigating UVA’s Potential Harm to Cannabis and Humans
- Humans: Skin Cancer and Retinal Damage to the Eyes: Can occur with long term exposure to UVA lighting, limit exposure time and wear protective clothing and eyeglasses that filter UVA rays.
- Cannabis: Leaf Damage: Prolonged UVA can stress plants, causing minor leaf damage or slower growth if levels are too intense. Reduce exposure duration and the distance from the plant canopy to the UVA lighting should signs of stress occur.
UVB Light (280–320 nm)
Positive Effects on Cannabis
- Short Run Times: UVB is generally used for only a few minutes each hour (up to 10–12 minutes) to achieve beneficial effects without causing severe damage especially when the plant is still growing. Never exceed 15 minutes for the UVB light duration during a one-hour period and limit to about 6 hours a day during the middle six hours of time.
- Stronger Stress Response: UVB light induces a noticeable increase in trichome and resin production, boosting THC levels and often enhancing terpene profiles more effectively than UVA.
- Proven Potency Enhancer: Studies show higher cannabinoid levels—particularly THC—when cannabis plants receive controlled UVB exposure.
Mitigating UVB’s Potential Harm to Cannabis and Humans
- Humans: Skin Cancer and Retinal Damage to the Eye: UVB is more energetic than UVA and can cause immediate sunburn (erythema), eye injuries like corneal burns, and contribute to an increased risk of skin cancer risk in shorter periods of time. Short bursts of UVB are can still harm unprotected skin and eyes quickly. Do Not enter the grow tent when UVB Lighting is turned on, I recommend limiting your exposure by 100%. I use a cheap red flashing light connected to the same power strip as my T5 UVB Lights to let me know right away if the lights are in use should I open the tent during operation. You must turn off UVB lighting before working inside of your tent or you could be at serious risk of skin cancer when exposed to UVB lighting repeatedly over time. Try to schedule plant checks or maintenance when UVB lights are off.
- Cannabis: Leaf Damage Overexposure can cause RNA damage, leading leaf deformities and missing leaf “fingers”, or even stunt your plants growth. Keep exposure times under 12 minutes and never use more then 15 minutes of UVB lighting within an hour time and limit to 6 exposures a day during the peak growing hours (3 hours after the main lights come on and 3 hours before the main lights go off). If your plant shows signs of stress you can reduce the lighting exposure and possibly move the UVB lights farther from the plant canopy.
Why UVB Lighting Improves Cannabis Quality
When cannabis plants sense UVB, they build thicker resin layers and more trichomes to protect themselves. This adaptation directly increases THC content and can also enhance terpene profiles, resulting in more aromatic and flavorful buds. In many instances, UVB lighting leads to a “frostier” appearance and stickier texture, reflecting the extra resin production.
Implementing T5 UVB Lighting in Your Grow Room
- Fixture Placement: For a 5′ × 5′ grow space, use two or three four-foot T5 UVB fixtures (fitted with GroMax 48″ T5 bulbs) above the canopy. Position them about 18–24 inches from the tops of the plants.
- Exposure Time:
- Start with 1–5 minutes of daily UVB exposure at the beginning of flower (or even in late veg).
- Gradually increase to 10–12 minutes per hour by around the 5th week of flowering, monitoring plants for signs of stress.
- Never exceed 15 minutes of UVB light per hour.
- Timing: Schedule UVB to come on roughly 3 hours after your main lights turn on. Cycle it on for those brief intervals (once per hour for a total of ~6 hours a day). Finish a few hours before the main lights go off.
- Monitor Plant Health: Watch for leaf curling, discoloration, or missing “fingers” on leaves. These are signs of overexposure to UVB. If visible stress occurs, reduce the UVB run time or increase the distance between bulbs and plants.
- Safety Measures: UVB light is harmful to skin and eyes. Wear protective eyewear and minimize direct exposure when working around the fixtures.
UVA vs. UVB: Why T5 UVB Outperforms UVA LED
- Higher Potency Gains: UVB has been shown to increase THC content more directly than UVA.
- Less Heat Generated: You’ll run T5 UVB bulbs for just minutes per hour, reducing the heat in your grow tent and energy costs at the same time.
- Lower Cost: GroMax 48″ T5 Light Fixtures and PureUV Fluorescent Bulbs together cost less than half the price of UVA LED light bars.