Why UV & IR Wavelengths Matter in Flowering
UV and infrared wavelengths operate outside the visible PAR spectrum yet profoundly influence plant biochemistry. UV radiation mimics high-altitude stress conditions, prompting plants to produce protective resins and secondary metabolites. Far-red infrared activates the Emerson Effect, accelerating photosynthesis efficiency when combined with deep red light—delivering measurable yield improvements without increasing primary wattage.
The Science Behind Supplemental Wavelengths
UV and IR supplementation addresses what full-spectrum LEDs inherently lack: wavelength precision at the spectrum's extremes. UVA wavelengths (365-395nm) penetrate surface tissues to trigger trichome development, while far-red infrared (730nm) regulates phytochrome responses that control flowering initiation and stem elongation.
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UVA Stress Response (365-395nm): The
AC Infinity Ionbeam U2 and
U4 models deliver precise dual-wavelength UV that stimulates plants to produce protective compounds—translating to denser trichome coverage and enhanced aromatic complexity without tissue damage when properly timed.
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Far-Red Photomorphogenesis (730nm): Infrared supplementation extends effective photoperiod by accelerating the transition from vegetative to flowering states. The
Medic Grow UV + FR Bar combines both wavelengths in a single 100W fixture, offering integrated control over flowering triggers and resin production.
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Targeted Deployment Timing: Professional cultivators deploy UV during the final 2-4 weeks of flowering for 2-4 hours daily, while far-red runs continuously to maintain the Emerson Effect. This staged approach maximizes secondary metabolite production without compromising photosynthetic efficiency during earlier growth phases.
Matching Supplemental Bars to Your Primary Lighting
Supplemental UV and IR bars integrate seamlessly with existing LED systems but require strategic sizing to avoid overexposure. The goal is targeted enhancement, not spectrum flooding—calculate 5-10% of your primary wattage as a starting guideline for supplemental output.
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Compact Tent Systems (2x2 to 3x3): The
Spider Farmer UV30 & IR16 Bar Set (23.6") pairs perfectly with 200-300W primary lights, delivering 60 UVA diodes and 44 infrared LEDs without overwhelming smaller canopies. Its compact form factor mounts directly to existing fixtures via included brackets.
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Standard 4x4 to 5x5 Spaces: Scale up to the
Spider Farmer UV60 & IR30 Bar Set (35.4") for 400-600W primary systems. Its 120 UV diodes and extended length ensure even distribution across larger canopies, particularly when positioned perpendicular to main light bars.
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Commercial & Multi-Bar Arrays: Operations running
commercial LED fixtures above 600W benefit from the
TotalGrow UVA 30W Bar or multiple
HLG 30 UVA bars distributed across the canopy. ETL certification and daisy-chain capability make these ideal for facilities requiring scalable, code-compliant supplementation.
Maximizing Results with Controlled Exposure
UV and IR supplementation is not a "more is better" technology—strategic timing and intensity control prevent photoinhibition while maximizing beneficial stress responses. Integrate supplemental bars with programmable
controllers for precise scheduling.
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Phased Introduction Protocol: Begin UV exposure at 50% intensity during week 5-6 of flowering, gradually increasing to full output by week 7. This acclimation period prevents shock while building tolerance for maximum final-week resin production.
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Daily Exposure Windows: Limit UVA exposure to 2-4 hours during the middle of your primary light cycle when photosynthetic rates peak. Far-red can run continuously or activate during the final hour to accelerate the shade-avoidance response, promoting tighter internodal spacing.
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Environmental Integration: Combine supplemental lighting with optimized VPD (1.2-1.4 kPa during late flower) to amplify secondary metabolite production. Monitor leaf surface temperature—UV bars generate minimal heat but should be positioned 12-18" from canopy tops to prevent localized stress. For guidance on optimizing your entire lighting strategy, explore our article on
how UVB affects terpenes and improves harvest quality.
Frequently Asked Questions
What's the difference between UVA and UVB wavelengths for cultivation?
UVA (365-395nm) is safer for prolonged exposure and primarily drives resin production through mild stress responses, while UVB (280-315nm) delivers more intense radiation that can damage plant tissue if misapplied. Most supplemental bars use UVA because it provides significant metabolite enhancement without the safety protocols required for UVB. Commercial cultivators prefer UVA's risk-reward balance—it delivers 80% of UVB's benefits with far less potential for leaf burn or operator exposure concerns.
How much UV/IR supplementation do I need for a 4x4 tent?
A 4x4 tent typically runs 400-600W of primary LED lighting, so target 20-50W of combined UV and IR supplementation (5-10% of primary output). The Spider Farmer UV60 & IR30 Bar Set is sized perfectly for this application, providing adequate coverage without overwhelming your canopy. Position bars perpendicular to your main light fixture at 12-18 inches above canopy level for even distribution across all plant zones.
When should I turn on UV supplementation during the flowering cycle?
Introduce UV supplementation during weeks 5-6 of flowering, starting at 50% intensity for 2 hours daily. Gradually increase to 3-4 hours at full power by week 7, maintaining this protocol through the final harvest week. Early flowering phases prioritize bud structure development over secondary metabolites, so premature UV exposure wastes energy without measurable resin benefits. The final 3-4 weeks represent peak cannabinoid and terpene synthesis—this is when UV stress responses deliver maximum returns.
Can I run UV and IR bars at the same time as my main LED?
Yes—far-red infrared should run continuously with your primary light cycle to maintain the Emerson Effect, while UVA operates on a restricted schedule (2-4 hours during mid-cycle). Many cultivators use separate timers or integrate both into environmental controllers for automated scheduling. Combined UV + FR bars like the Medic Grow model simplify installation but require controller integration to independently manage each spectrum's timing for optimal results.
Do UV bars work with any brand of LED grow light?
Supplemental UV and IR bars are brand-agnostic and mount to any fixture with standard hanging hardware or magnetic brackets. Spider Farmer bars include universal mounting clips compatible with their own fixtures plus AC Infinity, Mars Hydro, and most bar-style LEDs. The key compatibility factor is physical clearance—ensure your tent height accommodates both primary lights and supplemental bars with proper spacing (12-18") between fixtures and canopy.
What are the risks of using too much UV supplementation?
Excessive UV exposure causes leaf bleaching, stunted growth, and reduced photosynthetic efficiency—symptoms appear within 48 hours as yellowing or white patches on upper foliage. Start conservative with 2-hour daily exposures and monitor for stress indicators before increasing duration. Commercial operators use light meters to measure UV intensity at canopy level, targeting 15-25 μmol/m²/s of UVA during supplementation windows. This measured approach prevents tissue damage while maximizing beneficial stress responses.
Does far-red infrared really improve yields or just speed up flowering?
Far-red infrared delivers both outcomes through different mechanisms. The Emerson Effect (far-red + red light synergy) boosts photosynthetic efficiency by 20-30%, directly translating to larger yields. Separately, end-of-day far-red exposure accelerates flowering transitions by manipulating phytochrome ratios, effectively shortening total crop time by 5-7 days without sacrificing bud development. Professional growers leverage both effects simultaneously—continuous far-red during light cycles for yield enhancement, plus targeted end-of-day exposure for schedule optimization.
How do I mount UV/IR bars in my grow tent without damaging my main light?
Most supplemental bars include magnetic mounts that attach directly to aluminum heat sinks on bar-style LEDs, or use adjustable hanging clips that hook onto tent poles independently. Position bars perpendicular to your main fixture to fill spectrum gaps across the canopy rather than stacking them parallel, which creates hotspots. For quantum board-style primary lights without exposed metal surfaces, use independent ratchet hangers to suspend UV/IR bars at the same height as your main fixture, maintaining 12-18" clearance from plant tops.
