Veg vs. Flower: Adjusting LEDs for Every Cannabis Phase

Getting Your Light Right From Seed to Harvest

If you’re growing cannabis indoors, understanding how to adjust your lighting for each stage of growth isn’t just helpful—it’s essential. Lighting is the lifeblood of any grow room. And with indoor LED grow lights, you have more control than ever before. But here’s the catch: different stages of cannabis growth demand different light intensities and spectrums.

If you're using the same setup from veg to flower without tweaking anything, you’re not doing your plants any favors.

Let’s walk through how to fine-tune your indoor LED grow lights for both the veg and flowering phases to help your plants thrive.

Vegetative Stage: Laying the Foundation

What’s happening here?

During the veg stage, your cannabis plants are growing leaves, stems, and roots. They’re laying the groundwork for big buds later on.

Light Needs

At this point, your plants need more blue spectrum light. Why? Because blue light promotes compact, bushy growth—exactly what you want before flowering. This is where indoor LED grow lights shine, especially those with full-spectrum or adjustable settings.

Ideal Setup for Vegging:

• Spectrum: 60–70% blue, 30–40% red

• PPFD (light intensity): 300–500 µmol/m²/s

• Light duration: 18–24 hours per day

Tips:

• Keep lights at the right height to prevent stretching.

• Use a timer to maintain consistent light cycles.

• Adjust based on plant response—some strains love it bright, others need moderation.

Flowering Stage: Shifting Gears

What changes?

Now, your plant wants to reproduce. That means it’s time to form flowers (aka buds). To do this efficiently, your lighting setup needs to change.

Light Needs

Red light takes the lead here. It encourages bud production and triggers hormones that signal the plant to bloom. Full-spectrum indoor LED grow lights often allow you to emphasize red and far-red wavelengths during this phase.

Ideal Setup for Flowering:

• Spectrum: 60–70% red, 30–40% blue

• PPFD: 600–1000 µmol/m²/s

• Light duration: 12 hours on, 12 hours off

Tips:

• Make the switch to 12/12 light gradually to reduce plant stress.

• Monitor heat levels—even efficient indoor LED grow lights can build warmth.

• Keep an eye out for signs of light burn (bleached tops or curled leaves).

Transition Tips: Veg to Flower

The switch from veg to flower is critical. A sudden change in light spectrum or intensity can shock your plants.

Instead:

• Ease into new settings by lowering the blue and increasing the red spectrum over a few days.

• Trim your plants just before switching lights to reduce stress.

• Maintain airflow and humidity, especially as the lights get more intense.

Common Mistakes to Avoid

• Using the same spectrum throughout the growth: Plants need different light “recipes” at different times.

• Mounting LEDs too close or too far: Incorrect positioning can lead to stretching or light burn.

• Not adjusting intensity: Seedlings don’t need the same strength as flowering colas.

Remember, indoor LED grow lights give you flexibility, but only if you take advantage of it.

FAQs

Q1: Can I use the same LED grow light for both veg and flower stages?Yes, as long as it's a full-spectrum LED or one with adjustable settings. The key is to change the spectrum and intensity as your plant matures.

Q2: How close should indoor LED grow lights be during flowering?It depends on the model, but generally 12–18 inches above the canopy works. Always monitor your plants for signs of light stress.

Q3: What happens if I don’t change the light schedule when switching to flowers?Your plant might stay in veg mode. Cannabis relies on light cycles to know when to flower, so a 12/12 light schedule is essential for triggering bloom.