Grow Lights Distance Chart UK | LED, Fluorescent & HPS Guide

---

Getting the distance right between your plants and their grow lights is one of the most important factors in successful indoor growing. Hang a light too close and leaves can bleach or curl from excess intensity; hang it too far away and plants stretch, weaken and produce poor yields. The correct grow light distance depends on your light type, LED wattage, PPFD output and plant growth stage.

This guide includes a clear grow lights distance chart for UK growers, with recommended heights for seedlings, vegetative plants and flowering crops. You’ll also find wattage-specific LED distances, troubleshooting signs, and practical tips for adjusting height as your plants grow.

For a broader overview of grow light types, setup, and indoor use, see our Grow Lights UK complete guide, which also links out to more detailed deep-dive articles on topics like light spectrum, distance, and timing.

---

Why Grow Lights Distance Matters

Grow lights provide the intensity and spectrum that plants often can’t get from natural UK daylight — especially through autumn and winter. But even the best LED will underperform if it’s hung at the wrong height.

Too close:

• leaves bleach, curl or scorch
• PPFD becomes excessive
• seedlings stall or die back

Too far:

• plants stretch tall and weak
• internodes lengthen
• fruiting plants may fail to flower or ripen

Setting the correct distance ensures:

• compact, sturdy seedlings
• healthy vegetative growth
• reliable flowering and fruiting
• even canopy development across your setup

Grow lights are especially valuable for:

• winter herbs and salad greens
• starting tomatoes, peppers and chillies early
• improving propagation and rooting success
• growing vegetables in low-light kitchens or lofts

If you’re setting up indoor lighting for the first time, our How to Set Up Grow Lights guide covers reflective surfaces, positioning, airflow and dimming — all factors that affect how close your lights should hang.

Once you understand how distance influences PPFD and plant behaviour, adjusting your lights becomes simple and intuitive

---

General Grow Lights Distance Guidelines

Grow light distance depends on your lamp type, wattage, and the amount of PPFD your plants need. These are reliable starting points for most UK indoor growers:

---

LED Grow Lights (most modern panels)

12–24 inches (30–60 cm)
Use the lower end for flowering and higher-output bar LEDs, and the upper end for seedlings or very bright quantum boards.

• Bar-style LEDs can sit slightly closer due to better heat distribution.
• Dim high-output LEDs before lowering them.

---

Fluorescent Grow Lights (T5 or CFL)

2–6 inches (5–15 cm)
These run cool and produce gentle light, so they can sit close to the canopy — ideal for seedlings, microgreens and propagation.

---

HPS Grow Lights

24–36 inches (60–90 cm)
HPS lights run hot and should always be kept further from plants. Use good extraction and airflow to avoid heat stress.

⚠️ Household bulbs are not suitable — they don’t produce the right spectrum or strength for plant growth.

---

Grow Lights Distance by Plant Stage

---

Different growth stages require different intensities, so the ideal hanging height changes as your plants develop. These distance ranges are suitable for most mid-range LED grow lights (200–400 W), with notes for fluorescent and HPS alternatives.

A full hanging-height reference for bulbs, bars and LED panels is also available in our How to Set Up Grow Lights guide.

---

🌱 Seedlings (Low PPFD: 200–300 µmol/m²/s)

Seedlings are sensitive and easily scorched, so lights should sit higher.

• LED: 24–30 in (60–75 cm)
  Raise higher for strong bar LEDs or high-efficiency (2.7–3.0 µmol/J) boards.
• Fluorescent (T5/CFL): 2–4 in (5–10 cm)
• HPS: Not recommended due to excessive heat and intensity.

Seedlings should remain compact and upright. If they stretch, lower the light slightly.

---

🌿 Vegetative Growth (Medium PPFD: 400–600 µmol/m²/s)

Plants develop leaves and structure in this phase, so they can tolerate stronger light.

• LED: 18–24 in (45–60 cm)
  Bar LEDs often work best at the lower end of this range.
• Fluorescent: 4–6 in (10–15 cm)
• HPS: 24–36 in (60–90 cm) depending on heat and ventilation.

If leaves darken or angle upward (“praying”), your PPFD is near optimal.

---

🌼 Flowering & Fruiting (High PPFD: 700–1000+ µmol/m²/s)

Plants now benefit from strong intensity to support bud, fruit or flower formation.

• LED: 12–18 in (30–45 cm)
  Lower only if running dimmed; intense LEDs too close can cause bleaching.
• Fluorescent: ≈6 in (15 cm)
• HPS: 18–24 in (45–60 cm)

If tips bleach or upper leaves taco upward, raise the light slightly.

---

LED Grow Lights Distance by Wattage

LED distance isn’t only about wattage — it also depends on the fixture’s efficiency, spectrum and lens design. But wattage gives a useful starting point, especially when choosing between different LED panels.

If you’re unsure how powerful your light actually is, our Grow Light Wattage Explained guide breaks down real power draw, LED efficiency, and what wattage means in practice.

Below are recommended distances for typical full-spectrum LEDs:

---

💡 100–150 W LED Grow Lights (small tents, herbs & seedlings)

Suitable for seedlings, salad greens, herbs and propagation setups.

• Seedlings: 24–30 in (60–75 cm)
• Vegetative: 18–24 in (45–60 cm)
• Flowering: 12–18 in (30–45 cm)

These LEDs are ideal for beginners and small indoor gardens — see our Best Indoor Grow Lights for Beginners guide for simple plug-and-grow options.

---

💡 300–450 W LED Grow Lights (medium setups, 2×3 ft or 3×3 ft tents)

Good for veg and light flowering.

• Seedlings: 30 in (75 cm)
• Vegetative: 20–24 in (50–60 cm)
• Flowering: 14–18 in (35–45 cm)

Higher-efficiency panels may require slightly more distance or dimming.

---

💡 600–1000 W LED Grow Lights (full-cycle 4×4 ft, 5×5 ft setups)

These produce intense PPFD suitable for demanding crops.

• Seedlings: 36 in (90 cm)
• Vegetative: 24 in (60 cm)
• Flowering: 18–20 in (45–50 cm)

For real-world PPFD maps and manufacturer data, our Top 10 LED Grow Lights UK comparison includes measured outputs for common full-cycle LEDs.

---

⚠️ Important Notes

• Different LEDs with the same wattage can vary drastically in intensity.
• Bar-style LEDs often hang closer than older quantum boards due to better heat distribution.
• Always start higher and lower gradually as plants adapt.

---

Grow Lights Distance Chart

These distances provide a reliable starting point for most indoor gardens. Always adjust based on plant response, light intensity, and dimming level. For beginners, the distances below match typical full-spectrum LEDs used in UK grow tents.

Tip: Bar-style LEDs can usually be hung 2–4 inches (5–10 cm) closer than older quantum-board designs because they spread heat and light more evenly.

Plant Stage	LED Grow Lights	Fluorescent (T5/CFL)	HPS Lights
Seedlings Low PPFD: 200–300 µmol/m²/s	24–30 in (60–75 cm)	2–4 in (5–10 cm)	Not recommended
Vegetative Growth Medium PPFD: 400–600 µmol/m²/s	18–24 in (45–60 cm)	4–6 in (10–15 cm)	24–36 in (60–90 cm)
Flowering & Fruiting High PPFD: 700–1000+ µmol/m²/s	12–18 in (30–45 cm)	≈6 in (15 cm)	18–24 in (45–60 cm)

---

Light Spectrum and Grow Lights

Distance is only part of what determines how plants respond to artificial light. The spectrum your grow light produces influences growth shape, leaf development and flowering.

Here’s how different wavelengths affect your plants:

🔵 Blue Light (400–500 nm)

• Promotes compact, leafy growth
• Ideal for seedlings and vegetative plants
• Helps prevent stretching when lights need to hang slightly higher

🔴 Red Light (600–700 nm)

• Encourages flowering and fruiting
• Drives energy-intensive processes like bud and fruit formation
• Works best at higher PPFD levels (usually 700–1000+ µmol/m²/s)

🌞 Full-Spectrum LEDs

Most modern LED grow lights blend blue, red and white diodes to create a balanced spectrum that mimics natural sunlight. This makes them suitable for all growth stages and more forgiving when adjusting hanging distance.

Because spectrum influences how plants absorb and use light, you may find:

• Plants under blue-heavy spectrums tolerate slightly closer distances
• Plants under red-heavy or high-intensity spectrums often need a bit more space
• Full-spectrum LEDs usually match the distance ranges shown in our chart

Understanding spectrum makes it much easier to adjust distance confidently as your plants move from seedlings → veg → flowering.

For more background on how different wavelengths influence indoor plant growth, you can also refer to the Royal Horticultural Society’s guidance on lighting for houseplants.

---

Troubleshooting Grow Lights Placement

Plants show very clear signs when grow lights are hung too high, too low or producing the wrong intensity. Use the symptoms below to diagnose and correct issues quickly.

---

🔥 Lights Too Close (Excess PPFD / Heat Stress)

Symptoms:

• Pale or bleached leaf tops
• Yellowing between leaf veins (light bleaching)
• Edges curling upward (“tacoing”)
• Crispy or dry leaf tips
• Growth stalls at the top of the canopy

Fix:

• Raise the light 2–4 inches (5–10 cm)
• Dim the fixture slightly if possible
• Increase airflow across the canopy
• Ensure the thermometer/hygrometer is at canopy height

---

🌿 Lights Too Far (Under-lighting / Stretching)

Symptoms:

• Tall, thin, stretched stems
• Large internodal spacing
• Plants leaning toward the light
• Weak, floppy upper growth
• Slow transition into flowering

Fix:

• Lower the light gradually (2–3 inches at a time)
• Increase PPFD if using a dimmer
• Rotate pots weekly for even exposure

---

🌡 Heat Stress (often mistaken for light stress)

Symptoms:

• Leaves curl upward from the edges
• Brown tips despite correct distance
• Canopy temperature exceeds 28–30°C

Fix:

• Improve extraction or intake airflow
• Add an oscillating fan across the canopy
• Raise the light slightly if it runs hot

---

💡 When Distance and Dimming Work Together

Most modern LEDs perform best when you dim during early growth and lower the light, rather than keeping the light high at full power. This provides even coverage and prevents stretching.

Use a PAR/PPFD meter or a reliable phone app to fine-tune intensity — readings within your plant stage targets are more important than matching exact height numbers.

---

Tips for Adjusting Grow Lights Height

Dialling in the correct hanging height is an ongoing process — plants grow, PPFD changes, and tent conditions shift over time. Use these practical tips to keep light intensity in the optimal zone throughout every stage.

---

1. Start Higher, Lower Gradually

New seedlings and young plants are easily stressed. Begin with reduced intensity and a higher hanging height, then lower the light slowly over several days while watching leaf response. This prevents bleaching during early establishment.

---

2. Raise the Light as Plants Grow Taller

As your canopy rises, PPFD naturally increases. Lifting or dimming the light every 1–2 weeks maintains consistent intensity across the canopy and avoids hot spots during rapid vegetative growth.

---

3. Rotate Plants Weekly for Even Growth

Even high-end LEDs can have slight centre–edge differences. Rotating pots once a week ensures uniform light exposure, especially when growing herbs, leafy greens, or compact vegetables.

---

4. Use a PAR or Lux Meter for Accuracy

A handheld PAR meter is ideal, but a calibrated phone app works surprisingly well.
Target PPFD levels:

• Seedlings: 200–400 µmol/m²/s
• Vegetative: 400–700 µmol/m²/s
• Flowering: 800–1,000 µmol/m²/s

Measuring PPFD is more reliable than relying on distance alone.

---

5. Adjust Height When Changing Spectrums or Modes

Some LEDs increase output in “Bloom Mode” or at higher dimmer settings. When switching modes:

• Lower intensity → lower the light
• Higher intensity → raise the light

This avoids sudden jumps in PPFD that stress plants.

---

6. Account for Heat Build-Up in Small Tents

Compact tents (60×60 or 80×80 cm) can heat up quickly. If canopy temperatures exceed 28–30°C, raise the light or improve airflow to keep stress levels down.

---

7. Make One Adjustment at a Time

If plants react badly, you need to know why. Change only height or only dimming — never both together. This makes diagnosing issues far easier.

---

Conclusion

Getting grow-light height right is one of the simplest ways to improve plant health, whether you’re raising delicate seedlings or pushing flowering crops to full productivity. Use the distance ranges and wattage guidelines in this chart as your starting point, then fine-tune based on your plants’ responses — compact growth, strong stems and vibrant leaves indicate you’re in the ideal zone.

Start higher and lower gradually, adjust height as plants grow, and watch for signs of stress. With consistent monitoring, your indoor garden will receive the right intensity at each stage and stay healthy, balanced and productive all year round.

If you want to browse all our grow light guides and comparisons in one place, see our Grow Lights UK hub.

---

📎 Related Guides • Grow Lights UK Our complete guide to grow light types, setup basics, and choosing the right light for your space. • Grow Light Wattage Explained A clear breakdown of real LED wattage, efficiency, and how power output affects PPFD and hanging height. • How to Set Up Grow Lights Indoors Step-by-step guidance on positioning lights, using timers, managing airflow, and adjusting height as plants grow. • Best Indoor Grow Lights UK for Beginners Simple, plug-and-play LED grow lights that are easy to position correctly for herbs, seedlings, and small indoor setups.

---