Planted Tank Lighting Guide: Understanding PAR Values and Photoperiods

Lighting is the most critical factor for successful planted aquariums, yet it’s also one of the most misunderstood aspects of aquascaping. The difference between a thriving underwater garden and an algae-filled disaster often comes down to lighting choices. This comprehensive guide explores everything from basic photoperiods to advanced PAR measurements, helping you create the perfect lighting environment for your aquatic plants.

The Science of Aquarium Lighting

How Plants Use Light

Aquatic plants convert light energy into chemical energy through photosynthesis. Understanding this process helps explain why lighting specifications matter:

The Photosynthesis Equation:

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ (glucose) + 6O₂

Key Light Requirements:

Intensity: How much light energy is available
Spectrum: The wavelengths (colors) of light
Duration: How long light is provided (photoperiod)
Consistency: Stable daily patterns

Photosynthetically Active Radiation (PAR)

PAR measures the light wavelengths plants can actually use for photosynthesis (400-700 nanometers). This is the most accurate way to evaluate aquarium lighting.

Understanding PAR Measurements:

PAR Level	Classification	Best For	Effects
15-30 μmol/m²/s	Low light	Low-tech tanks, mosses, ferns, Anubias	Slow growth, minimal CO₂ required, low algae risk
30-50 μmol/m²/s	Medium light	Most stem plants, Cryptocoryne, moderate growth	Balanced growth, requires some CO₂, manageable algae
50-80 μmol/m²/s	High light	Carpeting plants, red plants, fast growth	Rapid growth, CO₂ essential, algae management critical
80+ μmol/m²/s	Very high light	Professional aquascapes, competition tanks	Expert-level maintenance, precise balance required

How to Measure PAR:

PAR meters: Apogee MQ-510, Seneye, or similar ($200-400)
Smartphone apps: Less accurate but useful for relative measurements
DIY methods: Limited accuracy but better than guessing
Manufacturer data: Some companies provide PAR charts for their lights

Measuring PAR in Your Tank:

Take readings at multiple depths and positions:

Surface (just below water)
Mid-depth (middle of tank)
Substrate level (bottom of tank)
Multiple locations across tank surface

Create a PAR map to understand light distribution.

Light Spectrum and Plant Growth

Different wavelengths affect plants differently:

Blue Light (400-500nm):

Drives photosynthesis efficiently
Promotes compact growth
Encourages leaf development
Essential for stem elongation control
Often appears dim to human eyes

Red Light (600-700nm):

Maximum photosynthesis efficiency
Promotes flowering and fruiting (less relevant for aquatics)
Stimulates pigmentation in red plants
Can encourage algae if unbalanced

Green Light (500-600nm):

Reflected by plants (why they appear green)
Less efficient for photosynthesis
Important for visual appeal
Penetrates water well

Full Spectrum Requirements:

Plants need balanced light across the spectrum:

4000-5000K: Warm white, good all-purpose spectrum
6500K: Daylight balanced, excellent for plants and viewing
10000K: Cool white, penetrates deep water well
RGB: Programmable color mixing (aesthetic focused)

Light Penetration in Water

Water absorbs and scatters light:

Depth vs. Light Intensity:

Depth	Light Remaining	PAR Impact
Surface	100%	Baseline measurement
12 inches (30cm)	70-80%	20-30% reduction
18 inches (45cm)	50-65%	35-50% reduction
24 inches (60cm)	35-50%	50-65% reduction

Factors Affecting Penetration:

Water clarity (tannins reduce light)
Surface agitation (reduces reflection)
Suspended particles (cloudy water blocks light)
Glass thickness (minimal impact with modern tanks)
Light fixture height above water

Lighting Technologies Compared

LED Lighting (Current Gold Standard)

LED technology dominates the aquarium lighting market in 2025-2026, and for good reason.

Advantages:

Energy efficiency (50-70% less power than alternatives)
Long lifespan (30,000-50,000 hours)
Programmable spectrum and intensity
Minimal heat output
Slim profile and modern aesthetics
Adjustable mounting systems
Dimming capabilities
Built-in timers (many models)

Disadvantages:

Higher upfront cost (though prices dropping)
Spectrum quality varies by manufacturer
Some cheaper units have reliability issues
PAR output varies significantly between models

Top LED Brands (2025-2026):

Brand	Series	Price Range	Best For	Key Features
Chihiros	WRGB II, A II	$80-200	All planted tanks	High PAR, app control, RGB
Twinstar	S, E, C series	$100-250	Mid-high light	Excellent spread, minimal shadow
Fluval	Plant 3.0	$150-300	Premium setups	Bluetooth control, sunrise/sunset
Finnex	Planted+, Ray2	$70-150	Budget-conscious	Good PAR, simple operation
ONF	Flat Nano	$80-180	Small tanks	Beautiful design, good spread
Nicrew	Classic LED Plus	$30-70	Beginners	Affordable, decent PAR
Week Aqua	M series	$120-220	High-tech tanks	High PAR output, good value
Current USA	Satellite Freshwater Pro	$100-200	Features-focused	Ramp timer, weather effects

Budget Picks ($30-75):

Nicrew Classic LED Plus
Hygger Auto On/Off
Beamworks LED
Aqueon LED

Mid-Range Picks ($75-150):

Finnex Planted+ 24/7
Chihiros A II series
Twinstar E series

Premium Picks ($150+):

Chihiros WRGB II
Twinstar S series
Fluval Plant 3.0
ONF Flat One+

T5/T8 Fluorescent Lighting

Once the standard for planted tanks, now largely replaced by LEDs but still relevant.

Advantages:

Excellent light spread (minimal shadowing)
Proven plant growth results
Good spectrum options available
Lower upfront cost than premium LEDs
Easy bulb replacement

Disadvantages:

Higher power consumption
Bulbs need replacement every 12-18 months
Generate significant heat
Bulky fixtures
Limited dimming/programming

Best Applications:

Large tanks (6+ feet) where spread matters
Commercial setups
Supplemental lighting for high-tech tanks
Breeders with many tanks (cost-effective)

Recommended Bulbs:

GE Plant and Aquarium: 6500K, budget option
Philips T5 HO: Good spectrum, reliable
Aquatic Life T5 HO: Aquarium-specific
ATI T5: Premium option, excellent spectrum

Metal Halide (HID) Lighting

High-intensity discharge lighting, primarily for deep tanks and SPS coral.

Advantages:

Maximum light penetration
Excellent for very deep tanks (24+ inches)
Intense point-source lighting
Proven for demanding corals

Disadvantages:

Extremely hot (requires cooling)
High power consumption
Bulky fixtures and ballasts
Bulb replacement every 8-12 months
Overkill for most planted tanks
Expensive

Current Status:

Mostly obsolete for planted freshwater tanks in 2025-2026. LEDs provide sufficient intensity for even deep tanks without the heat and energy costs.

Compact Fluorescent (CFL)

Older technology, largely obsolete for aquariums.

Only viable for:

Very small nano tanks (5 gallons or less)
Temporary/emergency lighting
DIY projects on extreme budgets

Not recommended for serious planted tanks.

Calculating Your Lighting Needs

The WPG (Watts Per Gallon) Fallacy

Old rule: 2-3 watts per gallon for medium light.

Why WPG Doesn’t Work:

LED efficiency varies dramatically (some 1W LEDs outperform 3W LEDs)
Tank depth matters more than volume
Spread and distribution aren’t accounted for
Reflectors and optics affect output
Plant requirements vary by species

Better Approach: PAR-Based Planning

Determining Required PAR

Step 1: Identify Your Goal

Tank Type	Target PAR at Substrate	Examples
Low-tech/no CO₂	20-30 μmol/m²/s	Moss tanks, Java fern, Anubias
Medium-tech	30-50 μmol/m²/s	Cryptocoryne, most stem plants, Vallisneria
High-tech/CO₂	50-80 μmol/m²/s	Carpeting plants, red plants, advanced aquascapes
Professional	80+ μmol/m²/s	Competition aquascapes, demanding species

Step 2: Consider Tank Depth

Deeper tanks require higher surface PAR to achieve target substrate PAR:

Tank Depth	Required Surface PAR for 40 PAR at Substrate
12 inches	50-55 PAR
16 inches	65-75 PAR
20 inches	85-100 PAR
24 inches	110-130 PAR

Step 3: Account for Plant Species

Plant Category	PAR Requirement	Examples
Low light	15-25 PAR	Java moss, Anubias, Java fern, Cryptocoryne wendtii
Medium light	25-45 PAR	Cryptocoryne, Vallisneria, Amazon sword, most stem plants
High light	45-70 PAR	Monte Carlo, dwarf hairgrass, Rotala, Ludwigia
Very high light	70+ PAR	HC Cuba, tonina, Bucephalandra red varieties, red aquatic moss

Lighting Calculator Formula

Simplified Approach:

Determine desired substrate PAR
Estimate PAR drop based on tank depth (approximately 40-50% loss per 12 inches)
Select light fixture with sufficient output at surface
Consider spread and uniformity

Example Calculation:

20-gallon long tank (12 inches deep)
Target: 40 PAR at substrate
Estimated light drop: 35% over 12 inches
Required surface PAR: 40 ÷ 0.65 = ~62 PAR
Select light providing 60-70 PAR at surface

Photoperiod Management

Understanding Photoperiod

Photoperiod refers to the duration of light exposure in a 24-hour cycle. Just as important as intensity, photoperiod dramatically affects plant health and algae growth.

Natural Light Cycles:

Tropical regions: 10-12 hours of daylight year-round
Temperate regions: 8-16 hours (seasonal variation)
Aquarium standard: 6-10 hours (shorter prevents algae)

Recommended Photoperiods by Tank Type

Tank Type	Photoperiod	Notes
New tank (first month)	5-6 hours	Prevents algae while establishing
Low-tech tanks	6-7 hours	Balance growth without CO₂
Medium-tech tanks	7-8 hours	Standard for CO₂-injected tanks
High-tech tanks	8-10 hours	Requires precise CO₂ and nutrient balance
Algae-prone tanks	Reduce to 6 hours	Temporary reduction to combat algae
Highlight tanks	7-8 hours	More light intensity, less duration

The Ramp Up/Ramp Down Approach

Sudden on/off lighting stresses plants and fish.

Recommended Schedule:

Time	Light Level	Duration
Dawn simulation	10-20% intensity	30-60 minutes
Sunrise	50% intensity	30 minutes
Full intensity	100%	Main photoperiod (6-8 hours)
Sunset	50% intensity	30 minutes
Dusk	10-20%	30 minutes
Off	0%	Night

Benefits:

Mimics natural conditions
Reduces fish stress
Prevents algae by avoiding sudden light changes
Allows plants to adjust photosynthesis gradually

Implementation:

Many LED fixtures have built-in ramp timers
Smart plugs with dimmable LEDs
Manual dimming (less convenient but effective)

The Noon Burst Technique

For demanding plants without full-day high light:

Base lighting: 30-40 PAR for 8-10 hours
Midday burst: 60-80 PAR for 3-4 hours at tank’s peak time

Benefits:

Reduces overall energy costs
Lower algae risk than all-day high light
Sufficient for most demanding plants
Mimics natural midday sun intensity

Algae Control Through Lighting

Understanding the Light-Algae Relationship

Algae thrive on:

Excessive light intensity
Extended photoperiods
Light spectrum imbalances
Inconsistent timing
Sudden light changes

Algae Types and Light Triggers

Algae Type	Light Trigger	Prevention
Green spot algae	Too much light, long photoperiod	Reduce intensity, shorten photoperiod
Green water (algae bloom)	Excessive light + nutrients	Blackout for 3-5 days, then reduce light
Hair/thread algae	High light + CO₂ imbalance	Reduce light, balance CO₂
Brown diatoms	Low light + silicates	Increase light, ensure proper spectrum
Black beard algae	Fluctuating CO₂ + high light	Stabilize CO₂, reduce light intensity
Staghorn algae	Poor circulation + high light	Improve flow, reduce light

The Algae Control Protocol

When Algae Appears:

Step 1: Immediate Actions

Reduce photoperiod to 6 hours
Reduce intensity by 25%
Perform water change (50%)
Clean algae manually

Step 2: Monitor for 1 Week

Continue reduced lighting
Maintain water changes (30% every 3 days)
Check CO₂ levels (if applicable)
Test nutrients (nitrate, phosphate)

Step 3: Gradual Restoration

If algae under control:
- Increase duration by 30 minutes weekly
- Restore intensity slowly
- Monitor constantly

Step 4: Blackout (Severe Cases)

Complete darkness for 3-5 days
No peeking (even brief light exposure helps algae)
Continue filtration and CO₂
Fish will be fine
Usually eliminates severe algae outbreaks

Balancing Light with CO₂ and Nutrients

The “golden triangle” of planted tank success:

High Light + Low CO₂ + Limited Nutrients = Algae City

Balanced Approach:

Light Level	CO₂ Required	Nutrient Level
Low (20-30 PAR)	Optional	Low to moderate
Medium (30-50 PAR)	Beneficial	Moderate
High (50-80 PAR)	Essential	High
Very High (80+ PAR)	Essential + precise	High + precise

The Formula:

Increase light only when you can provide:

Adequate CO₂ (20-30 ppm for high light)
Sufficient nutrients (NPK + micronutrients)
Consistent maintenance routine
Time for algae management

Advanced Lighting Strategies

Color Temperature Manipulation

Adjusting spectrum for specific effects:

Enhancing Red Plants:

Increase red spectrum output
Reduce blue slightly
Boost white overall
Commercial “red plant” settings available on some fixtures

Growth vs. Viewing:

Growth mode: Higher blue, higher intensity, cooler white
Viewing mode: Warmer white, reduced blue, aesthetic RGB
Many fixtures offer programmable modes

Dawn/Dusk Colors:

Warm orange/red for sunrise/sunset simulation
Cool blue for “moonlight” periods
Pure white during peak hours

Multiple Light Fixtures

Using several fixtures for complex setups:

Front-to-Back Lighting:

Front fixture: Medium intensity for foreground
Rear fixture: Higher intensity for stem plants
Allows zonal control

Color Separation:

One fixture: Warm white (growth)
One fixture: Cool white + RGB (viewing)
Run separately for different effects

Supplemental Lighting:

Main fixture: General coverage
Spotlights: Specific plants needing extra light
Useful for highlighting red plants or carpets

Seasonal Simulation

Some advanced hobbyists simulate seasonal changes:

Summer Mode:

10-12 hour photoperiod
Higher intensity
Warm white spectrum
Triggers growth and reproduction

Winter Mode:

6-8 hour photoperiod
Lower intensity
Cooler white spectrum
Simulates rest period

Benefits:

Mimics natural conditions
May trigger breeding in some species
Prevents algae through variation
Interesting aesthetic changes

Lighting by Tank Size and Type

Nano Tanks (5-15 gallons)

Challenges:

Limited space for fixtures
Shallow depth (light intensity issues)
Often open-top (spatter concerns)

Solutions:

Under 10 gallons:

Clip-on LED (ONF Flat Nano, Chihiros C2)
Desk lamp with 6500K LED bulb
NICREW clip light
PAR target: 30-50 at substrate

10-15 gallons:

Chihiros A II or C2 series
Twinstar Nano
Finnex Stingray
PAR target: 30-60 at substrate

Standard Tanks (20-55 gallons)

20-gallon long (30” × 12” × 12”):

Single Chihiros A II or Finnex Planted+
PAR target: 40-60
Good for carpeting plants

29-30 gallons:

Chihiros WRGB II 60cm
Fluval Plant 3.0 36”
PAR target: 40-70

40-55 gallons:

Twinstar S-series (60-90cm)
Chihiros WRGB II 90cm
Two Finnex Planted+ (for 4-foot tanks)
PAR target: 40-80

Large Tanks (75+ gallons)

75-gallon (48” × 18” × 21”):

Two Chihiros WRGB II 60cm (side by side)
One Twinstar 120cm
Four T5 HO bulbs (for even spread)
PAR target: 50-80

125-gallon (72” × 18” × 21”):

Three LED fixtures or six T5 bulbs
Consider hanging pendant lights
PAR target: 50-80

Deep Tanks (24+ inches):

Multiple fixtures or pendant lights
Higher surface PAR required
Consider Kessil or similar high-penetration LEDs
PAR target: 40-60 at substrate (will require 100+ PAR at surface)

Lighting Maintenance and Troubleshooting

Fixture Maintenance

Monthly:

Clean fixture housing and lens
Check for moisture intrusion
Inspect mounting hardware
Verify timer settings

Quarterly:

Deep clean (unplug first!)
Check for LED degradation (if dimming)
Update programming if needed
Test PAR levels (if meter available)

Annually:

Evaluate if upgrades needed
Replace cheap fixtures if failing
Reassess lighting needs as plants mature

Troubleshooting Common Problems

Problem: Plants Not Growing

Possible causes:

Insufficient PAR (measure at substrate)
Wrong spectrum (ensure 6500K or full spectrum)
Photoperiod too short (increase to 8 hours)
Insufficient CO₂ or nutrients
Wrong plants for light level

Problem: Excessive Algae

Solutions:

Reduce photoperiod by 1-2 hours
Lower intensity by 20%
Ensure CO₂ and nutrients are balanced
Check for light leaks (room light, sunlight)
Blackout for 3 days if severe

Problem: Uneven Growth

Solutions:

Add second fixture for better spread
Raise fixture height for more even distribution
Trim overgrown plants blocking light
Consider spotlighting for specific areas
Use risers or hanging kit for better positioning

Problem: Fish Stress

Solutions:

Implement ramp timer (gradual on/off)
Add dim period at noon (siesta)
Ensure hiding places for shy fish
Reduce intensity if fish hide constantly
Check if light too bright for species

Budget Lighting Solutions

DIY LED Options

LED Strip Lights:

5050 or 5630 LED strips (6500K)
Mount in aluminum channel for heat dissipation
Use 12V or 24V power supply
Cost: $20-40 for small tank
Good for: Low to medium light setups

Cree LED Bulbs:

6500K Cree CXB or similar
DIY pendant lights
Excellent PAR per watt
Cost: $30-60 per fixture
Good for: Medium to high light

Refurbished Shop Lights:

4-foot LED shop lights (5000-6500K)
Hang over tank
Surprisingly effective for larger tanks
Cost: $30-50
Good for: Low-tech 40+ gallon tanks

Getting the Most from Budget Fixtures

Improving Cheap LEDs:

Add reflectors (aluminum foil, Mylar)
Lower fixture closer to water (increases PAR)
Use multiple small fixtures instead of one large
Combine with natural window light (carefully)
Upgrade bulbs if fixture allows

Conclusion

Lighting is both an art and a science in planted aquariums. The perfect lighting setup balances plant health, visual appeal, algae control, and fish comfort. By understanding PAR values, spectrum effects, and photoperiod management, you can create an aquatic environment where plants thrive and fish display their best colors.

Remember that lighting doesn’t exist in isolation—it must be balanced with CO₂, nutrients, water quality, and maintenance routines. Start conservative with both intensity and duration, then adjust based on observation. Plants will tell you if they need more light through leggy growth and pale colors; algae will tell you if you have too much.

The investment in quality lighting pays dividends through lush plant growth, reduced algae problems, and stunning visual displays. Whether you’re running a simple low-tech tank or a competition-level aquascape, proper lighting is the foundation upon which all other success is built.

Take time to research fixtures, measure PAR if possible, and start with conservative photoperiods. Your patience will be rewarded with a thriving underwater garden that becomes the centerpiece of your space.

Lighting Setup Checklist:

Quick Reference: PAR Targets by Plant Type

Anubias, Java fern, mosses: 15-25 PAR
Cryptocoryne, Vallisneria: 25-40 PAR
Stem plants, Amazon sword: 40-60 PAR
Carpeting plants, red plants: 60-80 PAR
HC Cuba, demanding species: 80+ PAR