Light is the engine that powers your terrarium. Without adequate light, plants cannot photosynthesise, leading to weak growth and eventual decline. Too much light, particularly direct sun, can overheat enclosed containers and damage delicate foliage. Understanding light requirements is essential for terrarium success.
Why Light Matters
Plants use light energy to convert carbon dioxide and water into glucose through photosynthesis. This process fuels all plant functions—growth, maintaining cellular health, and producing the oxygen that keeps closed terrariums breathable. Without sufficient light, these processes slow or stop entirely.
Beyond basic survival, light quality affects plant appearance. Insufficient light causes etiolation—stretched, pale growth as plants reach desperately toward any available light source. Proper lighting produces compact, healthy growth with vibrant colouration.
Understanding Light Intensity
Light intensity is measured in lux or foot-candles, but most terrarium keepers work with more practical terms: low, medium, bright indirect, and direct light. Understanding these categories helps you match plants to available conditions.
Light Levels Explained
- Low light: Areas far from windows; roughly 50-250 lux
- Medium light: Several metres from windows; 250-1000 lux
- Bright indirect: Near windows but no direct sun; 1000-5000 lux
- Direct light: Unfiltered sunlight hitting plants; 10,000+ lux
Natural Light for Terrariums
Natural light is ideal when available in the right intensity and duration. It provides the full spectrum plants evolved under and costs nothing. However, using natural light requires understanding how it varies by location, season, and time of day.
Window Orientation in Australia
In the Southern Hemisphere, window orientation affects light differently than described in Northern Hemisphere guides. North-facing windows receive the most direct light throughout the day—often too intense for closed terrariums. South-facing windows provide gentler, more consistent indirect light. East-facing windows offer morning sun, while west-facing windows deliver harsh afternoon sun.
For most terrariums, south or east-facing windows provide excellent conditions. North-facing windows may require the terrarium to be set back or filtered with sheer curtains. West-facing windows are generally too intense, especially in summer.
The Danger of Direct Sun
Direct sunlight through glass creates a greenhouse effect that rapidly elevates temperatures inside enclosed containers. A closed terrarium in direct sun can reach 40°C or higher within minutes—cooking plants and disrupting the ecosystem. Even open terrariums with succulents can overheat if direct sun exposure is prolonged.
Position terrariums where they receive bright ambient light without direct sun rays hitting the container. If this isn't possible, use sheer curtains to filter incoming light or relocate the terrarium to a more suitable spot.
Simple Test
Hold your hand where your terrarium sits at noon. If you can feel warmth from the sun on your skin, that spot receives too much direct light for closed terrariums.
Seasonal Light Changes
Australian seasons bring significant light variations. Summer days are long with intense sun angles that may reach spots in shadow during winter. Winter days are shorter with lower-angle light that may not penetrate as deeply into rooms.
Reassess your terrarium's position seasonally. A perfect winter spot might receive dangerous direct sun in December. Conversely, a location that was bright in summer might become too dim in June. Be prepared to relocate your terrarium as conditions change.
Artificial Lighting Options
When natural light is insufficient or inconsistent, artificial lighting provides a reliable alternative. Modern grow lights offer efficiency and effectiveness that makes them practical for home use.
LED Grow Lights
LED technology has revolutionised plant lighting. Modern LED grow lights consume little electricity, generate minimal heat, and provide precisely the light spectrum plants need. They're available as bulbs that fit standard fixtures, clip-on lights for small spaces, or panel lights for larger setups.
When selecting LED grow lights, look for "full spectrum" options that include both blue and red wavelengths. Blue light promotes compact, leafy growth, while red light supports flowering and overall plant health. Balanced full-spectrum LEDs appear white or slightly pink to human eyes.
Fluorescent Lights
Compact fluorescent lights (CFLs) and fluorescent tubes can also support terrarium plants. They're less energy-efficient than LEDs but often cheaper initially. Standard cool white fluorescent bulbs provide acceptable light for many terrarium plants, though dedicated "daylight" or grow-specific fluorescents perform better.
Placement and Duration
Position artificial lights 15-30 centimetres above your terrarium for most plant types. Too close and you risk heat damage (even with LEDs, which do produce some heat); too far and light intensity drops significantly. Adjust based on your specific light's power and your plants' responses.
Run artificial lights for 10-14 hours daily to simulate natural day length. Use a timer to maintain consistency—irregular lighting stresses plants. Avoid 24-hour lighting, as plants need dark periods for certain metabolic processes.
LED Selection Tips
- Look for lights rated 2000-3000 lumens for small terrariums
- Choose full-spectrum options over red/blue only
- Consider lights with adjustable brightness for fine-tuning
- Check heat output—touch the light after an hour to assess
Matching Light to Plant Needs
Different terrarium plants have different light requirements. Matching your available light to appropriate plants—or providing artificial light to meet plant needs—is essential for success.
Low-Light Tolerant Plants
Mosses, many ferns, and fittonia tolerate lower light levels well. These plants evolved on forest floors where tree canopy filtered most direct sun. They're excellent choices for terrariums in less-bright locations or for those relying on modest artificial lighting.
Medium-Light Plants
Most common terrarium plants—peperomias, nerve plants, and small tropical foliage—thrive in medium light. They need more than deep shade but not bright direct exposure. Bright indirect natural light or properly positioned grow lights satisfy these needs.
High-Light Plants
Succulents and cacti evolved in environments with intense sunlight. They require bright conditions—often brighter than typical indoor settings provide. For succulent terrariums, choose the brightest indirect location available, or supplement with strong artificial lighting.
Signs of Light Problems
Insufficient Light
- Pale, washed-out leaf colour
- Stretched, leggy growth between leaves
- Plants leaning strongly toward light sources
- Slow or no new growth
- Lower leaves yellowing and dropping
Excessive Light
- Bleached or white patches on leaves
- Brown, crispy leaf edges or tips
- Faded or washed-out colours (especially in colourful plants)
- Soil drying out unusually quickly
- Wilting despite adequate moisture
Creating Light Gradients
In larger terrariums, you can create light gradients that accommodate plants with different needs. Position the terrarium where one side receives more light than the other. Place higher-light plants toward the brighter side and shade-lovers in the dimmer areas. This natural variation mimics forest environments where light penetration varies.
Combining Natural and Artificial Light
Many terrarium keepers use a hybrid approach: natural light when available, supplemented by artificial lighting during dark periods or overcast days. This strategy ensures consistent light availability while taking advantage of free natural illumination.
If using both sources, ensure total light duration doesn't become excessive. Plants still need darkness. Time artificial lights to supplement, not extend indefinitely beyond natural day length.
Long-Term Light Management
Over time, observe how your terrarium responds to its lighting conditions. Healthy growth, vibrant colours, and stable moisture cycles indicate proper light levels. Adjust positioning or artificial lighting based on actual plant responses rather than theoretical ideals. Every space is unique, and what works for one terrarium keeper may need modification in your specific situation.
For more on terrarium care, explore our complete maintenance guide or learn about seasonal care for Australian conditions.