Light

Light is the most misunderstood, and most important, factor in plant care. Many plant issues blamed on watering, soil, or pests are actually caused by insufficient or inconsistent light. To care for plants successfully long-term, light must be understood not as ambience, but as energy.

light is food

Plants use light to photosynthesize. Without enough light, a plant cannot:

Grow new leaves properly
Maintain leaf size, color, or variegation
Support root health
Use water efficiently

This is why plants can rot in low light even when watered “correctly.”

Light quantity matters more than vague descriptions like “bright” or “low.” Measuring light removes guesswork and leads to predictable results.

understanding light indoors

Indoor light is dramatically weaker than outdoor light, even near windows.

A bright summer day outdoors can exceed 10,000 foot-candles
Most indoor spaces range from 25-300 foot-candles
Plants labeled “low light” still require measurable light to survive

Glass, distance from windows, season, and window direction all significantly reduce usable light.

You may notice that most plant species that are well-known houseplants are tropical. Our indoor environments most closely mimic the temperature and light environments of a tropical rainforest understory, where plants are already more adapted to surviving on less light.

measuring light

The most reliable way to understand light is with a light meter (foot-candles or lux). This allows you to place plants based on actual conditions rather than assumptions.

When measuring:

Measure at leaf height
Measure during the brightest part of the day
Take multiple readings to understand daily variation

Grow lights should also be measured, distance alone is not a reliable indicator of intensity.

Important Note:

You will see us use terms such as foot-candles and lux. Understand that these measurements are only taking snapshots of how much light is present at the instant that you measure it. There are other, more accurate measurements of light, known as PPFD or DLI. While those are better, we feel that they are slightly too complicated for the minimum knowledge you need to give your plants adequate light. If you want to take a deep dive into light, go to this article on houseplantjournal.com, where Darryl, an engineer by trade, can teach you everything about light and help you become a light expert.

Light Categories (indoor reference)

These ranges apply broadly to most common houseplants.

LOW LIGHT

25-75 foot-candles

Survival range for tolerant plants
Very slow growth
Small leaves, weak stems
Not suitable for long-term plant health

MODERATE LIGHT

75-150 foot-candles

Sustained but slow growth
Leaves remain smaller
Color and variegation may fade

BRIGHT, INDIRECT LIGHT

150-300 foot-candles

Ideal range for most houseplants
Healthy growth and leaf size
Best balance of vigor and safety

HIGH INDOOR LIGHT

300-500+ foot-candles

Suitable for acclimated plants
Faster growth and larger leaves
Requires careful watering and airflow
Risk of leaf scorch if direct sun is involved

What "bright, indirect Light" Actually Means

Bright, indirect light means:

Close to a window
No strong, direct sun hitting the leaves during peak hours
Light is filtered, reflected, or diffused

It does NOT mean:

Across the room
In shade far from windows
Any bright-feeling room

Distance matters. Light drops rapidly as you move away from any light source.

direct sun vs indirect light

Direct sun means the sun’s rays hit the plant directly. Indoors, this is most intense:

Near south- or west-facing windows
During midday and afternoon

Many houseplants tolerate brief or gentle direct sun, especially:

Morning sun
Winter sun
Filtered sun through sheer curtains

Prolonged, harsh direct sun can scorch leaves, particularly variegated or thin-leaved plants.

Grow Lights

Grow lights can fully replace or supplement window light when used correctly.

Some considerations to keep in mind:

Measure light at plant height
Provide 10-14 hours of consistent light (We almost always do 12 hours)
Avoid placing lights too close without measuring

You may find a light that has low intensity, say 30 foot-candles for example, so you decide to try to make up for that lack of intensity with a longer duration. Unfortunately, longer duration cannot compensate for insufficient intensity. Both matter!

Here are some grow lights that we have used and have found to be excellent:

LBW LED Floor Grow Light C0284
Barrina T8 30W Full Spectrum Lights (for shelves)
Sansi BR30 40W Grow Light
Sansi 10W Clip-on Grow Light (good for smaller areas or on cabinets)

light and plant behavior

When light is insufficient, plants may:

Stretch toward light (leggy growth)
Produce smaller leaves
Lose variegation or color
Drop older leaves
Develop weak root systems

Increasing light often resolves multiple “mystery” problems at once. This is especially common with plants suddenly dying “without reason” whenever they get repotted. Most times, that plant is already stressed from lack of light, and repotting it pushes it over the edge and it can no longer cope.

consistency matters more than perfection

Plants adapt to stable conditions. A consistent, adequate light level is far more important than chasing ideal numbers.

Frequent changes in placement or light intensity often do more harm than slightly imperfect conditions. For example, rotating plants so that they grow more straight is only forcing the plant to exert more energy to continue chasing the light. This is generally not ideal, and there are some plants that absolutely should not be rotated (e.g. Monstera deliciosa).

Final Notes

Light drives everything else in plant care. Once light is correct watering becomes easier, soil stays healthier, and growth becomes predictable. Understanding and measuring light transforms plant care from guesswork into a repeatable system.

Roots & Tendrils