When it comes to plant care, light is the most underestimated factor — particularly indoors and even more so during winter.

Many homes feel bright. Our eyes adjust quickly, our brain compensates for contrast and brightness, and everything looks fine. But plants don’t experience light the way we do. They respond to light as it physically is, not as we perceive it.

This article explains why indoor light levels are usually much lower than expected, how fast light drops with distance from a window, and why winter makes this effect even stronger.

1. Why Our Eyes Misjudge Light

The human visual system is incredibly adaptive. Walk from a sunny street into a living room and within seconds your brain recalibrates brightness, contrast and colour balance. That’s why indoor spaces can feel perfectly bright — even when light levels are objectively low.

A camera tells a different story.

Anyone who has ever taken photos indoors knows this:

• ISO values need to be pushed up

• shutter speeds become much slower

• noise increases compared to outdoor shots

That’s because a camera measures light objectively. It doesn’t adapt.

Plants behave in the same way. They don’t compensate for low light. The amount of light that reaches the leaves is exactly the amount of energy available for photosynthesis.

Perception is not measurement.

2. Outdoor Light vs Indoor Light

To understand how big the difference really is, it helps to look at outdoor light levels first.

Typical outdoor light levels (for reference)

• Summer, sunny: 60,000–100,000 lux

• Summer, overcast: 10,000–20,000 lux

• Winter, overcast: 1,000–5,000 lux

Even on a grey winter day, outdoor light levels are often higher than what many indoor plants receive.

Once light passes through windows and enters a room, a large part of it is lost:

• glass filters and reflects light

• the sun is lower in winter

• light enters from one direction only

• walls and furniture absorb rather than reflect usable light

3. How Fast Light Drops Indoors (Summer vs Winter)

Light intensity decreases much faster indoors than most people expect.

Below are approximate values for indirect daylight in a typical home in Belgium or Northern Europe.

Indoors – indirect daylight

Summer:

• At the window: ~5,000–10,000 lux

• 1 m away: ~1,000–2,000 lux

• 2–3 m away: ~200–500 lux

Winter (same spot):

• At the window: ~1,000–2,000 lux

• 1 m away: ~200–500 lux

• 2–3 m away: ~50–150 lux

Especially in winter, what feels like a bright room often corresponds to deep shade for a plant.

For many tropical houseplants, light levels below a few hundred lux mean maintenance mode rather than active growth.

4. Why Winter Makes Everything Harder

Winter doesn’t just mean colder temperatures. From a plant’s perspective, it also means:

• shorter days

• a much lower sun angle

• less total daily light energy

• slower photosynthesis

Even if temperature and watering are kept stable, light often becomes the limiting factor. Growth slows down not because something is wrong, but because there simply isn’t enough energy available.

5. Greenhouse Light vs Living Room Light

Our plants are grown in Belgium without artificial lighting. They are adapted to moderate light levels.

But there is an important difference between a greenhouse and a living room:

• In a greenhouse, plants receive natural daylight from all directions

• Light is more evenly distributed

• The total daily light input is much higher, even in winter

Indoors, light comes from one direction only, and intensity drops rapidly with distance from the window.

This is why a plant that thrived in the greenhouse can slow down noticeably once placed indoors — especially in winter.

6. What This Means for Plant Care

If your plant slows down during winter, light is often the main limiting factor — not water, not nutrients, not care mistakes.

A few practical takeaways:

• distance to the window matters more than most people think

• winter light indoors is much weaker than summer light

• moving a plant closer to the window can already make a measurable difference

• slow winter growth is normal and expected

Plants don’t rush. They respond to the light they receive.

Understanding indoor light helps set realistic expectations — and leads to healthier plants in the long run 🌱

Want to measure light levels more precisely?

In this article we explain the difference between lux and PAR, and how to use a light meter to evaluate indoor light conditions for your plants: