How Much Light Do Your Indoor Plants Need? A Simple Guide to PPFD

Hey plant lovers! If you’re growing plants indoors, you’ve probably heard of grow lights. But did you know that not all plants need the same amount of light? And it changes depending on what stage they’re in?

Let’s talk about PPFD (Photosynthetic Photon Flux Density), which is just a fancy way of saying how much light your plants are getting. Don’t worry, I’ll keep it super simple and break it down so you know exactly what your plants need to thrive.

Why Light Matters

Different plants need different amounts of light, and it depends on whether they’re just sprouting, growing leaves, or making flowers and fruit. With grow lights, you can control the light strength and even tweak the colors (like red or blue) to make your plants happy.

Below, I’ll walk you through how much light (measured in PPFD, or µmol/m²/s) your plants need at each stage.

Light Needs for Different Growth Stages

Here’s the lowdown on how much light different plants need, based on what they’re doing:

1. Tissue Culture (Baby Plants in a Lab)

For plants grown in a lab-like setup (think tiny plant babies in test tubes), you only need 40-60 µmol/m²/s. Most plants in this stage are good with this range. Not too bright, just enough to get them started.

2. Seedlings (Young Plants)

When your plants are just sprouting, they need a bit more light, 150-250 µmol/m²/s. Different crops might need a little more or less, but this is the sweet spot for most baby plants to grow strong without getting overwhelmed.

3. Vegetative Growth (Growing Leaves)

This is when your plants are bulking up with leaves. Here’s what they need:

Leafy Greens (like lettuce or spinach): 250-350 µmol/m²/s. Most greens are happy with around 250, but fast-growing ones like certain lettuces can handle more to speed things up.

High-Light Plants (like tomatoes, cucumbers, or medicinal herbs): 300-600 µmol/m²/s. These guys love more light to grow big and healthy.

4. Flowering and Fruiting (Reproductive Stage)

When your plants start making flowers or fruit, they’re hungry for light. More light means better harvests! Here’s the deal:

Normal Conditions (400 ppm CO2, no extra carbon dioxide): 350-600 µmol/m²/s. This works for plants like tomatoes or high-light herbs.

Boosted CO2 (1200 ppm): Crank up the light to 600-1200 µmol/m²/s. Extra carbon dioxide plus more light can seriously pump up your yield. Adding far-red or UV light can also make flowers pop more and improve the taste or active compounds in plants like medicinal herbs.

5. Succulents and Carnivorous Plants

For cool ornamental plants like succulents or Venus flytraps, aim for 250-350 µmol/m²/s. This keeps them colorful and healthy without overdoing it.

Converting PPFD to Lux (If You’re Curious)

If you’re using white-light grow lamps, you can roughly convert PPFD (µmol/m²/s) to lux (a measure of brightness). About 60-70 lux equals 1 µmol/m²/s. But heads-up: this only works for white lights. If your grow light has lots of red or blue (common in plant lamps), this conversion doesn’t hold up because the light spectrum messes with the math.

Let Us Help You!

Every plant and grow setup is different. Tell us what you’re growing and what your space is like, and we’ll hook you up with a custom light plan to make your plants thrive!