How to find out how much light your indoor plants need？

If you think plant care is all about watering and fertilising, you may be overlooking a crucial factor: lighting. For houseplants, not having enough light is like never having enough food - no matter how much they grow, they won't thrive.

Speaking of lighting, it's important to mention PPFD. 

What is PPFD? 

PPFD—that's Photosynthetic Photon Flux Density—might sound a bit technical, but it's really quite simple! PPFD measures the number of photons hitting a square metre of plant foliage per second. This handy little metric tells you whether your plants are enjoying enough sunlight.

It's so important to give your plants the right amount of light to thrive! Whether you're caring for succulents or your indoor herb garden, each plant has specific lighting needs. Without the right amount of light, plants can look weak, grow slowly, and even affect flowering and fruiting. Just as we need the right amount of food and water, plants need the right amount of light – not too much, nor too little.

PPFD Requirements for Different Plants 

It's so important to know the PPFD requirements of each plant if you want to adjust indoor lighting accurately. Plants fall into three main categories based on their PPFD needs: low-light, medium-light, and high-light plants. This classification is really helpful for choosing the right lighting intensity, depending on the type and growth stage of the plants.

• Low-light plants: These plants thrive in relatively low light conditions. Generally, a PPFD of 100-200 µmol/m²/s is sufficient. Common low-light plants include ferns, ivy, and some foliage plants like the dragon tree. These plants often grow under the shade of trees in their natural habitat, so they are adapted to lower light intensities.

• Medium-light plants: Require slightly higher PPFD values, generally between 200-500 µmol/m²/s. This category includes many indoor decorative plants, like African violets and some types of cacti. They need more light than low-light plants but cannot withstand direct sunlight.

• High-light plants: These plants need the highest PPFD values, typically between 500-1000 µmol/m²/s or more. This includes most fruit and vegetable plants, such as tomatoes, peppers, and most herbs. These plants require a lot of light during their growth phases to support rapid growth and fruiting.

• PPFD Requirements for Cannabis Plants: Cannabis plants, increasingly popular for medical and recreational use, have particularly unique lighting needs.

  In the germination and seedling stages, a recommended PPFD value is between 200-400 µmol/m²/s.

  As the plant enters the vegetative phase, the PPFD should increase to 400-600 µmol/m²/s.

  During the flowering phase, the PPFD needs of cannabis plants further increase, typically requiring 800-1500 µmol/m²/s to ensure ample energy for producing abundant flowers and resin.

If you're an indoor grower, it's really important to understand which category your plants fall into and what kind of lighting they need at different stages of their growth. The right PPFD not only helps your plants to grow, but it also stops them getting sick and encourages them to flower and fruit better!

Common Questions About PPFD

1. Do different plants have the same PPFD requirements?

   It's true that different plants have different needs when it comes to PPFD. This is because they come from different natural habitats, have different genetic traits and are at different stages of growth.
   
   Take, for instance, the lovely orchids and ferns that call the tropical rainforest understory home. These plants are perfectly adapted to low-light environments, so they don't need much light at all!
   
   On the other hand, plants that are native to open areas like deserts, such as cacti and some succulents, are adapted to high-light environments and thus require higher PPFD levels. It's also worth noting that even the same species of plant may have different PPFD needs during different life stages (e.g. growth phase, flowering phase).

2. What happens if PPFD is too high?

   It is a fact that excessively high PPFD can lead to several adverse effects, including leaf burn, chlorophyll degradation and reduced photosynthesis efficiency.

   High light intensity increases the surface temperature of leaves, causing rapid evaporation of water and exposing plants to both thermal and light stress.

   This prolonged condition can lead to photoinhibition, where the overall efficiency of photosynthesis declines due to excessive light intensity. Additionally, too high PPFD can disrupt normal plant metabolism, leading to stunted growth.

3. What if PPFD is too low?

   Too low PPFD can cause plants to grow slowly, hinder chlorophyll synthesis, and affect their photosynthesis and energy production.

   Plants in too low PPFD conditions may exhibit etiolation, where they abnormally elongate in search of light, leading to a fragile structure. Long-term insufficient lighting can also lead to reduced flowering, poor fruit development, or decreased yields.

4. How to adjust PPFD?

   Adjusting PPFD typically involves changing the distance between the light source and the plants, selecting the appropriate light intensity, adjusting the duration of lighting, or using reflective materials to improve light distribution. For instance, raising or lowering light fixtures can change。

   PPFD to suit specific plant needs. Additionally, using timers to control lighting duration can help simulate the natural day-night cycle, thereby adjusting light intensity. For environments that require precise control, like greenhouses or indoor cultivation, using adjustable intensity LED grow lights can provide more accurate PPFD control, optimizing plant growth conditions.

Note: Content reproduced from VANQ