How Much PPFD For Indoor Plants In Each Growth Stage?

LED grow lights are becoming increasingly popular, especially among indoor growers. The massive adoption of LED grow lights came with several unfamiliar terms. Some of these include color temperature (K), Photosynthetic Active Radiation (PAR), Photosynthetic Photon Flux (PPF), Yield Photon Flux (YPF), and the most talked about of them all, Photosynthetic Photon Flux Density (PPFD).

This article looks closely at PPFD for plants – what it is, why it is essential, how it is measured, and the right amounts of PPFD for indoor plants.  Let’s start with understanding what PPFD is.

What is PPFD, and how is it measured?

Most farmers are familiar with LED grow lights, but only a few know what PPFD is. The Photosynthetic Photon flux (PPFD) is the number of Photosynthetic Active Radiation (PAR) photons (the type of light that supports photosynthesis in plants) landing on a specific surface area each second.  

In simpler words, it is a measure of the amount of photosynthetic light reaching your plant canopy, and how well those lights work in terms of their output.  PPFD for plants is measured in µMol/m2/S (micromoles per square per meter per second).

Why do we measure the best PPFD for plants?

Like sunlight is to outdoor plants, grow lights are to indoor plants. LED grow lights are powered by LED chips, and they provide the light energy and “food” required for photosynthetic activities in plants. As a result, plants can stretch, develop, flower and bear fruit, and we can get the colors, unique shapes or flavors, nutritious fruits, or flower buds full of special substances that we want from indoor plants.

LED grow light manufacturers typically compute PPFD charts or data for each grow light model they release. But that doesn’t mean the light is right for the plants you’re growing – their PPFD output may exceed the plant’s maximum requirements and be prone to scorching, or it may simply not meet the plant’s optimal growth requirements resulting in poor plant form and color, or dramatically reduced yields.

Therefore, growers need to determine the PPFD requirements of their plants and then purchase a grow light with a PPFD output that meets those requirements.

Recommended PPFD Data for Common Plants

The recommended PPFD levels for plants differ across plant types and growth stages. For example, the PPFD levels for flowering or fruiting plants are often higher than PPFD levels for leafy green plants. While PPFD for weed plants and tropical plants is much higher than for ordinary plants.

Interestingly, the value of PPFD that can be absorbed by plants varies under different environments. For instance, indoor weed plants growing at optimal PPFD levels may experience limited growth when given more intense light.  However, by introducing CO2 supplementation to neutralize low levels of CO2, plants can withstand up to 2,100 µMol/m2/S PPFD and up to 36 Degrees Celsius of temperature. Using CO2 in your indoor grow area increases the rate of photosynthesis and guarantees 20-30% more yield and a 15% increase in growing speed.

Based on popular data, here are some recommended PPFD levels for common plants at different growth stages;

1. PPFD for Weed Plants

Weed plants require 16 hours of light during their vegetative stage and 12 hours at the flowering stage. As mentioned earlier, a grower can either supplement CO₂or not. 

For regular weed growing, the PPFD for seedling stage is 100-300 µMol/m2/S; the PPFD for vegetation stage is 400-600 µMol/m2/S, and the PPFD for flowering stage is 800-1,000 µMol/m2/S.

When the CO₂ supplement in weed growing, the PPFD in the seedling stage is 100-300 µMol/m2/S, while the vegetative stage requires 800-1000 µMol/m2/S PPFD and 400-800 ppm CO₂. The flowering stage requires 1,000-1,500 µMol/m2/S PPFD and 800-1400 ppm CO₂.

It is best to consult an expert grower before supplementing carbon dioxide when growing indoors. Sometimes, the increased inputs due to the use of CO2 may not justify the outputs you desire.

2. PPFD for Cucumbers and Tomatoes

Growing cucumbers and tomatoes indoors require about 12~16 hours of artificial light. To get the maximum yield and pleasant flavor, we recommend 16 hours of indoor lighting. The ideal PPFD for the seedling stage is 100-200 µMol/m2/S, 200-500 µMol/m2/S for the vegetative stage, and 500-600 µMol/m2/S for the flowering and fruiting stage.

Alternatively, if you prefer a 12 hours light schedule, don’t make the PPFD figure exceed 800 µMol/m2/S, just increase it by around 50~100 µMol/m2/S for each stage as long as you can keep your plants well managed in a cycle of heat handling and watering.

3. PPFD for Pepper Plants and other Flowering Plants

Indoor flowering plants also require an average of 12~16 hours of light. The ideal PPFD for plants in this category is between 100 and 300 µMol/m2/S for the seedling stage. It gets slightly higher for the vegetation and flowering stages – 300-600 µMol/m2/S and 600-750 µMol/m2/S, respectively.

Please avoid applying this PPFD to shade-loving plants. They will get sunburn under this intensity.

4. PPFD for Lettuce and Herb

Although edible greens like lettuce and herbs seem to require shorter periods of light, they have been proven to thrive in 16 hours of light and receive a 30% yield increase in this case. Their PPFD for the seedling stage requires 100 µMol/m2/S, while the PPFD for vegetative stage and mature stage requires 100-250 µMol/m2/S.  

A sweet figure of PPFD for lettuce and herb is 170 µMol/m2/S for either seedling or vegetative, till “eaten”.

To Round Up…

Urban farms and home gardens popping up, indoor plants need artificial light to live and thrive whether in days or at nights. Growers need to understand the indoor lighting requirements of their plants to ensure maximum growth and production, and PPFD is an efficient way of achieving this.  Carefully research PPFD maps before you invest in any LED grow lights.

Mars Hydro offers some of the best commercially viable LED grow lights for professional and hobbyist growers. The LEDs are equipped with the latest dimming feature for growers to easily manage the PPFD levels for their plants at different stages. Check here for efficient LED grow lights that meet your plants’ PPFD requirements.