Understanding Light Measurement for Indoor Plant Growth: Lumens vs. PPendants
How Many Lumens Does a Good Grow Light Need?
The number of lumens a good grow light should have varies based on the type of plants being cultivated and the size of the growing area. However, as a general guideline:
Seedlings and Vegetative Growth: 2000 to 5000 lumens per square foot.
Flowering Stage: 5000 to 10000 lumens per square foot.
It's important to consider the light spectrum as well, since plants benefit from specific wavelengths for photosynthesis. In addition to lumens, it is crucial to look for lights that provide a full spectrum which is ideal for all growth stages. LED grow lights are popular for their efficiency and low heat output, and often provide higher photosynthetic photon flux (PPF) ratings, which directly relate to plant growth.
Lumens: The Indoor Gardening Myth
Lumens is the number one indoor gardening myth that is used for measuring the light produced by plant growth lamps. While measuring light lumens is a common practice, it is primarily focused on how much light the human eye perceives, and does not accurately measure the light that drives photosynthesis.
From a scientific standpoint, the metric symbol for lumens is LM. It measures the total amount of visible light from a specific light source as perceived by the human eye. However, this does not reflect the light wavelengths that are crucial for plant growth.
Plants and humans evolve under the same light from the sun. However, the way they use this light is vastly different. Humans use up to the full spectrum of visible light for their needs, whereas plants have pigments that optimize specific wavelengths for photosynthesis. Therefore, lumens alone are not a suitable measure for the light needed for plant growth.
Measuring the light output of lumens is an artifact of the lighting industry itself. Manufacturers, primarily focusing on lighting for humans, publish specifications in lumens. Some countries even require bulbs to be rated based on lumen output, which indoor gardeners have adopted due to its availability and general accuracy until the introduction of more precise measurement methods.
Beyond Lumens: PPF and Full Spectrum Light
For indoor grow lights, especially LED lights, it is crucial to look beyond lumens and focus on photosynthetic photon flux (PPF). PPF measures the light that is actually available for photosynthesis, providing a more accurate metric for plant growth.
When evaluating grow lights, here are a few key things to consider:
Full Spectrum Light: Ensure that the grow light provides a spectrum that mimics sunlight, making it ideal for all growth stages. PPF Ratings: Higher PPF ratings correlate with better plant growth, as these lights provide more usable light for photosynthesis. Color Temperature: Different wavelengths can be beneficial at different stages of growth, so look for lights that can adjust to the specific needs of your plants.With traditional fluorescent lights, two four-foot bulbs would produce a total of 5 to 6 thousand lumens. Modern LED grow lights, especially high-performance models, can give off up to 12000 lumens per unit, making them far more efficient and effective for indoor gardening.
In conclusion, when it comes to indoor plant growth, it's time to move beyond lumens and focus on more precise measures like PPF and full-spectrum lighting. This will ensure optimal plant health and yield in your indoor garden.