Seedlings requires specific amounts of light to grow correctly. The amount of light that fall on a seedling will determine the quality of the seedling’s growth. Too little light will cause the seedling to have pale leaf and floppy growth due to the plants attempt to reach more light.
Too much light will bleach the leaf of the seedling as the light intensity is too high for the young seedling’s leaves. The amount of light that can be measured for a seedling is called Photosynthetic Photon Flux Density, or PPFD for short. PPFD measure the amount of usable light that falls on a square meter of the plant every second.
How Much Light Do Seedlings Need
Seedlings require a narrow range of PPFD requirements because seedlings does not have the large leaf surfaces and root system that mature plants have. Because of the lack of leaves and roots of seedlings, they cannot handle much light. Many plants has a specific PPFD range that they require during the seedling phase.
Plants such as tomatoes and cucumbers has higher PPFD requirements because they grow quick. Plants like leafy greens and herbs require less PPFD. Using a reference chart will show the PPFD requirements for different type of crops.
The light fixture that you use will also impact the PPFD that is provided to the seedling. Fluorescent lights are often used for seedlings because they produces little heat, and they naturally emit lower intensity of light. LED panels allow for better control of the light intensity for the seedlings but can easily provide to much light if they are set to full power.
High-intensity discharge lights are too high in strength for seedlings so they must be placed a distance away from the seedlings. Adjusting the height of the light fixture can adjust the PPFD that is provided to the seedling. Moving the light fixture away from the seedling will lower the PPFD that impact the seedling.
Increasing the proximity of the light fixture to the seedling will increase the PPFD that impacts the seedling. A person must also consider the Daily Light Integral, or DLI. While PPFD measurements will show light intensity, DLI will show the total amount of light that the plant will receive over the course of one day.
To provide the same DLI to the plants, a person could use lower PPFD settings for a longer amount of time, or provide higher PPFD settings for a shorter period of time. Both options will produce the same DLI if adjusted correct and will work for the seedling. The spectrum of the light will also impact the growth of the seedling.
The seedling require blue light wavelengths to encourage the plant to grow compactly and prevents the plants from stretching. The plant does require some red light wavelengths for the process of photosynthesis to occur. Using full spectrum white LEDs will provide the proper spectrum of light for the seedling.
Far-red light can be used for the seedling but in small amounts because too much far-red light will cause the seedlings to stretching. It is a common mistake to provide the same amount of light to all of the seedlings in a greenhouse or grow area. A basil seedling will not have the same PPFD requirements than a tomato seedling.
Using a light meter will allow a person to measure the PPFD that impacts the seedlings. When the seedling has grown its first true leaves, you can increase the PPFD by moving the light fixture closer to the plant or by increasing the power of the light. By providing more PPFD to the seedling by gradually increasing the light intensity the plant will be able to adjust to the change in light.
If provided with the proper amount of light, the seedling will exhibit thick stem and green leaves.