For many years, fluorescent shop lights were the go-to seed starting bulbs for gardeners, but LEDs have quickly replaced them as the standard choice. LEDs are usually more expensive than fluorescent bulbs, but they are very energy-efficient and long-lasting.
Sowing seeds indoors under fluorescent lights is the easiest way for the home gardener to control growing conditions and grow healthy transplants. Incandescent bulbs give off more heat and less light (mostly red) than fluorescent tubes and will not produce good transplants by themselves.
The only benefit of grow lights before germination is that they can provide extra warmth which helps speed up germination. Germinating seeds at room temperature or slightly warmer is sufficient for most seeds, and some gardeners use a temperature-controlled seedling heat mat if they need extra heat.
630-660 nm (Red) Light: This light is essential for germination and stem growth, as well as leaf expansion. It is also used to regulate periods of growth and flowering. Too much red light, or red light used alone, will produce tall plants that appear stretched with thin leaves.
Fluorescent or LED Lights
For most home gardeners, a plug-in shop fluorescent or LED light fixture is the perfect type of light to use for seed starting. When shopping for fluorescent lights, look for high-output, full-spectrum (sometimes called “daylight”) bulbs.
Red light stimulates vegetative growth and flowering (but if a plant gets too much, it will become tall and spindly). Blue light regulates plant growth, which makes it ideal for growing foliage plants and short, stocky seedlings (but too much will result in stunted plants).
Typically, plants use more blue and blue-green light when they are seedlings, and more red light later on in their life cycles when they begin to flower and produce seeds.
Where Should Grow Lights Be Located? For seedlings, LED grow lights should generally be mounted between 24-36 inches above the plant canopy – however, this depends on the power (wattage) of the light source.
Seedlings need 14-16 hours of light every single day, without fail. Don't leave them on for 24 hours a day though. Like us, they need to rest at night. So plan to keep your artificial lights on for 14-16 hours during the daytime, and turn them off overnight.
Seedlings need more light than full grown plants, ideally as much as 16-18 hours a day. Additional light may be required for seeds started during the winter months. Affordable plant lights can be found at many garden supply stores for less than $100.
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
Once sprouted, most vegetable seedlings and other garden plants require at least 12 hours of good light per day, along with 8 hours of darkness. However, seedlings will grow the best when provided 14 to 16 hours of light.
Most indoor seedlings will need to be watered twice daily. Meanwhile, seedlings planted outdoors may not need as much attention. Watering your outdoor seedlings once a day or every other day may be enough, especially if it always rains in your area.
The amount of light each seedling needs will vary from plant to plant. Those that require less light at an adult stage don't need as much as those that enjoy full sun throughout their life cycle. Seedlings exposed to too much light or heat will wither and die.
Yes LED lights can burn the leaves of the plants. High intensity LED lights can be too much for plants, especially when they are extremely close to the plants.
A good rule-of-thumb for LED grow lights is 40 watts of actual wattage per square foot of growing space for flowering medical or "high light" plants like tomatoes or peppers.
High Light Stress In Plants
If a plant is getting too much light and suffering from high light stress, its leaves may look as though they have burned or simply are falling off. In many cases, the soil will be dry to the touch, too.
If you want to keep your plants healthy and happy, then they must have the right amount of light. Dimming lights is a great way to provide just enough lighting for plants while still saving a little on energy costs.
LED grows lights should be placed from 14 to 30 inches above the plants. One of the biggest advantages of using LEDs is that they put off so little heat. So, you can place them close to your plants without worrying about burning them.
Most of the seeds germinate best in dark environments. The presence of light tends to inhibit their growth. The light decomposes carbonic acid gas and expels oxygen which leads the seed to harden. These gases are key factors that promote germination.
Blue Light
Effective chlorophyll production makes leaves lush and green. Plants need blue light to grow thick, sturdy stems and healthy leaves.
Blue light helps plants produce chlorophyll, the pigment they need to grow. It also helps encourage germination and root development in young plants and seedlings. Red light regulates plant growth and helps plants produce flowers and fruit.
Blue: This is the most important light for plant growth. It is easy for chlorophyll to absorb and convert into energy. Red: As the second most important wavelength, red light is incredibly potent for plants when combined with blue light.
Before your seedlings germinate, the easiest way to water smaller, shallowly planted seeds is with a mister or very gentle spray bottle. Using a watering can or hose without a mister can displace smaller seeds and can make it easy to over-water.