Sometimes sun inhibits seeds that germinate in darkness. Some seeds don't need light to break through their seed casings and sprout. Most seeds germinate best with controlled amounts of UV generation, but there are seeds that germinate in the absence of light.
The only seeds that will germinate faster with light are the ones mentioned above in this article (or other seeds that require sunlight to germinate). Most seeds do not need grow lights until after they germinate. Most seeds germinate faster if they are warm.
Suffice it to say that it is mainly the light's effect upon a plant pigment called phytochrome within the seed. This relates to the type of light which the seed receives. As a generalisation, light in the red wave length usually promotes germination whereas blue light inhibits it.
Most seeds germinate best under dark conditions and might even be inhibited by light (e.g., Phacelia and Allium spp.). However, some species (e.g., Begonia, Primula, Coleus) need light to germinate (Miles and Brown 2007). Don't confuse seed light requirements with what seedlings need. All seedlings require sunlight.
Different seeds have different germination requirements. The relationship between light and plant growth is complex. Some seeds will germinate only in light, some in darkness and for some the requirement for light is related to the temperature.
Most seeds will not germinate without sunlight and will perform best with 12 to 16 hours each day. Indoors, place seed containers in a sunny, south-facing window and give the container a quarter turn each day to prevent the seedlings from overreaching toward the light and developing weak, elongated stems.
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.
All seeds need water, oxygen, and proper temperature in order to germinate. Some seeds require proper light also. Some germinate better in full light while others require darkness to germinate.
Most seeds germinate when the soil temperature is between 68° and 86°F. Once germination occurs, the optimum growing temperature for the seedling is about 10°F cooler than the optimum germination temperature.
Seed germination (or seed starting) is the process of growing plants directly from seeds instead of buying ready-grown plants. Sprouting seeds indoors is an effective way to increase the germination rate versus germinating seeds outdoors directly in the soil.
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.
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.
Light intensity can cause severe damage to your seedlings to the point where they die or are stunted.
Pre-Soaking.
This method could be the fastest way to germinate seeds. Place seeds in a shallow container in warm water and leave them for 16 to 24 hours (smaller for 16, bigger for 24). Remember not to expose seeds to temperatures higher than 80°F (26.6°C) and not to pre-soak seeds for more than 24 hours.
High temperatures over 90 can kill the plant inside the seed.
Move the container to a warm, draft-free spot where you can check it daily. Most seeds germinate best when the temperature is between 65 and 70 degrees Fahrenheit, but check the information on the seed packet for specifics.
Vegetable seeds will germinate at a wide range of soil temperatures. Most seeds prefer to germinate in a range between 60 and 90 degrees. Some seeds are so sensitive to soil temps that they won't germinate if the soil is too hot or cold.
Germination depends on several environmental factors, e.g., water, oxygen, temperature, and often light and nitrate as well. Of these, water is the most essential factor.
There are four environmental factors that affect seed germination: Water, Light, Oxygen, and Heat.
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.
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).
The majority of seeds grow most effectively in the dark. Light, which is essential for seedling growth, may actually hinder the germination process. The three primary and necessary conditions for a seed to germinate are water, oxygen, and temperature. Thus, Light is not necessary for a seed to germinate.