Homegrown StoreBlogGrowing IndoorsHow Much Light for Weed Seedlings? All about Cycles, Distance and Intensity

How Much Light for Weed Seedlings? All about Cycles, Distance and Intensity

how much light for cannabis seedelings

Knowing how much light weed seedlings need plays a key role in maximizing plant growth. Weed seedlings are generally delicate and have stringent illumination and nutrient requirements during this stage.

While insufficient rays cause seedlings to stretch and grow thin, too much light may burn them or stunt their development. Provide adequate illumination to increase their survival rate, cultivate healthy plants, prevent legginess, and get better yields.

What’s the best illumination type and intensity for seedlings? How much light do weed seeds need to germinate? Discover the ideal light schedule and intensity for cannabis seedlings below.

How much light do weed seedlings need?

Marijuana seedlings are delicate and require modest illumination to grow optimally. Excess lighting can damage their new foliage and dry out the soil. The first step to providing the right amount of rays is to create a proper marijuana seedling light schedule.

If you’re cultivating indoors, growing weed under natural light isn’t advisable. Get grow lamps to help your plants develop properly. 

As the baby crops develop, keep the light intensity low so that it doesn’t burn the new leaves. Make sure the lamps aren’t too close to the seedlings in your indoor grow.

cannabis seedling

The ideal light schedule for weed seedlings is 18/6, 20/4, or 24 hours of light daily. This cycle allows them to receive rays for several hours every day.

It also ensures your plants get enough illumination to grow but can still rest for some periods. Continue this light time sequence for about 10–14 days.

Some growers experiment with how much light a weed seedling gets by trying a 16/8 cycle. The schedule may affect plant growth and cause certain seedling problems, such as slow seedling growth, yellowing in leaves, falling over, light or heat stress.

Ideal cannabis seedling light intensity

The best cannabis seedling light intensity is about 100–300 μmol/m²/s. Since this PPFD level is neither too high nor too low, it helps budding plants achieve their potential growth.

At the seedling phase of growth, the light intensity on various parts of their canopies may differ. Varying areas in the tent may also receive different illumination levels.

Use an adjustable dimmer that allows you to lower the intensity of light when necessary. Otherwise, raise the lamp and keep it further away from your young plants.

cannabis seedling problems

How far should light be from weed seedlings?

What is the recommended light distance for weed seedlings? The exact answer depends on the type of lamp you use and the illumination intensity. While some lighting sources should be far from your plants, others work well when they’re close.

The ideal distance between the light source and the tallest plant canopy is around 1–3 feet. This placement lowers illumination intensity and enables the crop to grow at the right pace.

As you consider how far light should be, pay attention to the illumination power too. The higher the wattage of the lamps, the farther the cannabis seedling light distance should be.

The light model, diode spacing, and bulb size could impact the ideal distance between seedlings and lamps in your indoor growing setup. Certain manufacturers ease this problem by indicating the light height in the manual.

Best lights for weed seedlings

Although different types of grow light for indoor plants are available, fluorescents and LEDs are typically the best lights for weed seedlings. They provide enough illumination for delicate crops without burning them.

Fluorescent lights

Fluorescent lights are a great option if your grow tent or room is small. They don’t need special tools to use in indoor settings, so they’re easy and quick to install. These lamps are also readily accessible for growers.

Compact fluorescent lamps (CFLs) and tubes are the two main forms of fluorescent lights. Both are efficient for cultivating weed, and you can implement them easily as you build an indoor grow room.

This illumination type has a wide range of color temperatures and wattage levels. These factors decide the light distance for weed seedlings. Fluorescent lamps don’t use a high amount of energy, making them suitable for growers that want to conserve energy.

Although fluorescent lights are affordable, they’re not cost-effective in the long run in commercial settings. Their lifespan is short, forcing cannabis cultivators to change them after a few harvests.

Most fluorescent lamps have low lighting output, making it difficult to use them in a large area. They’re only good for growing a few plants at once.

cannabis seedling

Light-emitting diode (LED) lamps

Germinating weed seeds under an LED lamp is another great choice for weed growers. This grow light produces more illumination but less heat than other options. As a result, it’s more energy-efficient and sustainable than fluorescents.

When using LED lamps, make sure they don’t provide too much illumination for your budding cannabis plants. Target 20–40 watts per square foot.

Although these lights for cannabis seedlings have a high initial purchase cost, they’re cost-effective in the long run. Since they have a relatively low operating temperature, high-quality LED lamps can last for more than 50,000 hours.

LEDs are also ideal for cultivating several marijuana plants at once. Regardless of how much light cannabis seedlings need, these lamps offer enough illumination. This makes them an excellent choice for commercial growers as they suit the light schedule for weed growth stages.

Compared to other types of grow lights, LEDs emit fewer UV rays, which are potentially harmful electromagnetic radiations. This means that using LED lamps reduces the risk of health problems for your crops.

Provide a blue light spectrum to seedlings and vegging plants to promote growth and shorten inter-nodal spacing. When your crop starts to bloom, it requires a red spectrum for optimal development.


Do you have any queries about the ideal light for cannabis seedlings? We’ve answered common questions below.

Are LED lights too strong for seedlings?

An LED light isn’t too strong for seedlings, provided you ensure its intensity isn’t excessively high. Place the lamps at least two feet away from the plant canopy.

best light for weed seedlings

Can seedlings get too much LED light?

Seedlings can get too much LED light if the lamp is too bright or too close to them. Find out how much light weed seedlings need and leave some distance between them and the illumination source.

Should I dim my LED grow lights for seedlings?

Since seedlings are delicate, they may be damaged by excessively bright LED grow lights, so dimming could be helpful. It reduces the amount of rays that reach your seedlings. Buy dimmable lamps for easy control.

Which light spectrum is best?

The blue light spectrum is the best for weed seedlings as it produces wavelengths that aid plant growth.

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