Grow Lights for Seedlings – Everything You Need to Know

Lights for Seedlings

Starting plants from seed can be an advantageous process. Watching a tiny seed transform into a fully grown plant is almost magical. However, getting seeds to germinate and grow lights for seedlings requires providing the right conditions. One of the most important factors is making sure seedlings get enough light.

Why Seedlings Need to Grow Lights

Light is essential for seed germination and plant growth. It powers photosynthesis, allowing plants to produce food and energy. Seedlings need adequate light to develop properly.

Many factors can impact the amount of natural sunlight seedlings receive:

  • Starting too early – In many climates, there isn’t enough natural sunlight for seedlings in late winter and early spring. They need supplemental lighting.
  • Bad weather – Overcast and rainy periods block sunlight, leaving seedlings stressed. Grow lights fill in when nature doesn’t provide enough sun.
  • Short days – As seasons change, the hours of daylight decrease, limiting the light seedlings get. Artificial lighting extends the day’s length.
  • Indoor growing – For urban gardeners and anyone starting seeds indoors, grow lights are essential to substitute for the sun.

Without enough light, seedlings become leggy and weak as they stretch, looking for light. Their growth stalls leaves yellow, and they’re more disease-prone. Supplemental lighting prevents these issues and keeps seedlings robust.

Grow Light Options for Seedlings

There are many types of grow lights suitable for seedling. Here are some of the most common options:

Fluorescent Grow Lights

Fluorescent tubes or compact fluorescent bulbs (CFLs) are economical choices for starting seedlings. They don’t generate too much heat, making them safe for young plants. Look for “cool white” or “daylight” labeled bulbs that provide light ideal for seedling growth.


  • Inexpensive to purchase
  • Run coolly
  • Come in long tubes or compact bulbs
  • Emit light is ideal for seedlings


  • Need to be kept close to plants
  • Require replacing bulbs periodically
  • Don’t provide enough intensity for larger plants

LED Grow Lights

LED Grow Lights

LED grow lights have become famous for seedlings. They use very little energy but create intense light. Full-spectrum LEDs provide all the colors of light plants need. Panel-style LED lights are lightweight and easily positioned over trays of seedlings.


  • Energy efficient
  • Generate little heat
  • Produce full-spectrum light
  • Long-lasting bulbs
  • Lightweight panels


  • Higher upfront cost
  • Light distribution can be uneven

High-Intensity Discharge (HID) Lights

Metal halide and high-pressure sodium HID grow lights work well for seedlings but can also be used to grow plants to maturity. HID lights produce an intense light that penetrates deep into a plant’s canopy.


  • Very bright, full-spectrum light
  • Can support plants throughout their lifespan


  • Generate significant heat
  • Require hanging fixtures
  • Use more electricity
  • Bulbs need replacing

T5 Fluorescent Grow Lights

T5 fluorescents are a heavy-duty type of fluorescent lighting. T5s are brighter and more efficient than standard fluorescents. The T5’s elongated shape provides even light distribution. T5 fixtures feature multiple bulbs for expanded coverage.


  • Bright, uniform light distribution
  • Relatively cool operation
  • Reasonably energy efficient


  • It can be more expensive upfront
  • Bulbs still need periodic replacing

What to Look for in Grow Lights for Seedlings

With the variety of lighting options available, selecting the right product for your seedlings can be tricky. Here are the key factors to consider:

Full Spectrum Light

Plants use different wavelengths of light for other processes. They need a balance of blue and red spectra for healthy growth. Ensure grow lights deliver a full spectrum with wavelengths ranging from 400 to 700 nanometers. Calm white and daylight fluorescents or full-spectrum LEDs provide complete light.

Low Heat Output

Seedlings are susceptible to heat stress. Hot grow lights can dry out and burn tender young plants. Look for lights made to run coolly, like LED and fluorescent options. Avoid hot HID lights unless they can be positioned far above seedlings.


Raising and lowering grow lights is essential to keep them at the optimal distance from the tops of plants as they grow. Look for adjustable hangers and cords. Choose lightweight fixtures that are easy to reposition.

Even Light Distribution

Some grow lights concentrate light directly under the fixture, leaving surrounding areas dim. Seedlings do best with uniform lighting over the entire growing gardening area. Panels or multiple-bulb fluorescent fixtures distribute light evenly.

Energy Efficiency

Grow lights will operate for extended periods, so energy-efficient options save money. LED and fluorescent lights give you more lighting bang for your energy buck. Compare wattages when choosing grow lights.


Consider how long grow lights will last before needing bulb replacement. Fluorescent tubes and HID bulbs have shorter lifespans and require changing every year or two, while long-lasting LED grow lights typically operate for years before replacement.

Setup Guidelines for Seedling Grow Lights

Proper setup of grow lights is critical to success with seedlings. Here are tips for positioning lights:

  • Place lights 2 to 4 inches above seedlings. Use adjustable hangers to raise the lights as the plants grow.
  • Angle lights to provide even coverage over the whole growing area.
  • Position fluorescent tubes within a couple of inches of each other. Fewer inches between bulbs is required for broader coverage.
  • Keep LED panels close to bathe young plants in light evenly.
  • Providing seedlings with slightly too low vs. too high light is better. Intense overhead light can overheat and dry out small plants.

How Long to Grow Lights for Seedlings

How Long to Grow Lights for Seedlings

Seedlings require 16 to 20 hours of light per day. Provide at least 16 hours of supplemental lighting, extending daylight if needed. Don’t go overboard with more than 20 hours, as plants need periods of darkness.

Use a timer to automate the grow light operation. Set lights to turn on before natural light starts and shut off after sunset. This mimics honest day length. Adjust light timing as seasons shift. Seedlings don’t need light at night.

Monitor seedlings to watch for signs they’re receiving adequate lighting. Stretched, leggy growth indicates insufficient light. Healthy, compact plants show lighting is on the right track. Adjust duration as needed based on plant response.

When to Start Using Grow Lights for Seeds

Timing grows light use depends on when you start seeds:

  • Spring planting – Use grow lights 4 to 6 weeks before your last expected spring frost. This gives seedlings a head start on the summer growing season.
  • Fall/winter planting – Begin growing seedlings under lights in early fall, about eight weeks before you want to transplant them into the garden. Continue supplemental lighting through winter.
  • Early sowing indoors – Some gardeners start seeds early, like in January/February, for summer gardening. Use grow lights right from the start since there’s minimal natural light available.

The goal is to time seed starting so young plants get adequate growth before moving outdoors. Grow lights allow starting seeds sooner, giving seedlings a boost. Just make sure to harden off plants before transplanting.

Do Plants Need Darkness?

Yes, plants require periods of darkness as part of their natural cycle. Interrupted night cycles from excessive light can stress plants. Most seedlings do best with approximately 16 hours of light and 8 hours of uninterrupted darkness.

Dark periods allow plants time to undergo biological processes that don’t occur in light:

  • Respiration ramps up in the dark, providing energy.
  • Flowering plants initiate bud development at night.
  • Darkness triggers hormone production that spurs stem and leaf growth.
  • Beneficial antioxidant production increases during nighttime.

Darkness also activates dehydration protection mechanisms. Time without light lets seedlings conserve moisture and energy. A consistent day/night schedule supports strong, balanced growth.

Grow Lights for Different Types of Seeds

While most seedlings thrive under full-spectrum white light, some species prefer specific light wavelengths. Here are lighting guidelines for starting different seeds:

  • Leafy greens, herbs, and vegetables do well under daylight or cool white light in the 6000-6500K color temperature range.
  • Long-day plants like asters and sunflowers grow best with 14+ hours of light. Extend their photoperiod with grow lights.
  • Short-day plants, including chrysanthemums, need 12 hours or less of light. Keep supplemental lighting to the minimum for these.
  • Blue light boosts growth for cucumbers, onions, peppers, and tomatoes. 
  • Red light is ideal for salad greens and radish seeds. Add supplemental red spectrum light or use pink/purple grow bulbs.
  • Full-spectrum white light works for most seeds, supporting balanced development. LEDs or daylight fluorescents provide a complete range of light.
  • Ornamental flower seeds that need light for germination often respond best to fluorescent lighting. Keep bulbs close to the soil surface.

While not all plants have specific light needs, tailoring your grow lights to your seed varieties can give them an extra advantage. Observe how different seeds respond and adjust lighting as needed.

Grow Light Height for Different Growth Stages

As seedlings grow, raise lights accordingly:


Keep lights very close, just an inch above seeds once sprouted. Light penetrates the soil to spur germination. Cool white fluorescents or LEDs prevent overheating at this stage.

Seedling Emergence

When first true leaves appear, maintain lights 2 to 3 inches above the new growth. Seedlings are still short but proliferating under proximity lighting.

Active Growth

As seedlings reach 3 to 4 inches high, raise lights to 4 to 6 inches above plants. This prevents light bleaching of tender young leaves while delivering plenty of intensity.


When plants are ready to harden off and move outside, lift lights to 6 to 8 inches above them. More distance prepares seedlings for direct outdoor light levels.

Gradually increase spacing between grow lights and plants. Let foliage be your guide, keeping lights close but not too tight.

Troubleshooting Seedling Grow Lights

Troubleshooting Seedling Grow Lights

If your seedlings under grow lights aren’t thriving, some adjustments may be needed:

Leggy, stretched growth means the plants aren’t getting enough light. Lower the lights, use more bulbs, or switch to more intense fixtures.

Wilting, purpling leaves – Plants are cold-stressed. Raise lights or provide bottom heat sources to warm roots.

Yellowing lower leaves – Old leaves aren’t receiving enough light. Improve coverage or reposition plants.

Burnt leaf tips – Seedlings are too close to hot grow lights. Increase the distance between lights and plants.

Failure to thrive – Check light timer settings to ensure plants get adequate photoperiods. Repair any malfunctioning timers or bulbs.

Monitor seedlings and make lighting adjustments as needed for the healthiest growth. Constantly tweak setups to provide optimum light exposure.

Grow Lights for Seedlings – Final Tips

Here are a few final tips for success with grow lights for seedlings:

  • Shop for energy-efficient, cool running lights to suit your setup – a 4′ T5 fluorescent fixture or LED panel.
  • Use adjustable hangers to reposition lights as your plants grow taller quickly.
  • Set lights on a timer to automate consistent daily lighting schedules.
  • Keep lights close to plants, especially when they’re young and small.
  • Maintain ideal ambient temperatures in your grow space, around 70°F.
  • Ensure seedlings get adequate darkness for at least 6-8 hours per night.
  • Monitor plants and make lighting adjustments to keep them thriving.

Supplemental grow lights optimize seedling development, giving home-grown plants a healthy head start. Proper lighting transforms seed starting into a fruitful process culminating with thriving garden transplants.


From fluorescent tubes to LED panels, grow lights help seedlings thrive indoors and outdoors. Proper lighting is crucial for nurturing seeds into vigorous transplants ready for the garden. Matching the right grow lights to your setup and specific seeds boosts budding plants right from the start. Monitor young seedlings and adjust artificial lighting to maintain compact, healthy growth. With the proper grow light guidance, even urban and indoor growers can successfully raise vigorous plants from seed.

Frequently Asked Questions

Can I use a regular room lamp to grow seedlings?

You can use a standard incandescent bulb or lamp for seedlings, but it won’t provide the complete spectrum light plants need for robust growth. Specialized grow lights are a better option.

Are shop lights good for starting seeds?

Fluorescent shop lights work well, especially if you choose tubes labeled as “daylight” or around 5000-6500K color temperature. Position the tubes close together over seed trays.

When can I stop using grow lights on seedlings?

Once seedlings are ready to transplant outdoors, you can begin hardening them off. Slowly expose them to more natural light while reducing supplemental lighting over 7-10 days.

Do I need grow lights if I start seeds on a sunny windowsill?

Seeds may do fine without additional lights if the windowsill provides bright, direct sun for much of the day. Monitor seedlings closely and add grow lights if they become stretched.

Is it okay to start seeds outdoors without grow lights?

You can sow seeds directly in the garden once outdoor temperatures have warmed in spring. Just make sure to choose quick-growing varieties that will mature before frost. Avoid starting plants too early outside.

Author: Brielle Walker

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