Using Grow Lights for Seedlings and Indoor Growing

Learn how to use grow lights for seedlings and indoor growing. Discover how much light plants need, how long to run lights, and how to avoid leggy growth.

Growing plants indoors can be incredibly rewarding, but it also comes with challenges, especially when it comes to light. Whether you’re starting seeds for your garden or trying to grow herbs and vegetables indoors, natural sunlight from a window is rarely enough to produce strong, healthy plants.

Grow lights make indoor growing far more reliable. They provide consistent, bright light that helps seedlings grow sturdy instead of tall and leggy, and they make it possible to grow certain crops indoors even when daylight is short or unpredictable.

This guide focuses on using grow lights effectively for seedlings and indoor growing, including how much light plants need, how long to keep the lights on, how close the lights should be to seedlings, and how to recognize signs that plants are getting too much or too little light. Seed starting is the primary focus, but these same principles also apply to growing herbs and some vegetables indoors under lights.

If you’re looking for step-by-step instructions on building a grow light shelf, start here: How to Build a DIY Grow Light Shelf for Starting Seeds Indoors.

If you already have grow lights and want to use them with confidence, you’re in the right place.

What Grow Lights Do

Plants use light to make energy through photosynthesis. Grow lights provide plants with the light they need for photosynthesis when natural sunlight indoors isn’t strong or consistent enough.

Outdoors, this happens naturally as the sun rises, moves across the sky, and changes with the seasons. Indoors, that natural light cycle is interrupted. Even the brightest windows rarely provide enough consistent light for strong growth.

Grow lights fill that gap. They act as a reliable substitute for sunlight by providing plants with the light they need, when they need it, and for the right amount of time. Instead of stretching toward a window or growing unevenly, plants receive light directly above, encouraging balanced, compact growth.

For seedlings, this is especially important. Young plants need steady light to develop strong stems and healthy leaves. Without enough light, seedlings grow tall and weak, making them more likely to fall over or struggle once transplanted outdoors.

Grow lights also remove much of the guesswork from indoor growing. Cloudy days, short winter daylight hours, and seasonal changes don’t affect plant growth when lights are set on a timer. With a consistent light source, plants grow at a predictable pace, making indoor seed starting and growing far more dependable.

Types of Grow Lights for Home Gardeners

You don’t need complicated or commercial-grade lighting to grow healthy seedlings or indoor plants. For most indoor growing situations, there are just two main types of grow lights to consider: fluorescent and LED.

Fluorescent Grow Lights (Older, but Still Usable)

Fluorescent shop lights were my standard choice for seed starting for many years. They were inexpensive, provided adequate light for seedlings, didn’t produce much heat, and were easy to hang close to plants.

If you already have a fluorescent setup, it can still work well for starting seeds indoors. However, fluorescent bulbs and fixtures are becoming harder to find as they are gradually phased out, and replacement bulbs may be limited depending on your location.

LED Grow Lights (Current Standard)

LED grow lights are now the most common choice. They’re widely available, energy-efficient, and designed specifically for indoor growing.

LEDs provide bright, consistent light without producing excess heat, which allows them to be placed close to seedlings. They also last much longer than fluorescent bulbs and don’t require regular replacements.

Many LED grow lights are designed to fit standard shelving units and can be easily hung or linked together, making them ideal for seed-starting shelves and indoor growing areas.

If you are building or updating a grow light setup today, LED grow lights are the easiest and most reliable option.

How Much Light Do Seedlings Need?

Seedlings need bright, consistent light every day to grow strong and compact. When light levels are too low or inconsistent, seedlings stretch toward the light source, resulting in tall, weak, leggy plants.

For most seedlings grown indoors under lights, the goal is to provide enough light for steady growth, not to overwhelm them with intensity.

How Many Hours of Light per Day?

Most seedlings do best with 14–16 hours of light per day, followed by a dark rest period. This schedule mimics the long days of spring and early summer, when many garden plants naturally grow.

Using a timer makes this easy and ensures seedlings receive the same amount of light each day, even when daylight hours are short or the weather is cloudy.

More light is not always better. Leaving grow lights on 24 hours a day can stress plants and interfere with normal growth cycles. Seedlings benefit from a regular day-and-night rhythm.

How Close Should Grow Lights Be?

Grow lights should be kept close to the tops of seedlings so the light reaches the leaves at the right intensity.

For most LED grow lights, place the lights about 1–2 inches above the seedlings.
Adjust the height as the plants grow to keep the light close and even. Keeping lights close helps prevent stretching and encourages sturdy stems. If the lights are too far away, the seedlings will lean and grow tall as they search for more light.

Does Color Spectrum and Light Type Matter?

Grow lights are often labeled with terms like full spectrum, daylight, or specific color temperatures. While light spectrum does affect plant growth, you don’t need to overthink it.

For seedlings and most indoor growing, full-spectrum or daylight grow lights work very well. These lights provide a balanced range of light similar to natural sunlight and support healthy leaf and stem growth.

Many modern LED grow lights are already designed with seedlings in mind, so choosing a light labeled full spectrum or daylight (around 5000–6500K) is usually enough. Consistent light placed close to plants matters far more than fine-tuning individual colors.

Consistency Matters More Than Power

Seedlings don’t need extremely powerful lights to grow well. What matters most is consistent, even light delivered at the right distance for enough hours each day. A simple setup with lights placed close to the plants and run on a timer will outperform a stronger light that’s too far away or used inconsistently.

If you notice uneven growth, rotate your trays occasionally so all seedlings receive similar light exposure.

Signs Your Plants Are Getting Too Much or Too Little Light

Even with a good grow light setup, seedlings and indoor plants may need small adjustments as they grow. Paying attention to how your plants look will tell you whether the light is just right or needs tweaking.

Signs of Too Little Light

Plants that aren’t getting enough light will often show these symptoms:

• Leggy growth with tall, thin stems, and lots of space between leaves.
• Leaning or stretching toward the light source.
• Pale green or yellowing leaves.
• Weak stems that flop over easily.

If you notice these signs, move the lights closer to the plants, add an additional light if needed, or make sure the lights are on for the full 14–16 hours each day.

Signs of Too Much Light

While less common, seedlings and indoor plants can also receive too much light, especially if the lights are too close or left on too long.

Watch for:

• Bleached or faded leaf color.
• Dry, papery, or scorched-looking spots on leaves.
• Leaves curling downward or appearing stressed.

If this happens, raise the lights slightly or reduce the number of hours the lights are on each day.

What Healthy Growth Looks Like

When light levels are right, seedlings should:

• Grow compact and sturdy.
• Develop strong stems.
• Have healthy green leaves.
• Grow evenly without leaning or stretching.

Indoor plants grown under lights should show steady, balanced growth rather than rapid stretching or stress.

Make Small Adjustments as Plants Grow

Plants change quickly, especially seedlings. A setup that works one week may need minor adjustments the next. Raising lights as plants grow, keeping trays evenly spaced, and watching for changes will help you dial in the right light levels.

Using Grow Lights Beyond Seed Starting

While grow lights are most often used to start seedlings, they can also be used to grow edible plants indoors from seed to harvest. The key is choosing plants that thrive in indoor conditions and understanding that growth may look a little different than it does outdoors.

Growing Herbs Indoors with Grow Lights

Many culinary herbs grow very well indoors under grow lights, especially leafy herbs that are harvested regularly.

Herbs that perform well under lights include:

• Basil
• Cilantro
• Parsley
• Oregano
• Chives
• Dill
• Mint

Place grow lights close to the tops of the plants and keep them on for 14–16 hours per day. Regular harvesting encourages bushier growth and helps prevent plants from becoming leggy.

If you’d like to learn more about herbs that thrive indoors, along with tips for care and harvesting, see this guide: Grow Herbs Indoors: Herbs that Thrive Inside.

Woody herbs such as rosemary and thyme can be grown indoors, but they grow more slowly and benefit from very bright light. These herbs often do best when grown under lights for part of the year and moved outdoors when conditions allow.

Growing Vegetables Indoors with Grow Lights

Some vegetables are well suited to indoor growing under lights, especially fast-growing or compact crops. Freshly harvested lettuce, spinach, and radishes are a treat in the middle of winter.

Good choices for indoor growing include:

• Leafy greens like lettuce, spinach, and arugula
• Asian greens like bok choi and Chinese cabbage
• Radishes and baby beets
• Microgreens

These crops grow quickly, don’t require pollination, and tolerate indoor conditions well.

For a deeper look at what works best indoors and how to set up an indoor vegetable growing space, see: How to Grow Vegetables Indoors.

Fruiting crops such as tomatoes, peppers, and cucumbers generally need much stronger light and more space than most home grow light setups provide. While it’s possible to grow them indoors, they’re usually better suited to outdoor gardens once they’ve passed the seedling stage.

Simple Grow Light Setups for Home Use

You don’t need a complicated or expensive system to use grow lights successfully. The best setup is one that fits your space, is easy to manage, and provides consistent light close to your plants.

Below are a few common grow light setups that work well for seedlings and indoor growing.

Single-Shelf or Tabletop Setup

A single grow light placed over a table, counter, or shelf works well for:

• Starting a few trays of seedlings.
• Growing herbs indoors.
• Small indoor growing projects.

For this type of setup:

• Use a light that spans the width of your growing area.
• Hang or mount the light so it can be adjusted as plants grow.
• Keep the light close to the plants and run it on a timer.

This is a great option if you’re short on space or just getting started.

Multi-Shelf Grow Light Setup

If you start a lot of seeds or want to grow plants indoors more consistently, a multi-shelf setup offers much more flexibility.

Wire shelving units with grow lights hung above each shelf are ideal because:

• Lights can be raised and lowered easily.
• Multiple trays can be grown at once.
• Space is used efficiently.

For standard 4-foot wire shelving, two 4-foot LED grow lights per shelf provide even coverage across seed trays and help prevent uneven growth.

If you’d like step-by-step instructions for building this type of setup, see: How to Build a DIY Grow Light Shelf for Starting Seeds Indoors.

Keep It Simple and Adjustable

No matter which setup you choose:

• Place lights close to the tops of plants.
• Use a timer for consistent light each day.
• Adjust light height as plants grow.

A simple, adjustable setup will outperform a more complex system that’s difficult to manage.

Growing Indoors with Grow Lights

Using grow lights doesn’t have to be complicated. Once you understand how much light plants need, how close lights should be, and how to watch for signs of stress or stretching, indoor growing becomes far more predictable and enjoyable.

For seedlings, consistent light early on makes all the difference. Strong stems, compact growth, and healthy leaves set plants up for success long before they head outside. The same basic principles also apply to growing herbs and certain vegetables indoors: Keep the lights close, provide steady light each day, and adjust as plants grow.

Whether you’re starting seeds for your garden, growing herbs in the kitchen, or growing greens indoors during the winter months, grow lights give you control over one of the most important factors in plant growth.

If you’re ready to grow something, these guides will help you take the next steps:

• How to Build a DIY Grow Light Shelf for Starting Seeds Indoors
• How to Start Seeds Indoors (10 Steps for Strong, Healthy Seedlings)
• Grow Herbs Indoors: Herbs that Thrive Inside
• How to Grow Vegetables Indoors

With the right light and a simple setup, you can grow healthy plants indoors no matter the season.

Good planning is key to a successful vegetable garden

Whether you are new to growing your own food or have been growing a vegetable garden for years, you will benefit from some planning each year. You will find everything you need to organize and plan your vegetable garden in my PDF eBook, Grow a Good Life Guide to Planning Your Vegetable Garden.