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How to Grow a Seed Inside With a Regular Light Bulb

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Indoor lighting provides a way to start seedlings indoors, even if you have poor window exposure or long, overcast days. Seedlings grow best when provided with light that provides both red and blue light wavelengths. Fluorescent full-spectrum lights work best because they provide the necessary wavelength and don’t heat up, but an incandescent light bulb can work in a pinch. Incandescent lights primarily supply the red spectrum. While heat from incandescent lights can pose a problem to plants, you can usually overcome this so the seedlings still produce strong early growth.

Sow seeds in seedling flats or pots set inside a drip tray. Most seedlings will germinate within seven to 14 days, and most will do so without light. When a seed variety does require light, it usually isn’t intense light. Place these near a sunny window or set them where they receive incandescent light for most of the day until they sprout.

Set the seedlings beneath the incandescent light fixture after they germinate. Adjust the height of the fixture so it sits at least 12 inches above the top of the seedlings so it doesn’t overheat the soil.

Place a thermometer at seedling level. Monitor the temperature throughout the day to ensure it doesn’t rise above 75 degrees Fahrenheit. Adjust the light’s height upward if the temperature begins to get too high.

Leave the light on for 14 to 16 hours daily, turning it off at night. Plug the light into an automatic timer to ensure it’s on for the correct amount of time.

Monitor soil moisture and water the seedlings when the soil surface dries. The soil may dry more rapidly under incandescent lights, so check it at least once a day.

Adjust the height of the light to maintain the 12-inch space between the light and the top of the seedlings as they grow.

  • If the seedlings have pale green foliage or fail to thrive, supplement the incandescent light with a cool-white fluorescent tube light or with natural sunlight.
  • Harden off the seedlings before transplanting them outdoors so they can adjust to the fuller spectrum of sunlight: Place them outside in a protected area and gradually increase their daily exposure to sunlight over a seven day period.
References
  • University of Vermont Extension: Indoor Lighting for Plants
  • University of California Extension: Seed Starting
  • University of Illinois Extension: Demystifying Indoor Grow Lights
Photo Credits
  • Ryan McVay/Photodisc/Getty Images
About the Author

Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington’s specialties include small business information, crafting, decorating and gardening.

How to Grow a Seed Inside With a Regular Light Bulb. Indoor lighting provides a way to start seedlings indoors, even if you have poor window exposure or long, overcast days. Seedlings grow best when provided with light that provides both red and blue light wavelengths. Fluorescent full-spectrum lights work best …

Can You Use Regular Light Bulbs As Grow Lights?

Last updated September 8, 2019 By Steven 50 Comments

Grow lights are expensive. Regular light bulbs are not.

This could be a great way to save money…if regular bulbs work for growing plants.

People often assume you need expensive grow lights to make up for the lack of natural light, but they’re wrong.

You can actually use regular light bulbs to grow plants indoors.

But should you use regular bulbs?

In some cases, yes; in some, no.

And when it comes to LEDs, you want to be careful. Some regular LED lights can work just fine as grow lights, but many are not suitable—see the LED section below for more.

Before we get into that, you might be asking yourself how you would know if your plants aren’t getting enough regular light and whether they need artificial light to help them out.

Believe it or not, your plants will tell you. Not literally, of course, but they will show you.

If your plants aren’t getting enough regular sunlight, they will grow tall with weak stems and the leaves will be lighter in color. New leaves will often be larger in size and the leaves on the inner part of the plant may start to turn yellow.

If your plants show these symptoms, you are going to want to get them some additional light.

The most successful light bulbs contain both blue and red wavelengths of light. The blue is especially useful for foliage growth and the red is for flowering and fruiting.

Types Of Light Bulbs Available

If you just need light for your regular houseplants, any lamp or light fixture will do.

Which one is best for you, depends on your needs (see the next section).

You do want to make sure the light you choose has the correct color temperature (explanation below in the fluorescent light section), as this drastically improves performance.

The most popular types of light bulbs to use as grow lights are incandescent or fluorescent bulbs, but you can also use LED lights, halogen lights and traditional horticultural grow lights, like high-pressure sodium bulbs (HPS) and metal-halide bulbs (MH). The first two are fine for small gardens; if you’re got a larger grow, LED or HPS/MH make the most sense.

If you are thinking of growing plants from seeds, you’d be best off with hanging tube fixtures that you can place directly over your plants. There are special kits available that include the fixture and reflectors.

Do Incandescent Grow Lights Work (i.e. Regular Bulbs)?

Incandescent lights are the standard light bulbs we all already have in our homes (here are a bunch of examples on Amazon).

They are the cheapest option, but they are inefficient.

They use more power to get the same output and they give off a substantial amount of heat. For these reasons, we generally do not recommend using them for your plants.

Take a look at the following graphic.

A comparison of incandescent, fluorescent and LED bulbs when used as grow lights for plants. Incandescent bulbs use the most power, last the shortest amount of time and provide the least amount of usable output for plants.

If you do use incandescent bulbs, make sure you don’t place them too close to the plants.

Use the hand test. Place the back of your hand where the plant is and wait a minute. If the light becomes too hot for your hand, it is also too hot for the plant and you need to move it further away.

Incandescent bulbs are usually the first option people consider, because they are cheap and we all already have some lying around the house.

But we always recommend fluorescent bulbs for small first-time growers.

They don’t cost all that much more and they are a lot more efficient: they last longer and use less power, so you actually end up saving money.

Can Regular Fluorescent Bulbs Be Used As Grow Lights?

Fluorescent lights are the best choice because they are the most economical.

They are sold in tubes (like these, which are good for larger indoor gardens) or compact bulbs that go into a regular lamp socket.

These are called CFLs and are best for a few plants or as supplemental lighting. They are the bulbs we will discuss from here on (everything we say goes for tubes as well, though).

Fluorescent lamps stay cool enough that they can be placed close to your plants and they use much less power per lumen (the amount of light they give off) than incandescent bulbs, which saves you on your power bill.

Many of us also have some at home already. That said, you want to pay attention to the color temperature of the bulb to ensure the best possible performance.

If you don’t mind spending a bit more, you can get a specialized fluorescent bulb (like these) made specifically for growing plants.

These have an optimized color spectrum for plants (see the next few paragraphs to help with choosing the right color temperature) and they are also more powerful than regular fluorescent bulbs.

Regular bulbs work just fine, though, especially if your plants are already getting some natural daylight. They key is to make sure they have the correct color temperature, measured in Kelvins.

How Many Kelvins Should A Bulb Have In The Vegetative Period?

Generic fluorescent bulbs and tubes are higher in blue wavelength light. This is great if you are growing plants that don’t bloom, like a cactus or herbs. It is also great for the vegetative period of blooming plants.

For vegging and for plants that do not bloom, use bulbs labeled as ‘daylight’ or ‘cool white’. The color temperature on these bulbs will be between 6000 K and 7000 K.

How Many Kelvins For Flowering?

If you are growing plants that flower or fruit, you will want a bulb with more reddish light. You can still just use regular bulbs, but you want to make sure they are labeled as ‘warm white’ or ‘soft white’ like these. In terms of color temperature, they will be between 2000 K and 3500 K.

Another option is to get a bulb with a color temperature right in the middle, between 4500 and 5500 K (confusingly, these are also sometimes labeled as ‘daylight’).

These work for all plants, but are not quite as efficient as cooler bulbs for growth or warmer bulbs for flowering. We find a mix of cold and warm bulbs to work best.

The main problem with both incandescent and fluorescent bulbs is that they aren’t generally powerful enough to flower more than a couple of plants, unless you get a ton of them. Once you get a lot of them, they are no longer cost effective, because there are much more efficient lighting options available. This article explains how many CFLs you need per plant.

If you have more than a couple of plants, you would be much better off with high-intensity discharge lights (HID) or LED lights.

Can Any LED Light Be Used As A Grow Light?

LED lights are more energy efficient and emit much lower levels of heat than other types of lighting. But can you use any led lights to grow plants?

But because LED technology is so customizable, every bulb is different and you want bulbs that produce the exact mix of red, blue and other wavelengths preferred by your plants.

White light contains a great mix for plants, so white LED bulbs will work to grow. The main issue is one of power. You need lights that give you sufficient output to flower plants and many regular bulbs will not do that.

Due to the lack of power and the potential for a less-than-ideal spectrum, many general LED lights are not as effective for plants as specialized ones.

On the other hand, if they provide sufficient output and a good color spectrum (like white light), they will work just as well as a specialized grow light, since they are basically the same thing.

If you are unsure and want to be certain you get a light that can both grow and flower plants, your best bet is to get a horticultural LED grow light that uses COBs. They are designed to produce the wavelengths used by plants in the ideal ratios, making them the best bloom LEDs available.

In general, you are better off purchasing these, as opposed to just general-use LED lights. They are not cheap, however. That said, there are a few quality, inexpensive LED plant lights on the market.

Can Plants Grow Under Halogen Lights?

Halogen lights also provide full spectrum light and are quite powerful, but they are similar to incandescent bulbs in that they emit a lot of heat and are not as energy efficient as fluorescent lights, HID lights or LED lights.

HID Plant Lights

Finally, we come to traditional horticultural grow lights (if you already know you want to go with HID lighting, head here for help in choosing the best bulbs). These are often referred to as HID lights and are further broken down into HPS and MH lights.

HPS bulbs emit more of a red spectrum light, making them superior for flowering and fruiting, while MH bulbs emit more blue light, making them ideal for plant growth.

HID bulbs are very energy efficient, but because they are so powerful, they still use a lot of power and emit a lot of heat. They also require additional components like a ballast.

Since they give off a large amount of light that is powerful enough to flower any plant, HID lights are still the light of choice for most commercial indoor growers, although LED lights are slowly taking that crown (read more about HPS versus LED lights).

For most of us, HID and LED lights are far too powerful and expensive for our needs. But if you have a larger garden, you’ll definitely want to go with one of these options. If you decide on HID lights, we have a post helping you choose the best HID system for your needs.

That post covers MH and HPS lights.

These days many people are opting for ceramic metal halide instead, since these lights combine MH and HPS in one bulb. We agree that CMH bulbs are far superior.

You can read more about CMH systems here, including our recommendations for the best ones.

How To Set Up The Lighting

For a small garden of a few plants in a room with very little natural light, a standing lamp with three bulbs and a movable or goose-neck feature works well. Use fluorescent bulbs with the highest wattage allowable by the fixture for the best results.

You want to aim the light towards the table with the plants. If your light fixture does have a movable arm, place the fluorescent bulbs closer to the plants than an incandescent bulb. This is to avoid heat damage, if using incandescent light.

To make more efficient use of the bulbs, place a reflective surface, such as a mirror or just some reflective foil, underneath the plants, so that the light can reflect back up towards the foliage.

And finally, attach and set a timer to run the lights for 14 to 16 hours a day. You can do this manually, but it is easier with a timer and even a quality one like this one doesn’t have to cost a lot.

Regular light bulbs can be used as grow lights, but some are better for horticultural use than others and LEDs are a special case. You need to…