Grow Lights for Indoor Plants Explained

You need a grow light if you want to start seedlings, grow salad greens, or keep herbs productive indoors, but not for microgreens, sprouts, or low-light houseplants. According to Utah State University research, modern LED grow lights deliver roughly 2.5 to 3.0 micromoles per joule, two to three times the efficiency of older fluorescent tubes, so a good light now costs very little to run. For most home gardeners, a simple LED shop light is all it takes.

Do You Actually Need a Grow Light?

Start by asking what you want to grow, because for many plants the answer is that you do not need one at all.

You do not need a grow light for: microgreens (they finish in 7 to 14 days on a windowsill), sprouts (no light needed), and forgiving low-light houseplants like snake plant, ZZ plant, and pothos. In a bright south or east window, these do fine on daylight alone.

You do need a grow light for: starting vegetable seedlings, growing lettuce and salad greens to harvest, and keeping herbs like basil productive through the darker months. These plants need more consistent, intense light than a California window provides, especially in winter.

The reason comes down to how much light a window actually delivers. According to University of Illinois Extension, outdoor sunlight measures 10,000 to 12,000 foot-candles, while indoor light near a window is only 2,000 to 5,000 foot-candles at best and often far less. Here in Santa Cruz County, coastal fog and the low winter sun angle shrink that further for weeks at a time. A grow light fills the gap with a steady, controllable source that does not care whether it is foggy in Capitola.

What Types of Grow Lights Are There?

Three types show up in home gardening, and for nearly everyone the choice is now simple.

LED (the default choice)

LED grow lights are the standard recommendation today. According to Utah State University research, quality LEDs achieve roughly 2.5 to 3.0 micromoles per joule, meaning they turn more of your electricity into usable plant light than any older technology. They run cool, last for years, and come in inexpensive shop-light and clip-on forms. For a home gardener starting seeds or growing greens, an LED is almost always the right pick.

Fluorescent (still fine, being phased out)

Fluorescent tubes, especially the slim T5 type, were the old standard and still work well for seedlings and greens. According to Utah State University research, quality T5 fluorescents deliver only about 1.0 micromole per joule, less efficient than LED but perfectly capable. The catch is they run warmer, wear out faster, and the tubes are increasingly hard to find as manufacturers shift to LED. If you already own a fluorescent shop light, use it. If you are buying new, buy LED.

Incandescent (skip it)

Standard incandescent and halogen bulbs are a poor choice for plants. They waste most of their energy as heat, can scorch nearby leaves, and produce little of the light plants use efficiently. Ignore any "grow bulb" that screws into a lamp and gets hot to the touch.

How Bright Does a Grow Light Need to Be?

Bright enough for the plant, and this varies more than most beginners realize. Light needs run on a scale.

Seedlings and greens want a lot. These are the reason most people buy a light, and they are hungry. A research study in Scientific Reports found lettuce grew best at a daily light integral around 11.5 moles per square meter per day, more than a winter window supplies. For seedlings, University of Minnesota Extension recommends bright light from a dedicated fixture, not a distant room lamp.

Houseplants want less. Low-light houseplants are content with far dimmer conditions, which is why they survive indoors without help. If you are adding a light only to keep a pothos alive in a dark apartment, a modest LED is plenty.

For shopping, do not get lost in marketing wattage claims. A "1,000 watt equivalent" number tells you little. Look instead for a full-spectrum LED made for plants, and prioritize getting the light close to the foliage, which matters more than raw power. Intensity drops off sharply with distance, so a modest light a few inches away beats a powerful one across the room.

How Close and How Long Should the Light Be On?

Distance and duration are where most beginners go wrong, and both are easy to fix.

Distance

Keep the light close, then raise it as plants grow. For seedlings just up, University of Illinois Extension recommends keeping fluorescent lights only 2 to 4 inches above the tops of the seedlings. LED fixtures run cooler and can sit a bit higher, but the principle holds: close is better. A light hung two feet above a tray of seedlings is why so many stretch and flop. As the plants grow taller, raise the fixture to keep that few-inches gap.

Duration

Give plants 14 to 16 hours of light per day, then darkness. According to University of Illinois Extension, a minimum of 12 hours of bright light is needed, with 14 to 16 hours ideal, followed by 8 hours of dark. Do not run lights 24 hours a day. Plants use the dark period for normal metabolism and build sturdier stems with a real night. A cheap outlet timer handles this automatically and is the single best few dollars you can spend on an indoor setup.

Does the Color of the Light Matter?

You may see grow lights sold as purple ("blurple") or as plain white, and marketing makes the color sound complicated. For a home gardener, it is not. According to University of Minnesota Extension, plants use light across the spectrum, and a full-spectrum light that looks white to your eye supplies everything they need. The purple fixtures combine red and blue diodes, which plants use heavily, but white full-spectrum LEDs include those same wavelengths along with the rest, and they have a real practical advantage: you can actually see your plants clearly, spot pests, and read plant labels under white light.

Blue light tends to encourage compact, leafy growth, which is exactly what seedlings and greens want, while red light supports flowering and fruiting. A quality full-spectrum white LED covers both, so you do not need to buy separate lights for different stages of a home garden. Unless you specifically want the purple aesthetic, choose white full-spectrum. It grows plants just as well and makes the whole setup pleasant to live with, which matters when the light sits on your kitchen counter through a foggy winter.

How Do You Choose a Grow Light Without Overspending?

You can spend $500 on an indoor garden system or $30 on a light that does the same job for a home gardener. Here is how to land on the low end sensibly.

Match the light to the space. For a single seed tray or a few pots of greens on a counter, one LED shop light (roughly two to four feet long) or a clip-on LED does the job. You do not need a tent, a fan, or a controller to grow lettuce and seedlings.

Buy full-spectrum LED. A full-spectrum or "daylight" LED covers everything a home gardener grows. Ignore fixtures that produce only purple light unless you specifically want that look, since white full-spectrum LEDs are just as effective and far easier to work and read under.

Add a timer. A basic outlet timer is essential and cheap. It runs the 14-to-16-hour schedule so you never have to remember.

Skip the extras. Reflectors, meters, and elaborate stands are nice but optional. A shelf, a chain to hang the fixture, and a timer will grow a great deal of food.

For a Santa Cruz gardener, a modest LED shop light over a tray of greens turns a foggy December counter into a small, reliable salad factory. That is the whole point: a grow light removes weather from the equation.

Frequently Asked Questions

Do I really need a grow light, or is a sunny window enough?

A sunny window is enough for microgreens, sprouts, and low-light houseplants, but not for seedlings, salad greens, or keeping herbs productive. According to University of Illinois Extension, a bright window delivers only 2,000 to 5,000 foot-candles versus 10,000 to 12,000 outdoors. In foggy Santa Cruz County, winter window light drops further, so a grow light is worth it for anyone starting seeds or growing greens indoors.

Are LED or fluorescent grow lights better?

LED grow lights are the better choice for new setups. According to Utah State University research, modern LEDs deliver roughly 2.5 to 3.0 micromoles per joule, two to three times the efficiency of T5 fluorescents at about 1.0 micromole per joule. LEDs also run cooler and last longer. Fluorescent lights still work well for seedlings and greens, so if you already own one, keep using it, but buy LED when purchasing new.

How far should a grow light be from my plants?

Keep it close. According to University of Illinois Extension, fluorescent lights should sit just 2 to 4 inches above the tops of seedlings. LEDs run cooler and can sit slightly higher, but the same principle applies, since light intensity drops sharply with distance. Raise the fixture as the plants grow to maintain that small gap. A light hung too far away is the top cause of weak, stretched seedlings.

How many hours a day should a grow light be on?

Run a grow light 14 to 16 hours per day, then give plants darkness. According to University of Illinois Extension, plants need a minimum of 12 hours of bright light, with 14 to 16 ideal, followed by about 8 hours of dark. Do not leave lights on 24 hours a day, because plants build stronger stems with a real night period. An inexpensive outlet timer runs this schedule automatically.

How much does it cost to run a grow light in California?

Very little for a home setup. A modern LED shop light draws roughly the power of a couple of standard bulbs, and according to University of Missouri Extension, LEDs are highly efficient at converting electricity to plant light. Running one LED fixture 14 to 16 hours a day over a seed tray or a few pots of greens adds a small amount to a monthly bill, far less than the value of the greens and seedlings it produces.

Can I use a regular LED bulb from the hardware store as a grow light?

A standard white LED bulb provides some usable light and can help a low-light houseplant survive, but it is not intense enough for seedlings or salad greens. For growing food indoors, use a full-spectrum LED fixture made for plants, which delivers the intensity those crops need. Regular household bulbs are best thought of as a small supplement for tough houseplants, not a real grow-light replacement.

Grow With Us

A good grow light opens up seed starting, salad greens, and year-round herbs indoors. To put it to work, pair it with the timing and plant picks in Starting Seeds Indoors in California and our Indoor Gardening in California guide. For seasonal reminders and free resources, join our email list at your garden toolkit.