Indoor Light for Lettuce & Leafy Greens

Indoor Light for Lettuce & Leafy Greens

Jul 21, 2021Get UrbanLeaf Admin

Leafy greens tend to be short-lived crops in nature but when grown in a controlled environment, like your home, they can be harvestable for a long time. The game is to not let them think it’s summer (when it gets too hot or the days get too long, they end their life cycle). Their fast-growing nature combined with ample and consistent light results in impressive, regular harvests for you. In this blog, we’ll cover their lighting and temperature needs and how to get the most out of your plants. 

Lettuce and Other Leafy Greens Light Requirements

Outdoors, leafy greens thrive in the shorter days of spring – the short bright day gives them enough energy to grow and the longer nights keep them focused on growing leaves. When they sense shorter summer nights, their focus switches to making seeds before winter. 

Indoors it’s our goal to have the longest, productive harvest possible, so we’ll provide them with enough light to grow well, and enough darkness to keep them in their first growth stage as long as possible. Below is a chart of the amount of direct sun that popular leafy greens need. The last column is if they need to spend more than half the day in the dark to stay “vegetative” longer. Scroll further down and you’ll see other lettuce light requirements.

Do I have enough sunlight to grow leafy greens?

Because leafy growth does best in the lower light, you might just be lucky enough to have enough natural light to grow these plants without any problem. It’s a great way to get started (especially in the spring or fall) but ultimately we prefer using grow lights because they can grow the plants faster and for longer. Your indoor light conditions change day-to-day and with the seasons – so if you want to try it without a grow light, check out our exercises to understand your natural light environment.

How much light does Lettuce need per day: Indirect vs. Direct light

As shown in the table, most leafy greens grow well with at least 5 hours of direct light per day. This means 5+ hours of sunlight hitting the plant leaves is recommended for growing lettuce and other leafy greens. These plants can also grow if you happen to have a very bright window, but the sun only shines through for a few hours.

Season & Window Direction

South facing windows are typically the brightest, and thus your best chance for growing indoors with just natural light, though you will need to understand some seasonal shifts. In the fall and spring, bright, unobstructed southern windows work well for growing lettuce & leafy greens – the bright short days are what they need to thrive. In the summer, southern windows can get too hot (over 80F) and they’ll be exposed to light for >12 hours which will cause them to end their life cycle early  – so consider growing your greens in cooler east facing windows. In the winter, your southern window is still your best bet, but the weaker sunlight might need to be combined with a grow light or some of these hacks to increase your natural light [coming soon].

Reading your plants

The ultimate test of your natural light will be your plant’s growth. You can tell very early if you are way off the mark – you’ll notice the seedlings stretching and becoming spindly. Beyond that it’s a bit harder to tell where you are in the “adequate to optimal” range, but if your growth is way slower than is listed on the seed packet, the plant would likely do better with more light. If you are unsure, we recommend trying radishes as a quick-growing, easy to read diagnostic [coming soon].

Setting Up A Grow Light For Year-Round, Fast-Growing Greens

Grow lights can be a little intimidating – but they really shouldn’t be! There is alot of marketing noise to cut through, but at the end of the day a well-designed grow light provides a 1:1 replacement for sunlight, looks nice in your home, and pays for itself. Plants love the consistency of grow lights, which helps your little space be as productive as possible.

We consider the grow light an essential tool of indoor gardening, and with leafy greens relatively low light needs, it’s easy to put them in their “optimal” range with lights. The instructions below give practical instructions for our grow light, but if you’d like to have a deeper general understanding, check out the introduction to our grow light series.

Using a Grow Light Bar

Note: This section references Urban Leaf’s upcoming Grow Light Bar, due Spring 2021.

We have several grow light buying guides [coming soon] (for screw-inclip onbars, and free standing options) but if you’re using our Grow Light Bar then it’s quite simple to set up a leafy green grow area. The grow bar mimics a 6” x 12” patch of direct sunlight when placed 6 inches above a plant, so just match the timer to the plant’s “direct sunlight” hours.

Considerations with other grow lights for lettuce

Grow lights come in all types of sizes, shapes, and technologies. For herbs, high-powered lights (ie. Metal Halide or High-Pressure Sodium) can put out too much way too much heat. LED’s can be great, but there is a wide range of light quality. Fluorescent grow lights run cooler and are perfectly suitable to grow herb, lettuce and greens. We also recommend these grow lights for lettuce and greens. If you are interested in setting up a more complicated grow light system, we recommend understanding Daily Light Integral,  correct setup and placement, and how many hours a day to leave them on 

Best Grow Lights for Lettuce

According to, here are the best grow lights for lettuce.

Best Grow Lights For Lettuce: Comparison Table


LED Grow Lights






≥ 100,000 hours


Famurs 2000W LED Grow Light


≥ 10,000 hours




≥ 100,000 hours


BestVA 3000W LED Grow Light


≥ 100,000 hours


AntLux 50W 4Ft Growing Lamp


≥ 50,000


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Comments (2)
  • Very good lesson, thank you very much

    LAkmal Nimalarathne
  • Very informative—-I have been growing lettuce all wrong (too much light) and my crop show it!! I did not understand the importance of darkness!,

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