How Much Light is Required for Indoor Lettuce

Lettuce is one of the popular leafy greens that is grown all over the world. It is appreciated for its fresh texture, tasty flavor and rich vitamins. Moreover, lettuce is of small size and short production cycle. Therefore, lettuce is attractive to commercial growers as well as home growers. Traditional lettuce is grown in open-field, advanced technologies provide an opportunity for indoor lettuce growing. There are various technologies for indoor lettuce growing while vertical farming is one of the most profitable technology for commercial production. Since vertical farming is lack of sunlight, LED grow lights are used to supplement and mimic natural lighting for lettuce. Many growers are doubt for how much light they should supplement for indoor lettuce.

To figure out how much light is requirement for indoor lettuce, here are some considerations should be taken into account.

Do you need grow lights for indoor lettuce?

Generally speaking, lettuce is a full-sun and cool-weather vegetable. Appropriate lighting can promote germination and prompt growth speed. The key problem of indoor lettuce growing is the lack of natural light. Commercial lettuce production are carried out in buildings with vertical farming technology commonly, lettuces are unable to absorb enough sunlight. Tough other growing factors like temperature and humidity are controllable, lettuce cannot grow up without sunlight. Grow lights, however, are typically designed for indoor farming, providing optimal spectrum and controllable photoperiod. Therefore, grow light is irreducible for indoor lettuce.

What are the best grow lights for indoor lettuce?

Traditional grow lights including fluorescent and HPS/MH grow lights used to be adapted for indoor growing. With the development of LED grow lights, they are out of date. Except for the high energy consumption, they also have high possibility to damage the lettuce with their inevitable heat. In contrast, LED grow lights are proven to be long lasting, energy saving, and high efficient. Moreover, researches have shown that LED grow lights are more efficient to increase productivity than conventional grow lights.

Now, we are clear that LED grow lights are greater than others. But which LED grow light is optimal for indoor lettuce?

The optimal LED grow lights should provide sun-like supplemental light for lettuce, improving growth as well as achieving year-round production. Wavelength ranged from 400 nm to 700 nm is defined as Photosynthetically Active Radiation (PAR), which is beneficial for photosynthesis. As a result, LED grow lights with full spectrum are perfect for indoor lettuce. Here are two options: Horti-Sky and Horti-Green. Horti-Sky provides periods of reduced intensity, which allows regeneration of the photosynthetic apparatus and ensures better energy management. Horti-Green is perfect for leafy greens grown in vertical farms, being able to completely replace florescent T5 fixtures or HPS/MH lights.

How many hours should be supplemented for indoor lettuce?

The time of supplemental lighting for indoor lettuce is relative to the photoperiod. Photoperiod is the total time that plants are exposed to daylight during 24 hours. Natural lights are changed along with rolling on season, and plants react to the lengths of light exposure. Morphology of lettuce is effected by photoperiod. Shorter light cycle contributes round shape and higher planting density while longer light cycle allows better light capture modulating slender leaves. Lettuce needs at least 8 hours sunlight a day in common condition. But this photoperiod differentiates from cultivars, weather, and cultivated locations. Generally, recommended photoperiod of indoor lettuce ranges from 12 to 20 hours. Growers can adjust the photoperiod according the growing stage of lettuce. A photoperiod between 14 to 16 hours is ideal for germination. Once the seedlings emerge, reduce the photoperiod to about 12 hours.

To sum up, here is a table about the lighting recommendations for indoor lettuce. If you have any problems about supplemental light, or would like to tailor lighting spectrum for your plants, please feel free to contact us. Atop is ready to provide supplemental lighting solution at all times.