Increasingly, vegetables are being efficiently grown using soilless techniques such as hydroponics. Hydroponic systems are favored for their ability to improve water and nutrient use efficiency and crop yields, and have the added benefit of allowing growers to use fewer chemical fertilizers. Researchers in China and United Kingdom studied the effects of LED light combinations on lettuce grown in hydroponic systems to determine whether the treatments could reduce nitrate accumulation, and to find out what effect the treatments might have on phytochemical levels.

Scientists have developed a method to make lettuce darker and healthier using ultraviolet (UV) light-emitting diodes (LEDs). Steven Britz of the U.S. Department of Agriculture and his colleagues used low-power LEDs that exposed lettuce to ultraviolet B (UVB) light for 43 hours. The lettuce was noticeably darker than plants not exposed to the UVB. They have not quantified this effect, but the lettuce darkening increased with the intensity of the light. Darker lettuce, like spinach, is known to be more nutrient dense than its lighter counterparts, such as iceberg.