Growth of Lettuce ( Lactucasativa L.) Plant Under Red-Blue-White Light and Grow Light LEDs in Plant Factory System

— Indoor culture requires a variety of inputs to get maximum biomass. These inputs are the nutrients, temperature, humidity, and light which plants needed to photosynthesize. Different types of light have been studied and it is known that the same spectrum will give different responses by different plants. The purpose of this study was to find out the effect of red-blue-white light LED on lettuce growth compared to grow light LED as a control which commonly used in plant factory rooms. The red-blue-white light is arranged on a 100 cm long aluminum rod, mounted along the plant in a gully DFT hydroponic fed by 1000-2000 ppm nutrients of ABmix plus with a pH of 5.5-6.5. LED grow light provided the plant a significantly higher height of 16.30% compared to red-blue-white light, but was no different to the length of lettuce root. The number and the area of leaves in red-blue-white light were markedly higher at 16.67% and 33.78% respectively than grow light. In addition, the red-blue-white light increased the chlorophyll content, fresh weight, and dry weight of lettuce plants, by 25.00%, 101.49% and 58.13% consecutively. Therefore, these results suggested that the red-blue-white LED light provided a significant higher biomass than the grow light LED.


INTRODUCTION
Foodstuffs, especially vegetables such as lettuce, is very useful for the health of the body. The vegetable should be produced close to consumers (in the city) to reduce transportation costs, but because of land limitation in urban areas, a new system is needed to grow indoor crops by utilizing technology so that products are cleaner and healthier, which we call such system is plant factory.
Plant factory requires various inputs such as nutrient solutions and other growing factors such as temperature, humidity, and light energy. Light bulbs are needed for plants to photosynthesize to produce biomasa. There has been a lot of research about the type of light spectrum with its combination to provide optimal intensity in spurring plant growth. According to Senger (1982), the same type of light will give a different mophogenesis response depending on plant species. Yorio et al. (2001) found that fluorescent cool-white light (CWF) is best light at spurring lettuce growth compared to red, blue, and green rays and their combinations.In contrast, Kim et al. (2004) showed different data, namely that red-blue LED lights with a 24% green supplement at wavelengths of 500-600 nm was most spur the growth of lettuce plants compared to all other types of combinations including CWF light. CWF is a light commonly used as a control of lights that are broad spectrum approaching to solar rays. Furthermore, Shimizu

Materials and equipments
The materials used were the seedlings of the lettuce plant "Jonction RZ" in rock wool media, AB mix plus nutrient solution, pH lowering solution (nitric acid and phosphoric acid) and raw water. The equipments used were plant factory room, hydroponics system DFT (Deep Flow Technique), IoT System (which is able to show air humidity, room temperature, solution concentration, nutrient solution temperature, and able to regulate the pH of nutrient solution), white light LED polychromatic grow light (four spectrum peaks: λ = 450 nm, λ = 527-542 nm, λ = 608 nm, 54 watts), and red-blue-white combination LED lights with characteristic red light (λ=618 nm, 3 watts), blue (λ=452 nm, 2 watts), and white (λ=450 nm, λ=527-542 nm, λ=608 nm, 1 watt) ( Figure 1).

Seedling and planting
The seeds of Lactuca sativa L. cultivar "Jonction RZ" were immersed in rock wool with a size of 2 cm x 2 cm x 2 cm in a tray, then watered until saturated, covered with black plastic one night. Growing seedlings were then maintained and subjected to sunlight and watered every 2 days with a nutrient solution AB mix plus 500 ppm until two weeks old and transferred (transplanting) to gully in the DFT hydroponic system. The seedlingswere put into a net pot (basal diameter 3.5 cm, upper diameter 4.4 cm, height 5 cm) then placed in a gully hole with a distance of 20 cm.

LED light setup
The lights used in this experiment were grow light LED (Light Emitting Diode) lamp and a combined of red-bluewhite light LED. Grow light LED lamp is a series of LED bulb with a total of 54 watts. Red-blue-white light LED lamp is a series of repeated 3 red bulb, 1 blue bulb, and 1 white bulb. The lampswere set along a hydroponic gully that was a total length of 3.6 meters. The lamp was turned on for 18 hours and then turned off for 6 hours intermittently as a photoperiodic for the process of photosynthesis and respiration of plants.

Plant nutrient solution
The solution used to nourish plants was AB mix general vegetable containing macro and micro nutrients (Table 1) with the addition of Calcium nitrate (Ca(NO3)2) as much as 90 grams per literbased on method of Suryantiniet al.
(2019). with the SPAD Units (Special Products Analysis Division Units). Each plant was measured three leaves and each leaf was measured in three parts, namely at the tip, middle, and the basal of the leaf, then averaged. All data was analyzed with a t-test of 5% as the indipenden group.

III. RESULTS AND DISCUSSIONS
Plant growth was observed weekly since the plant was transplanted (0 mst, weeks after transplanting) to 4 mst. Other variables namely fresh weight, dry weight, leaf area, and amount of chlorophyll were observed during harvest at 4 mst.

Plant height and plant root length
Lettuce plants in plant factorywere treated led grow light and red-blue-white LEDs with photoperiodic 18 hours of on lights and 6 hours off alternately. Lettuce plants that were exposed to a LED grow light exhibited the plant height every week higher than plants on red-blue-white LED lights ( Table 2).The average height of plants in LED grow light was 15.7 cm,was markedly higher by 19.30% compared to plants illuminated by red-blue-white LED lights of13.16 cm. It was likely that plants experience mild ethiolation that occureddue to the intensity of grow light was low, allowing IAA growth hormone to be more active than the influence of red-blue-white light. Husen (2001) and Pacholczaket al. (2005) revealed that the presence of ethiolation will activate the IAA hormone that spured plant growth so that plants were higher, even the condition can also increase the number and length of roots on plant cuttings.
Although the LED grow light spectrum provided a more complete spectrum of between 420-750 nm with three peaks namely λ=450 nm, λ=527-542 nm, and λ=608 nm ( Figure 1) but its intensity was low at about 9000 lux for blue light and 8500 lux for the red spectrum compared to the red-blue-white light with 13,500 lux for the blue spectrum and 10,000 lux for the red spectrum. The appearance of the lettuce plant at the age of 4 mst (weeks after transplanting) was presented in Figure 3 below.

Number and areas of leaves
Lettuce leaves on red-blue-white LED lights every week were more leaves number than that exposed to led grow light ( Table 3). The average number of leaves on a red-blue-white light (13.16 sheets) was 16.67% higher than in LED grow light (11.28 sheets). The plants at the red-bluewhite light appear more lushes ( Figure 3 (Table 4). Much higher growth in these redblue-white LEDs than lettuce affected by grow light was due to the role of chlorophyll-a which absorbs blue light and chlorophyll-b absorbs red light which was of higher spectrum quality than the same spectrum in grow light rays (Figure 1). This was supported by Saeboet al. (1995) which states that red light can increase carbohydrate accumulation in the leaves by inhibiting the translocation of photosintat out of the leaves.
Blue and red light can increase biomass productivity, seed germination, plant stem growth (Parks et al., 2001), chlorophyll content when given green light supplements (Bianet al., 2018) in lettuce plants. Furthermore, Brown et al. (1995), found that red light (660 nm) requires a blue light supplement for chili plants to grow normally.  Plant chlorophyll was measured by SPAD Units (Special Products Analysis Division Units). The amount of chlorophyll contained in grow light LED and red-bluewhite LED differ markedly which were 18.2 SPAD and 22.8 SPAD, respectively. The amount of chlorophyll in leaves on red-blue-white LED lights was 25% higher than plants that exposed to grow light LED (Table 5). More chlorophyll in this treatment will support higher photosynthetic activity,thereafter the fresh weight and dry weight of the plant became greater. The fresh weight of the plantand the dry weight of the plant on the red-blue-white light treatment were greater significantly than the plants irradiated by grow light, respectively increased by 101.49% and58.13% (Tables 6 and 7). Thesewere supported by research conducted by Senger (1982) which stated that blue light spurs the formation of chlorophyll, the opening of stomata, and the formation of various enzymes involved in the process of photosynthesis. Blue light encourages the development of chloroplasts and increased in the amount of chlorophyll (Akoyunoglou and Anni, 1984) and when combined with red light (1:4) can markedly increased the amount of chlorophyll, fresh weight, and dry weight of spinach plants (Nguyen et al., 2021).  Significance by t-test 5%, tcount=1.5362, ttable=0.7176, z percentage of increase.

Conclusion
LED grow light exhibited the lettuce plant a significantly higher height of 16.30% compared to red-blue-white LED light. On the other hand, the number of leaf and leaf area in red-blue-white light LEDweremuch higher, which were 16.67% and 33.78% respectively compared to grow light LED. In addition, the red-blue-white light LED increased the content of chlorophyll, fresh weight, and dry weight of lettuce plants by 25.00%, 101.49%, and 58.13%, consecutively. Red-blue-and-white LED light provided a higher biomass than grow light LED.

Suggestion
More detailed studies should be done on the effect of redblue-white lights LED on the nutritional and phytochemical content of lettuce plants in plant factory.