Abstract: To address the critical issue of severe shading on lower canopy leaves and limited growth potential in leafy vegetable production, this study investigated the light interception characteristics of lettuce by measuring light and shade conditions on individual leaves at different growth stages. Based on the identified shading patterns, a Spatial-close lighting system (SCL) was developed. Light sources were arranged in close proximity around the lettuce canopy from both the top and lateral sides, enabling targeted supplemental lighting in shaded leaf regions and dynamic beam activation. The results showed that at 1～10 days after transplanting, lettuce had only 6 leaves, with small leaf area and uniform spatial distribution, resulting in minimal mutual shading effect, with a shading rate of merely 11.7%. At 11～20 days after transplanting, lettuce entered a rapid growth phase, during which 9 new leaves emerged, and the total leaf area increased sharply by 553.6%, leading to a substantial rise in the shading rate to 57.3%. During 21～25 days after transplanting, lettuce maintained rapid growth, with both shaded area and lighted area expanding simultaneously. Although 6 additional leaves were produced, they were concentrated at the top of the canopy and remained relatively small in size, so the shading rate only slightly increased to 61.8%. Furthermore, light distribution within the canopy was extremely uneven. At 25 days after transplanting, the average photosynthetic photon flux density (PPFD) of top layer leaves ranged from 160.7 to 179.5 μmol/(m²·s), whereas that of bottom layer leaves was merely 52.0 to 55.5 μmol/(m²·s). Based on these characteristics, the SCL was equipped with lower, middle, and upper LED modules installed at the central heights of major functional leaves at different growth stages (3, 8, and 13 cm above the cultivation panel, respectively), with dynamic power switching according to plant height. During the early growth stage (1～15 days after transplanting), lower full-spectrum LEDs with a red-to-blue ratio of 2.3∶1 and middle pure red LEDs were activated to promote root development in seedlings. In the rapid growth period (16～22 days after transplanting), middle and upper pure red LEDs were turned on to meet the vigorous photosynthetic and growth demands of the lettuce. Before harvest (23～25 days after transplanting), top full-spectrum LEDs with the same red-to-blue ratio of 2.3∶1 were additionally activated to further enhance the photosynthetic efficiency of lettuce. Cultivation experiments demonstrated that this energy-saving lighting system reduced the leaf shading rate by 39.6%, increased light intensity in the lower canopy by 43.3% and in the middle canopy by 11.0%. The aboveground fresh weight of lettuce increased by 23.1%, energy consumption per unit yield decreased by 65.8%, energy use efficiency improved by 193.0%, and total leaf area rose by 13.0%. The system effectively alleviated insufficient light exposure on shaded lettuce leaves, optimized light interception throughout the entire plant canopy, and created favorable light conditions for efficient and high-quality lettuce production in plant factories.