Asparagus (Asparagus officinalis L.) spears were treated with white (color temperature 4,500 k), blue (peak 450 nm), and red (peak 660 nm) light-emitting diodes (LEDs) at a photosynthetic photon flux density (PPFD) of $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for 12 h, and UV-B (280 nm) at 0.5 kJ or 1.0 kJ to determine the effect on agronomic characteristics, antioxidant phytochemicals, and antioxidant activity. The fresh weight, length, and width of spears were not affected by light quality treatments. The free sugars and chlorophyll contents were increased by 9 and 41%, respectively in the UV-0.5 kJ treatments. Among the antioxidant phytochemicals (vitamin C, total phenol, rutin, and total flavonoid), vitamin C was most greatly affected by the light treatments. Vitamin C content was significantly increased in asparagus spears subjected to the white (114%), red (137%), and UV-0.5 kJ(127%) treatments compared to the control. By contrast, rutin, total phenol, and total flavonoid content were increased only in samples subjected to the red and UV-0.5 kJ treatment. Furthermore, antioxidant activity, as measured by DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, increased in white, red, and UV-0.5 kJ treatments by about 43, 41, and 43%, respectively, compared to the control. These results suggest that postharvest treatment of asparagus spears with red light at $200{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for 12 h or with UV-B (280 nm) at 0.5 kJ could enhance the functional quality of the asparagus spears by increasing the content of phytochemicals like vitamin C, rutin, total phenolics, and total flavonoids.