An experiment was conducted in controlled environment chambers to evaluate the effect of varying levels of blue light on vine growth and storage root yield of sweetpotato [ I p o m o e a batatas (L.) Lam.] when grown in nutrient film technique (NFT). Cuttings of'TU-82-155" sweetpotato were grown under 6, 11, 16, 22.5, and 26% blue light (320-496 nm) supplied by high intensity discharge metal halide and high pressure sodium lamps. Total fresh mass was greatest for plants grown under 22.5 or 26% , and lowest for plants under 11% blue light. Total plant dry mass and storage root yield, however, were similar among treatments. Harvest index (storage root dry mass/total plant dry mass) was highest for plants grown under 26% blue light. Plants grown under 26% blue light tended to have a higher growth rate. Both vine and internode length tended to decline as the percentage of blue photons increased. These results indicate that storage root yield was not adversely affected by exposure to blue light as high as 26%, and that the main effect of blue light was to cause a reduction in vine length.