In the present study, the functions of vascular connections (graft unions) in the grafted tomato seedlings (Solanum lycopersicum cv. Super Doterang grafted on cv. B-Blocking) has been monitored with some indicating factors such as transpiration, water uptake rate, sugar content, flower dye distributions between scion and rootstock, and hardness of the grafted unions. In addition, various light qualities have been tested to evaluate the effects on functions of vascular connections particularly on xylem and phloem. Our results depicted that light had a positive effect on the development of grafted unions as well as their functions. The functions of stomata and vascular connections developed approximately 50% particularly in the first five days function monitoring. Moreover, the reduction of sugar content in the scion parts was inhibited instead of the dark condition. The use of the pure red and blue light sources in the acclimating chamber showed difficulties to keep the water balance of the grafted seedlings and the sudden abiotic stress condition (high light intensity) was observed. At day 4 after grafting, the gap between transpirational water loss and water uptake in the FL (fluorescent light) and LEDW1R2B1 (light emitting diode white/red/blue) supplying treatment was found to be the smallest, the gap. Our results therefore indicated that light sources from light emitting diodes (LEDs) combined with wave lengths might be beneficial contributions for developing vascular bundles and stomatal behaviors of the grafted seedlings during the wound healing period. © 2016 Elsevier B.V.