Night-break has an inhibitory effect on flowering in short-day (SD) plants and is widely used in chrysanthemum -Chrysanthemum morifolium Ramat.) production for flowering regulation. Although LED lamps are a new light source in agriculture, there have been few studies on chrysanthemums under LED light cultures. One incandescent (INC) lamp and four monochromatic LED lamps, with peak emissions at 630 nm, 660 nm, 690 nm, 735 nm, and 660+735 nm, respectively, were used as night-break light sources in chrysanthemum cultivation. Shoot elongation was enhanced significantly in both 'Jimba' and 'Iwa no hakusen' under treatments using light sources that emitted far-red (FR) light (LED-735, LED- 660+735, and the INC lamp) compared with SD, LED-630, and LED-660 treatments. Photon flux density (PFD) in the range 700-799 nm was significantly related to the internode length. As shoot elongation under FR light increased internode elongation but not node number, it is probable that internode elongation was caused by gibberellin biosynthesis induced by FR light. Shoot lengths under the LED-630 and LED-660 light regimes, which only emitted red light, were not significantly different from those under control conditions. There was no significant relationship between internode length and Pfr/Ptotal, or the R/FR ratio.