## 1 Introduction  
Light drives photosynthesis in plants, helping them to build carbon-based materials, and further acts as an environmental signal; plants respond to the intensity, wavelength, duration and direction of light [1]. Light is the primary energy source for plants and the most important regulatory factor in the life cycle of a plant: it affects the seed germination, seedling establishment, transition to flowering, and morphogenesis [2; 3].  
Night interruption (NI) during short day (SD) seasons effectively accelerated the flowering of long day plants (LDPs) and allowed earlier marketing or seed production, and delayed the flowering of short day plants (SDPs) during long day (LD) seasons [4]. NI for 4 h has usually been applied to both SDPs and LDPs in commercial greenhouse production [5]. The NI using low-intensity light emitting diodes (LEDs) is supposed to slightly affect the net photosynthesis and ensure growth promotion in tomatoes [6]. NI has effectively accelerated the growth and development of herbaceous LDPs such as _Campanula carpatica_[7], _Coregpsis grandifforum_[8], and _Cyclamen persicum_[9] in SD seasons. By inducing vegetative growth, NI has also been used to prevent or delay the flowering of herbaceous short-day plants (SDPs) such as _Dahlia pinnata_[10] and _Dendranthema grandiflora_[11]. Low-intensity NI (3-5 umol\(\cdot\)m\({}^{-2}\)\(\cdot\)s\({}^{-1}\) PPFD) was used to effectively promote flowering of juvenile _Cymbidium aloifolium_ with increased growth rates [12].  
NI with red (R) light was shown to be the most effective in inhibiting flowering, and far-red (FR) light was able to revert this inhibitory effect in many cases [13]. As the FR light proportion increased (as the R:FR ratio decreased), flowering was increasingly promoted in _Pettunia hybrida_ (LDP) and inhibited in _Antirrhinum majus_ (SDP) [14]. The NI with FR light delayed flowering of the day neutral plant _Pelargonium \(\times\) hortorum_[15]. The NI with a combination of R and blue (B) lights (R:B = 1:1) more effectively promoted the flowering of _Cyclamen persicum_ (LDP) than NI with B, R, or FR light alone [16]. For _D. grandiflora_, NI with R light most effectively inhibited flowering, while NI with B or FR light wasn't very effective [17]. The NI with a combination of R and B lights (R:B = 1:1), and R light alone effectively inhibited the flowering of _D. grandiflora_[18]. In SDPs, low-intensity NI with B light, or B light supplemented with R and FR lights did not affect the flowering nor growth attributes [10; 19]. In a combined shifting treatment of B and W light, the NI ending with B light (NI-WB) induced flowering [19]. Thus, it is probable that the B light receptor can enhance floral-inducer activity, resulting in a higher energy requirement for the promotion of flowering [19].  
There has been little published on the effects of NI with LEDs on the morphogenesis and flowering, and especially the effects of NI on Crassulacean acid metabolism (CAM) plants. Furthermore, as LEDs have the benefits of easily controlled duration, intensity and quality, new practical applications of NI with LEDs for floricultural crop production are needed. In this study, the effects of the NIL quality and intensity on the morphogenesis and flowering of SDPs, kalanchoe (_Kalanchoe blossfeldiana_) 'Lipstick' and 'Spain', were examined.