## 1 Introduction  
Light signals regulate plant growth and development by sustaining environmental conditions [1]. To enhance growth and development, 24 h day/night plants develop an endogenous circadian clock [2]. This circadian clock is used to anticipate environmental changes and coordinate physiological and behavioral changes with environmental shifts [3]. Most flowering plants are severely dependent on light intensity patterns similar to their natural photoperiod conditions to trigger normal biological functions [4; 5; 6; 7]. However, photoperiodic conditions can be manipulated artificially to induce early flowering for commercial horticulture [8]. Manipulation of the photoperiod can also reduce production costs by reducing production times and improving the overall quality of the crop [9]. The photoperiod regulates growth and flowering in photoperiodic plants [10; 11; 12]. The use of artificial lighting at night (night interruption, NI) can regulate the flowering of photoperiodic species [13; 14]. The NI breaks a long dark period to deliver photoperiodic lighting and thereby create modified long day (LD) conditions [15]. It has been reported that _Cymbidium aloifolium_ photosynthesizes during 4 h NIs of photon fluence as low as 3-5 \(\upmu\)mol\(\cdot\)m\({}^{-2}\cdot\)s\({}^{-1}\) suggesting that the increased growth and earlier flowering times that occur in response to NI be attributed to an increase in net photosynthesis during this NI period [16]. Therefore, even NIs of low intensity are economical and effective means of controlling flowering in some species. The duration of the NI used in many studies [16; 17; 18; 19; 20; 21; 22; 23; 24; 25] investigating flowering control was \(\geq\)4 h. However, a short (15 min) interruption of the long-night phase effectively controlled flowering in chrysanthemum plants that were grown under B light during their photoperiod [24]. It is well known that the effect of light quality on flowering regulation varies among plant species [24]. Many long-day plants (LDPs) flower most rapidly when the artificial light they are exposed to contains far-red (Fr) wavelengths, particularly when the artificial light is applied at the end of the photoperiod [26; 27]. In SDPs, a night break with red (R) light effectively inhibits flowering, while flowering is promoted by subsequent exposure to Fr light [28]. This suggests that R/Fr reversible phytochromes may be involved in this response. The phytochrome photoreceptors mediate light quality perception, stem elongation, and flowering in photoperiodic plants [29]. Recent molecular and genetic investigations [30; 31] have revealed that phytochromes are essential for photoperiodic flowering in rice (a facultative SDP). Loss-of-function of all phytochrome rice genes (in the _se5_ mutant or _phyA phyB phyC_ triple mutant) resulted in a deficient photoperiodic response and early flowering in short-day (SD) and long-day (LD) [30; 31]. Flowering control by NIs presumably depends on the intensity, duration, and light quality of NI, as well as the plant species under consideration. Numerous papers have investigated the overall inhibitory effect of NIs on flowering when the NIs was timed to occur during the middle of the dark period. Although the effects of the duration and light quality of NIs were studied by [PERSON] _et al._[24] and [PERSON] [29], the effects of shifts in light quality of the NI have yet to be documented. Interestingly, [PERSON] _et al._[24] reported that in chrysanthemum grown with white light during photoperiod, flowering was observed under the SD interrupted in the middle of the dark period by a low intensity of blue (B) or far-red (Fr), while no flowering was observed under the same SD interrupted by red (R). Similar flowering responses were observed in our previous studies with chrysanthemum [32].