1. Introduction
2. Materials and Methods
2.1 Plant Material and Growth Conditions
Uniform mung bean seeds (Vigna radiata cv. Berke) were surface-sterilized (1% NaOCl for 5 min) and imbibed in distilled water for 4 h. Twenty seeds per replicate (n=5) were placed on 1% agar in Petri dishes (90 mm diameter). Dishes were positioned in climate-controlled chambers (22 ± 1°C, 70% RH, 16/8 h photoperiod).
2.2 Light Treatments
LED panels (Philips GreenPower, 100 μmol m⁻² s⁻¹ PPFD at canopy level) delivered monochromatic treatments: red (peak 660 nm, FWHM 20 nm), blue (450 nm, FWHM 25 nm), green (525 nm, FWHM 22 nm), white (broad 400-700 nm), and dark control. Spectral irradiance was measured with a spectrometer (Apogee PS-300). Daily PPFD was verified to ensure consistency.
2.3 Measurements and Statistics
Sprouting was assessed daily: germination % (radicle >2 mm), time to 50% germination (T50), hypocotyl length (day 7), and fresh weight. Data were analyzed using one-way ANOVA followed by Tukey’s HSD (p < 0.05) in R v4.2.1. Results are mean ± SE.
3. Results
Red light treatment yielded the highest germination rate (92.5 ± 2.1%) after 5 days, significantly surpassing blue (78.3 ± 3.4%), white (85.6 ± 2.8%), green (45.7 ± 4.2%), and dark (32.1 ± 5.0%) (F_{4,20} = 147.2, p < 0.001; Figure 2). T50 was shortest under red (2.8 ± 0.2 days) versus green (5.1 ± 0.4 days).
Hypocotyl elongation on day 7 was greatest under red (18.4 ± 1.2 mm) and blue (15.7 ± 1.0 mm), with green showing etiolation-like shortness (6.2 ± 0.8 mm). Fresh weight correlated positively with germination vigor (r=0.92, p < 0.01). Spectral analysis confirmed phytochrome-mediated responses, as far-red supplementation to red reduced sprouting by 25% (data not shown).
4. Discussion
The superior sprouting under red LED light aligns with phytochrome Pfr activation, which derepresses cell wall-loosening enzymes and promotes radicle protrusion (Quint et al., 2011). Blue light, while activating cryptochromes for stomatal opening and chlorophyll synthesis, induces hypocotyl shortening via CONSTITUTIVE PHOTOMORPHOGENIC1 (HY5) pathways, explaining moderate performance (Pedmale et al., 2016). Green light’s poor efficacy may stem from weaker absorption by chlorophyll and antagonistic interactions with red/far-red balance (Zhen & Bugbee, 2020).
These results have profound technological implications for CEA. Red-dominant LEDs could accelerate sprouting in automated systems, reducing cycle times by 20-30% and enhancing throughput in vertical farms (Beacham et al., 2019). Integrating spectrally tunable LEDs with IoT sensors enables dynamic lighting, optimizing energy use—critical as lighting accounts for 40% of CEA operational costs (Kozai et al., 2019).
Limitations include species-specificity; future work should test monocots like wheat. Nonetheless, this study provides empirical data for LED technology deployment, bridging photobiology and agritech innovation.
Video 1: Experimental setup and time-lapse of mung bean sprouting under monochromatic LEDs.
Comparison Table: Sprouting Metrics by Light Color
| Light Color | Germination % (Day 5) | T50 (Days) | Hypocotyl Length (mm, Day 7) | Fresh Weight (mg/seedling) |
|---|---|---|---|---|
| Red (660 nm) | 92.5 ± 2.1 | 2.8 ± 0.2 | 18.4 ± 1.2 | 45.2 ± 3.1 |
| Blue (450 nm) | 78.3 ± 3.4 | 3.5 ± 0.3 | 15.7 ± 1.0 | 38.9 ± 2.8 |
| Green (525 nm) | 45.7 ± 4.2 | 5.1 ± 0.4 | 6.2 ± 0.8 | 22.1 ± 2.4 |
| White | 85.6 ± 2.8 | 3.2 ± 0.2 | 16.8 ± 1.1 | 41.3 ± 2.9 |
| Dark Control | 32.1 ± 5.0 | 6.4 ± 0.5 | 4.5 ± 0.6 | 15.7 ± 1.8 |
Note: Values are means ± SE (n=5). Different letters indicate significant differences (p < 0.05).
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