Plants use light energy to drive photosynthesis, the process by which they convert carbon dioxide and water into glucose and oxygen. Different wavelengths of light provide different amounts of energy, and plants absorb some wavelengths more efficiently than others. Researchers conducted two experiments to investigate how LED lights of different wavelengths affect the growth of basil seedlings.
Experiment 1
Sixty basil seedlings of identical age (14 days old) were divided equally into 6 groups. Each group was placed in an identical growth chamber equipped with LED lights that emitted a single wavelength of light. The wavelengths tested were: 450 nm (blue), 525 nm (green), 625 nm (red), 660 nm (deep red), 730 nm (far-red), and a control group receiving white LED light containing all wavelengths.
All chambers maintained the same temperature (22°C), humidity (65%), and watering schedule (50 mL every 48 hours). The LED lights operated for 16 hours per day at identical intensity (150 μmol/m²/s). After 21 days, the researchers measured the height (in cm) and dry mass (in grams) of each plant.
Figure 1 shows the experimental apparatus used for each treatment group.
Figure 2 shows the average plant height after 21 days for each wavelength treatment.
Experiment 2
The researchers hypothesized that combining red and blue light might be more effective than either wavelength alone. They set up 4 new growth chambers with the following LED configurations:
All other conditions remained the same as in Experiment 1. After 21 days, average plant height and dry mass were measured.
Table 1 shows the results of Experiment 2.
| Chamber | Light Ratio | Avg Height (cm) | Avg Dry Mass (g) |
|---|---|---|---|
| A | 100% Red | 17.6 | 2.1 |
| B | 100% Blue | 15.0 | 2.8 |
| C | 75% Red / 25% Blue | 18.9 | 3.4 |
| D | 50% Red / 50% Blue | 17.2 | 3.6 |