Compare chlorophyll absorption spectra with the actual LED light sources used in your photosynthesis experiment. Toggle different light sources to understand why some colours drive photosynthesis better than others.
Why Blue LED works best: The 453nm peak overlaps almost perfectly with chlorophyll b's blue absorption peak (~453nm) and is close to chlorophyll a's (~430nm). Strong intensity at 409.74 mW/m².
Why Green LED is more effective than expected: The 519nm peak falls in the "green gap" where chlorophyll a and b absorb poorly, which would predict minimal photosynthesis. In practice, however, green light consistently drives more photosynthesis than the absorption overlap alone suggests. This is likely because green light penetrates deeper into the Chlorella cell suspension than blue or red — which are absorbed near the surface — allowing more cells to be reached. Accessory pigments (such as carotenoids) that absorb in this region may also contribute. The 166.41 mW/m² intensity is moderate, so the effect is real but not as strong as blue or red.
Why Red LED is moderate: The 634nm peak sits between chlorophyll b's red peak (~642nm) and chlorophyll a's red peak (~662nm) — not a perfect wavelength match for either, despite strong intensity at 413.34 mW/m².
Purple LED: Dual peaks at 453nm (blue, dominant) and 634nm (red, ~65% the height). The strongest source at 435.63 mW/m², simultaneously targeting chlorophyll b's blue absorption peak and the red absorption region of both pigments.
Yellow LED: Despite being perceived as "yellow" (dominant wavelength 573nm), the emission peak is actually at 634nm — squarely targeting chlorophyll b's red absorption peak (~642nm) and reasonably close to chlorophyll a's red peak (~662nm). Moderate intensity at 301.95 mW/m². Worth noting that students may find it counterintuitive that a "yellow" light box emits predominantly red wavelengths — the dominant wavelength (what the eye perceives) differs from the spectral emission peak.