Changes in leaf variegation and coloration of english ivy and polka dot plant under various indoor light intensities

Variegated foliage plants are often used in interiorscaping in low light environments. The changes in leaf morphology and coloration of two variegated foliage plants, english ivy (Hedera helix 'Golden Ingot') and polka dot plant (Hypoestes phyllostachya), under various light intensities [photosynthetic photon flux (PPF) at 2.7, 6.75, 13.5, 67.5, and 135 μmol m^-2 s^-1] were investigated to elucidate their optimum indoor light environment. Digital image analysis was used to quantify the changes in variegation area and color in CIELAB color space. The changes in leaf morphology (thickness, length:width) and coloration were different between the two species. In general, growth of both species increased with increasing PPF. English ivy showed no significant changes in leaf variegation under different PPF. Under low PPF (≤13.5 μmol m^-2 s^-1), newly developed leaves of polka dot plant had reduced leaf variegation (44%, 72%, and 85% variegation loss under 13.5, 6.75, and 2.7 μmol m^-2 s^-1, respectively). Anthocyanin content in leaves of polka dot plant also decreased with decreasing PPF, which reduced plants' aesthetic quality. English ivy leaves under high PPF (≥67.5 μmol m^-2 s^-1) displayed high brightness (L*) and yellowish green color (hue angle < 108°), which diminished its aesthetic value. Smaller leaf size and narrower shape of polka dot plant leaves under high PPF (≥67.5 μmol m^-2 s^-1) also diminished its aesthetic value. Overall, english ivy performed well in a PPF range from 2.7 to 13.5 μmol m^-2 s^-1, and polka dot plant required a PPF of at least 13.5 μmol m^-2 s^-1 to maintain its redpurple variegation in the indoor environment.