Spectral characteristics of sole-source lighting treatments.

Six sole-source lighting treatments were delivered from mint white (MW), red (R), blue (B), and green (G) light-emitting diodes (LEDs) at total photosynthetic photon flux density (PPFD) = 160 μmol∙m−2∙s−1. The subscript values after each LED type indicate the percentages of the total PPFD delivered from each LED type.</p

Influence of percentage of green light on shoot fresh mass, dry mass, and moisture content of lettuce ‘Cherokee’ and tomato ‘Bamborange’ with (+) and without (-) far-red light.

See Fig 1 and Table 1 for information on the lighting treatments. Each data point represents the mean and standard deviation of two replications with 10 subsamples (plants) per replication and species (n = 20). Regression equations, r2 values, and P values are presented when statistically significant (solid line) but not when non-significant (dashed line).</p

Plant height, total leaf area, fresh and dry weight for four species at the transplant stage (A-O).

Begonia ‘Olympia Red’, geranium ‘Pinto Premium Deep Rose’, snapdragon ‘Liberty Classic Yellow’, and petunia ‘Wave Blue’ seedlings were grown for 34 d, 25 d, 24 d and 19 d, respectively, under six sole-source lighting treatments delivered from mint white (MW), red (R), blue (B), and green (G) light-emitting diodes at a total photosynthetic photon flux density (PPFD) = 160 μmol∙m−2∙s−1. The values after each LED type represent their percentages of the total PPFD. Means with different letters are significantly different by Tukey’s honestly significant difference test (P < 0.05) and lack of mean separation indicates nonsignificance. Error bars indicate standard errors of 20 observational units [two replications with 10 subsamples (plants) per replication per species].</p

Results from two-factor analysis of variance.

P values are listed for the effects of green (G, 500–600 nm) light, far-red (FR, 700–800 nm) light, or their interaction on plant growth parameters of lettuce and tomato.</p

The spectra of nine lighting treatments.

Lighting treatments consisted of blue (B, 400–500 nm), green (G, 500–600 nm), red (R, 600–700 nm), and far-red (FR, 700–800 nm) light delivered by light-emitting diodes. The value that follows each waveband indicates its photon flux density in μmol∙m−2∙s−1.</p

Raw data for Fig 1.

The spectra of nine emulated lighting treatments consisting of blue (B, 400–500 nm), green (G, 500–600 nm), red (R, 600–700 nm), and far-red (FR, 700–800 nm) light delivered by light-emitting diodes. (XLSX)</p

Influence of percentage of green light on leaf number and SPAD index of lettuce ‘Cherokee’ and tomato ‘Bamborange’ with (+) and without (-) far-red light.

See Fig 1 and Table 1 for information on the lighting treatments. Each data point represents the mean and standard deviation of two replications with 10 subsamples (plants) per replication and species (n = 20). Regression equations, r2 values, and P values are presented when statistically significant (solid line) but not when non-significant (dashed line).</p

Spectral distribution of sole-source lighting treatments.

Six sole-source lighting treatments were delivered from mint white (MW), red (R), blue (B), and green (G) light-emitting diodes (LEDs) at total photosynthetic photon flux density (PPFD) = 160 μmol∙m−2∙s−1. The subscript values after each LED type indicate the percentages of the total PPFD delivered from each LED type.</p

Raw data for Table 2 & Figs 2–4.

Although green (G, 500 to 600 nm) and far-red (FR, 700 to 800 nm) light play important roles in regulating plant growth and development, they are often considered less useful at stimulating photosynthesis than red (R, 600 to 700 nm) and blue (B, 400 to 500 nm) light. Based on this perception, approaches to modifying the transmission of greenhouse glazing materials include (1) conversion of G photons from sunlight into R photons and (2) exclusion of the near-infrared (>700 nm) fraction of sunlight. We evaluated these approaches using simulated scenarios with light-emitting diodes to determine how partial and complete substitution of G with R light and exclusion of FR light affected the growth of lettuce and tomato grown indoors. The substitution of G with R light had little or no effect on fresh and dry mass of tomato. However, with the presence of FR light, fresh and dry mass of lettuce increased by 22–26% as G light was increasingly substituted with R light. In tomato, excluding FR inhibited plant height, leaf area, and dry mass by 60–71%, 10–37%, and 20–44%, respectively. Similarly, in lettuce, excluding FR inhibited plant diameter, leaf length, and dry mass by 15–23%, 23–33%, or 28–48%, respectively. We conclude that the spectral conversion of G-to-R photons can promote plant growth in at least some crop species, such as lettuce, while the exclusion of FR decreases crop growth and yield.</div

1931 CIE (x, y) chromaticity coordinates, correlated color temperature (CCT), and color rendering index (CRI) of sole-source lighting treatments.

Six sole-source lighting treatments were delivered from mint white (MW), red (R), blue (B), and green (G) light-emitting diodes (LEDs) at a total photosynthetic photon flux density (PPFD) = 160 μmol∙m−2∙s−1. The subscript values after each LED type indicate the percentages of the total PPFD delivered from each LED type. CIE coordinates (x, y) for each sole-source lighting treatment (symbols) with the black-body curve (black solid line) and CCT values are presented.</p