Design parameters of flat-panel LED modules for plant lighting applications

Semispherical high-intensity light-emitting diodes (LEDS) mounted on a circuit board have been developed and examined for plant growth applications. This type of LED configuration, however, has problems such as relatively poor heat dissipation, difficulty of effecting high light uniformity, and high cost of assembly. Such problems may now be obviated through use of the recently developed flat-panel LED modules. In this study, the photosynthetic photon flux (PPF) levels and PPF distribution of 172 x 27 mm red flat-panel LED modules were determined. Results showed that: 1) the red flat-panel LED modules tested produced a mean PPF level of about 111 micromoles m-2 s-1 at a distance of 10 cm, which would be adequate for most micropropagated species grown photomixotrophically and reasonable for some micropropagated species grown photoautotrophically, both in terms of red wavelength; 2) the mean surface PPF of 419 micromoles m-2 s-1 for a single LED in a flat-panel module was about 47% greater than that for a single semispherical LED at about equal operational currents, owing primarily to the significantly larger reflectance area present in a flat-panel LED than that in a semispherical LED; 3) two flat-panel LED modules tested had about 80% of their illuminated areas having PPF values equal to or greater than half their maximum PPF levels, whereas the third module had a corresponding figure of about 67%; and 4) flat-panel LED modules exhibited very similar PPF distributions, underscoring the advantage of the LED flat-panel design over the manually assembled LED array in the ease of replicating light distributions.