Zenius Bliznikas

Quadrichromatic white solid-state lamp with digital feedback

White light with high color rendering indices can be produced by additive color mixing of emissions from several light-emitting diodes (LEDs) having different primary colors. White Versatile Solid-State Lamps (VSSLs) with variable color temperature, constant-chromaticity dimming, and efficiency/color-rendering trade-off can be developed using pulse-width modulation (PWM) driving technique. However, such lamps exhibit chromaticity shifts caused by different temperature and aging coefficients of the optical output for primary LEDs of different colors. To overcome this drawback, we developed a polychromatic white solid-state lamp with an internal digital feedback. The lamp features a quadrichromatic (red-amber-green-blue) design based on commercially available high-power LEDs. The design is optimized to achieve high values of the general color rendering index (69 to 79 points) in the color-temperature range of 2856 to 6504 K. A computer-controlled driving circuit contains a pulse-width modulator and a photodiode-based meter. The software performs periodical measurement of the radiant flux from primary LEDs of each color and adjusts the widths of the driving pulses. These VSSLs with feedback found application in phototherapy of seasonal affective disorder (SAD).

High-power LEDs for plant cultivation

We report on high-power solid-state lighting facility for cultivation of greenhouse vegetables and on the results of the study of control of photosynthetic activity and growth morphology of radish and lettuce imposed by variation of the spectral composition of illumination. Experimental lighting modules (useful area of 0.22 m2) were designed based on 4 types of high-power light-emitting diodes (LEDs) with emission peaked in red at the wavelengths of 660 nm and 640 nm (predominantly absorbed by chlorophyll a and b for photosynthesis, respectively), in blue at 455 nm (phototropic function), and in far-red at 735 nm (important for photomorphology). Morphological characteristics, chlorophyll and phytohormone concentrations in radish and lettuce grown in phytotron chambers under lighting with different spectral composition of the LED-based illuminator and under illumination by high pressure sodium lamps with an equivalent photosynthetic photon flux density were compared. A well-balanced solid-state lighting was found to enhance production of green mass and to ensure healthy morphogenesis of plants compared to those grown using conventional lighting. We observed that the plant morphology and concentrations of morphologically active phytohormones is strongly affected by the spectral composition of light in the red region. Commercial application of the LED-based illumination for large-scale plant cultivation is discussed. This technology is favorable from the point of view of energy consumption, controllable growth, and food safety but is hindered by high cost of the LEDs. Large scale manufacturing of high-power red AlInGaP-based LEDs emitting at 650 nm and a further decrease of the photon price for the LEDs emitting in the vicinity of the absorption peak of chlorophylls have to be achieved to promote horticulture applications.

OPONENTINĖS FUNKCIJOS IR SPALVŲ SKIRIAMOJI GEBA

The paper deals with the problem of a construction of opponent functions, which stem from the linear summation of three receptor (R, G, B) signals. It is considered two stages model: stage of the receptors and stage of the opponent cells. Each stage has the own intrinsic independent generators of noise. The colour is determined by the point in three-dimensional space with coordinates {x i }, (i=l, 2, 3), where x i is value of the output signals of the opponent cells. Let V be the volume of “colour body” and be the volume of sphere, where an end of a colour vector is located with a given probability P 0 . Then a ratio V/s characterizes a colour discriminability: the greater ratio V/s the greater discriminability of the system. It is looking for such transformation of receptor signals into opponent those (i.e. searching a linear operator A), that the ratio V/s would be maximal. The properties of the proposed model were investigated. They fit well to the properties obtained in traditional psychophysical experiments: opponent colour functions, hue coefficients, wavelength and saturation discrimination, achromatic channel sensitivity, non-additivity of brightness. This led to conclusion that the possible role of the colour opponency is ensuring optimal colour discriminability in human vision.