Intermittent Light Pulses Research Articles

Spectral sensitivity of circadian phase resetting, melatonin suppression and acute alerting effects of intermittent light exposure

Intermittent light (IML) pulses are more efficient per minute of exposure than continuous exposure in resetting the phase of the human circadian pacemaker. We assessed the spectral sensitivity in phase resetting, melatonin suppression and alertness induced by IML pulses. Twelve healthy young adults (6 females; mean age ± SD = 25.4 ± 3.6 years) were exposed to six monochromatic light pulses (2.8 × 1013 photons/cm2/s) over a 6.5 h window during the biological night. Six participants (3F) received 6 × 15-minute 460 nm (blue) pulses and six participants received 6 × 2-minute 555 nm (green) light pulses. Results were compared to historical data in 16 individuals who received continuous 460 nm (n = 8) or 555 nm (n = 8) light exposure using an identical protocol. As expected, long duration continuous 460 nm light exposure induced the largest total phase delay shifts, but intermittent 555 nm light induced the largest phase delay shifts per minute of the photic stimulus. Melatonin suppression was significantly higher under continuous light exposure compared to intermittent exposure patterns, and for 460 nm versus 555 nm exposure (under both light patterns). These data extend prior work showing a non-linear relationship between light exposure duration and phase resetting responses and illustrate the potential role of light wavelength, and therefore photoreceptor recruitment, in mediating these responses.

Light exposure time and light quality on seed germination of Vellozia species (Velloziaceae) from Brazilian campo rupestre

Species of Vellozia (Velloziaceae) inhabit open environments and produce small seeds with varying light-mediated germination requirements as a function of temperature. However, little is known about light quality and exposure time required for their germination. We aim to determine the germination responses of Vellozia species in relation to time and light quality. Seeds fully imbibed in the dark at 25°C were exposed to single light pulses, or pulses interrupted by dark periods (intermittent) for five consecutive days, or five different R:FR (red:far-red light) ratios. Control treatment seeds were maintained in constant light or darkness, or under 12-h photoperiod. The light time necessary to reach maximum germinability varied from two hours (Vellozia glauca) to 84h (V. albiflora); V. lilacina seeds did not germinate even after 96h of continuous exposure to light, while most species required more than 24h of light to reach maximum germination. The least time necessary to obtain 50% germination (t50) was 1h (V. glauca), while the maximum time was 103.8h (V. lilacina). The t50 for intermittent light was 10min (V. glauca) and the maximum time was 8h (V. glandulifera). Vellozia lilacina and V. albiflora did not attain maximum germinability after 8h of exposure to light during five consecutive days, demonstrating that intermittent light pulses are more efficient than continuous pulses for germination. Vellozia pusilla and V. albiflora presented maximum germination only at the greatest R:FR ratio (0.77), while V. caruncularis and V. glauca reached maximum germinability at the lowest R:FR ratios (0.02 and 0.08 respectively). The seeds of Vellozia spp. required different periods of light exposure and different R:FR ratios to reach maximum germinability, demonstrating a convergence between the time of light and the R:FR ratio. However, we were unable to find a germination pattern for the genus.

Optimizing LED lighting for space plant growth unit: Joint effects of photon flux density, red to white ratios and intermittent light pulses

The aim of this work were to choose a quantitative optimality criterion for estimating the quality of plant LED lighting regimes inside space greenhouses and to construct regression models of crop productivity and the optimality criterion depending on the level of photosynthetic photon flux density (PPFD), the proportion of the red component in the light spectrum and the duration of the duty cycle (Chinese cabbage Brassica сhinensis L. as an example). The properties of the obtained models were described in the context of predicting crop dry weight and the optimality criterion behavior when varying plant lighting parameters. Results of the fractional 3-factor experiment demonstrated the share of the PPFD level participation in the crop dry weight accumulation was 84.4% at almost any combination of other lighting parameters, but when PPFD value increased up to 500µmol m−2s−1 the pulse light and supplemental light from red LEDs could additionally increase crop productivity. Analysis of the optimality criterion response to variation of lighting parameters showed that the maximum coordinates were the following: PPFD = 500µmol m−2s−1, about 70%-proportion of the red component of the light spectrum (PPFDLEDred/PPFDLEDwhite = 1.5) and the duty cycle with a period of 501µs. Thus, LED crop lighting with these parameters was optimal for achieving high crop productivity and for efficient use of energy in the given range of lighting parameter values.

Kinematic Analysis of Drosophila Larval Locomotion in Response to Intermittent Light Pulses

We report a quantitative analysis of the modulation of locomotion by light in the Drosophila larva. The photobehavior of wild type larvae and of larvae carrying mutations altering various aspects of locomotion was evaluated in an assay that exposes individual animals to intermittent pulses of dark and light (ON/OFF assay). The application of the Dynamic Image Analysis System for the analysis of larval movement in the ON/OFF assay allowed a detailed description of the behavioral repertoire underlying the modulation of larval motion by light. We established that the larval response to light is characterized by decreased frequency of peristaltic contractions in addition to increased direction change and pausing. Moreover, using various mutant strains we show that this approach allows the detection of a response to light in mutant larvae whose locomotion is severely reduced and uncoordinated, mutants that would otherwise have been considered non-responders in this assay.

Regulation by light and metabolites of ferredoxin-dependent glutamate synthase in maize.

The regulation of Fd-glutamate synthase (Fd-GOGAT, EC 1.4.1.7) and NADH-glutamate synthase (NADH-GOGAT, EC 1.4.1.14) was investigated in maize (Zea mays L. cv. DEA) (1) during development starting from 7- to 11-day-old seedlings, (2) by treatment of 7-day-old etiolated leaves with intermittent light pulses to activate (red) and inactivate (far-red) phytochromes and (3) in 7-day-old green leaves grown under 16-h light/8-h dark cycles. Fd-GOGAT mRNA accumulated 4-fold, and the enzyme polypeptide (3-fold) and activity (3-fold) also increased in leaf cells, while NADH-GOGAT activity remained constantly low. Leaf-specific induction of Fd-GOGAT mRNA (3-fold) occurred in etiolated leaves by low fluence red light, and far-red light reversibly repressed the mRNA accumulation. Red/far-red reversible induction also occurred for Fd-GOGAT polypeptide (2-fold) and activity (2-fold), implicating the phytochrome-dependent induction of Fd-GOGAT. In contrast, NADH-GOGAT activity remained constant, irrespective of red/far-red light treatments. Fd-GOGAT showed diurnal changes under light/dark cycles with the maximum early in the morning and the minimum in the afternoon at the levels of mRNA, enzyme polypeptide and activity. Gln diurnally changed in parallel with Fd-GOGAT mRNA. The induction of Fd-GOGAT provides evidence that light and metabolites are the major signal for the Gln and Glu formation in maize leaf cells.

Effects of viscosity on phototactic movement and period of cell rotation in Cryptomonas sp.

The swimming speed, the period of cell rotation, and the critical dark period between intermittent light pulses in the positive phototactic response of Cryptomonas sp. strain IAM CR–1 were measured in the presence of methyl cellulose, which slows down the cell movement by raising the viscosity of the medium. The cell rotated once while it swam one pitch of the helical path, irrespective of the rotational period. The period of helical movement (the rotational period) was 0.65 s and 0.45 s in the presence and absence of 4.5 g/liter methyl cellulose, respectively. The phototactic response to repeated pulses of light could no longer be induced when the dark interval exceeded 0.33 s in medium with 4.5 g/liter methyl cellulose and 0.23 s in medium without it. The ratio of the critical dark period between repeated light pulses to the rotational period was always about 0.5, although the rotational period was lengthened 1.4 times with methyl cellulose. Thus, the present results clearly demonstrated that it is this ratio which is crucial for phototaxis, rather than the absolute length of the critical dark period.

Bleaching of F-Centers and Formation of Complex Centers in Gamma-Irradiated KCl at Room Temperature

The optical bleaching of F centers in gamma-irradiated KCl at various dosage was measured. The amount of F centers which bleached quickly, denoted by N q , was studied as a function of irradiation dose and bleaching temperature. It was found that N q includes the decrease of F center concentration due to complex center formation and due to recombination with positive holes, that the latter part of N q is closely related to the F centers formed in the first stage of gamma-irradiation, and that the complex centers are only formed by the bleaching of F centers formed in the second stage of irradiation. The rate of complex center formation by intermittent light pulses was studied, the results indicating that the amount of complex centers formed by a given number of pulses depends on the time interval between successive light pulses. The relaxation time for the formation of complex center was obtained at various temperatures from these results, and the activation energy (0.95±0.2) eV was obtained. An analysis ...

Low-frequency dynamic response of photosensitive neon discharge tubes

The instantaneous response to illumination of photosensitive discharge tubes in relaxation oscillation circuits has been investigated, using light sources of periodically varying light output to irradiate the tubes. A brief theoretical outline is given of the effect of periodic variations on sawtooth oscillations and this is applied to the oscillations of neon discharge tubes illuminated by sources giving a light output of rectified sinusoidal waveform. Photographs are given of oscillation traces of tubes illuminated by light from mercury vapour lamps and by intermittent light pulses. It is shown that, under certain conditions, a complete delineation of the light output waveform is obtained. This method can be used for the determination of the light variation frequency or for studying the waveform of the light output from a source.