RELATIONSHIP BETWEEN LIGHT QUALITY DEPENDENCE AND IRRADIANCE ADAPTATION OF PHOTOSYNTHESIS IN Acetabularia mediterranea*

Characteristic differences in the light intensity curves of photosynthesis after growth of cells of Acetabularia mediterranea Lamour. (A. acetabulum (L.) Silva) in weak and strong white light were similar to those for red and blue light-treated cells, respectively. This indicated that responses to white light quantity and those to light quality might be causally related. Small differences in the thylakoid polypeptide composition of cells grown in high and low intensities of white light were not significant and thus did not help to clarify whether the adaptations to blue or red light, respectively, were the same. When the red to blue-light ratio was varied, keeping the total photon fluence rate constant, the photosynthetic capacity (red light saturated O₂-production) was dependent on blue light irradiance in a logarithmic fashion. The specific influence of red light was not detectable, indicating that only blue light was effective for light irradiance adaptation in Acetabularia. The situation was different, at least for a transient period, when adaptation to light irradiance was allowed to proceed from a low photosynthetic activity after preirradiation of the cells with prolonged red light. The effect of low white light irradiances was pronounced, causing a maximum increase of photosynthetic activity within 3 days. The response to blue light was enhanced as well, and a very low photon irradiance added to continuous red light caused a change of the same order as that produced by high irradiances of blue light alone. This elevated action of low intensity white and blue light is most likely due to increased metabolite supply derived from the degradation of starch enhanced by this light quality. Therefore, photosynthetic effectiveness in Acetabularia is regulated by the irradiance of blue light and by feedback via photosynthetic products.     

Measurement of the Optical Properties of Leaves Under Diffuse Light

Measuring leaf light absorptance is central to many areas of plant biology including photosynthesis and energy balance. Absorptance is calculated from measured values of transmittance and reflectance, and most such measurements have used direct beam light. However, photosynthesis and other processes can differ under direct and diffuse light. Optical properties under diffuse light may be different, but there have been technical difficulties involved in measuring total reflectance of diffuse light. We developed instrumentation to measure this reflectance using a chopped measuring beam delivered alternately to sample and reference integrating spheres, and lock-in detection. We also built instrumentation for measuring transmittance of diffuse light. We developed standards to calibrate our instruments and correct for substitution error, a known systematic error with integrating sphere-based measurements. Helianthus annuus leaves measured under diffuse light reflected 5–10% more and transmitted a few percent less 400–700 nm light than under direct light. Overall absorptance was only a few percent higher under direct light, but leaves may utilize absorbed direct and diffuse light differently. For example, of the light entering the leaf, significantly more direct light than diffuse light is transmitted through the leaf, suggesting differences in localization of absorption within the leaf.     

Light Sources and Dosimetry Techniques for Photodynamic Therapy

Effective treatment delivery in photodynamic therapy (PDT) requires coordination of the light source, the photosensitizer, and the delivery device appropriate to the target tissue. Lasers, light-emitting diodes (LEDs), and lamps are the main types of light sources utilized for PDT applications. The choice of light source depends on the target location, photosensitizer used, and light dose to be delivered. Geometry of minimally accessible areas also plays a role in deciding light applicator type. Typically, optical fiber-based devices are used to deliver the treatment light close to the target. The optical properties of tissue also affect the distribution of the treatment light. Treatment light undergoes scattering and absorption in tissue. Most tissue will scatter light, but highly pigmented areas will absorb light, especially at short wavelengths. This review will summarize the basic physics of light sources, and describe methods for determining the dose delivered to the patient.     

Optimized Aluminum Reflector for Enhancement of UVC Cathodoluminescence Based-AlGaN Materials with Carbon Nanotube Field Emitters

The far ultraviolet C (UVC) light sources based on carbon nanotube (CNT) field emitters as excitation sources have become promising light sources for sterilization, disinfection, and water purification. However, the low light extraction efficiency of UVC–CNT light sources still hinders the practical application of these structures. Herein, we report an optimized aluminum (Al) reflector to enhance the light extraction efficiency of UVC–CNT light sources. Optical analysis of UVC-CNT light sources covered by the Al reflectors with various thicknesses ranging from 30 to 150 nm was performed to realize the optimized reflector. The UVC-CNT light sources exhibit the highest light extraction efficiency when the Al reflector layer has an optimized thickness of 100 nm. For comparison, the cathodoluminescence (CL) spectra were recorded for UVC–CNT light sources with and without the optimized Al reflector. The measured light output power and the estimated power efficiency of the UVC–CNT light-source-tube with Al reflector were enhanced by about 27 times over the reference. This enhancement is mainly attributed to the outstanding reflection effect of the Al reflector.     

Regulation of neurite outgrowth by intermittent irradiation of visible light

The effect of neurite outgrowth of PC12 cells on collagen-coated glass plates under intermittent light irradiation at 525 nm and 0.4 mW/cm2 of intensity was investigated. Neurite outgrowth of PC12 cells was significantly suppressed when PC12 cells were cultivated under intermittent light irradiation with a total irradiation time of more than 2 min/h. No temperature increase was observed in the culture medium under either continuous or intermittent light irradiation. Therefore, suppression of neurite outgrowth under light irradiation was not due to the increase of temperature in the culture medium, but rather the effect of light on the PC12 cells, especially the signal transmittance of light to PC12 cells. The light irradiation interval also affected the neurite outgrowth of PC12 cells when the total irradiation time was constant. A high extension ratio of neurite outgrowth was observed under a long time interval of nonirradiation between light irradiations (1 min of irradiation every hour) as compared with frequent light irradiation intervals (5 s of irradiation every 5 min) with the same total irradiation period per hour. The neurite outgrowth ratio was thought to be dependent on the light intensity, the total time of light irradiation in the intermittent light irradiation, and the interval of light irradiation in the intermittent light irradiation.     

The effect of polarized versus nonpolarized light on melatonin regulation in humans

The aim of this study was to compare the effects of polarized light versus nonpolarized light on melatonin secretion in healthy, humans (mean age, 25 years; N = 6). On separate evenings, each subject was exposed to four different light intensities (20, 40, 80 and 3200 lx) of both polarized and nonpolarized light, as well as to a control, dark exposure. Each evening experiment consisted of a 120 min dark exposure (0000-0200 h) followed by a 90 min light exposure (0200-0330 h). Subjects' pupils were dilated prior to exposures. Blood samples were drawn at the start and end of each light-exposure period and later assayed for melatonin by radioimmunoassay. When compared to control exposures, both polarized and nonpolarized light elicited significant suppression of plasma melatonin at each illuminance (P < 0.03 to P < 0.0001), There were no significant differences between the effects of polarized light and nonpolarized light at any illuminance. The two light stimuli modalities demonstrated very similar fluence-response relationships between illuminance and melatonin suppression. Thus, the human pineal gland is responsive to ocular exposure with polarized light in a dose-dependent manner similar to that of nonpolarized light, although no significant differences were detected between polarized and nonpolarized light on melatonin regulation.     

PHYTOCHROME-MEDIATED PHOTOTROPISM IN PROTONEMATA OF THE MOSS Ceratodon purpureus BRID

Abstract— Protonemata of the moss Ceratodon purpureus cultured in white light were transferred to darkness for 3 days and then used for phototropic experiments. Irradiation of the apical region of vertically position protonemata with small beams (0.2 mm) of red light induced a growth response towards the irradiated side (positive phototropism). The phototropic response showed irradiance dependence. The effect of red light was completely reversed by far-red light following red light irradiations, demonstrating that phytochrome was the photoreceptor pigment. Far-red light or UV-blue light had no influence on either bulging or phototropism. Experiments with linearly polarized red or far-red light showed a different dichroic distribution of phytochrome in its different forms, the red-absorbing form, P_r and the far-red-absorbing form, P_fr. Red light with a vibration plane parallel to the long axis of the filaments was most effective. The effectiveness of far-red light was expressed best when its vibration plane was 90° to the electrical vector of the inductive red light.     

Sterilization system using microwave and UV light

We constructed a novel microwave–UV light sterilization system and investigated its sterilization effect. This sterilization system can emit UV light by irradiation of microwave without other power. When irradiating UV light with and/or without microwave on aqueous DMPO solution, active oxygen species such as hydroxyl radical or superoxide were generated in the solution. The amount of active oxygen species generated by irradiation of microwave and UV light was larger than that by irradiation of UV light alone. This would be due to the promotion of emission of UV light photons by microwave and UV light irradiation. Moreover, microwave–UV light sterilization was highly effective to sterilize microorganisms. The generation of active oxygen species would play an important role in sterilization of the sterilization system.     

THE PHOTOBIOLOGY OF Paphiopedilum STOMATA: OPENING UNDER BLUE BUT NOT RED LIGHT

Abstract— The responses of stomata from Paphiopedilum harrisianum , Orchidaceae, to light and CO₂ were studied in epidermal peels. Stomatal opening under red light was indistinguishable from that in darkness, whereas blue light promoted opening above dark levels. The ineffectiveness of red light in causing stomatal opening was confirmed in the presence of 100 μ M KCN; average apertures in both darkness and red light were 53% of those measured in the absence of the inhibitor, whereas under blue irradiation, the KCN inhibition was only 30%, with average apertures two-fold of those measured under red light or darkness. Fluence rate response curves under blue light were typical of a single photoreceptor; removal of CO₂ increased aperture values without a significant light-CO₂ interaction. The lack of a stomatal red light response contrasts with results obtained in species with chlorophyllous stomata in which red light consistently causes stomatal opening, and suggests that the previously reported red light responses in stomata from intact Paphiopedilum leaves resulted from indirect effects, such as depletion of intercellular CO₂ by mesophyll photosynthesis. In isolation, Paphiopedilum stomata appear to rely on a blue light photosystem for their responses to light and fail to open under red light because of their lack of guard cell chloroplasts.     

New Phosphors for White LEDs

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or UV LEDs) and photoluminescence phosphors. GaN-based highly efficient blue InGaN LEDs combined with phosphors can produce white light. These solid-state LED lamps have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability, and long operating lifetime (about 100,000 hours). For the purpose of development of high energy-efficient white light sources, we need to produce highly efficient new phosphors, which can absorb excitation energy from blue or UV LEDs and generate emissions.In this paper, we investigate the development of blue or UV LEDs by the appropriate combination of new phosphors which can lead us to obtain high brightness white light. The criteria of choosing the best phosphors, for blue (380-450 nm) and UV (360-400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance light between the light emission from blue LEDs and the yellow YAG:Ce,Gd phosphor is important to obtain white light with high color temperature. The phosphors with high efficiency which can be excited by UV LEDs are important to obtain the white light with high color rendering index.     

Intraperitoneal Photodynamic Therapy: Comparison of Red and Green Light Distribution and Toxicity

Abstract— The aim of this study was to compare red (652 nm) and green (514 nm) light for photodynamic therapy (PDT) of the peritoneal cavity with emphasis on light distribution and toxicity. Red-light PDT was limited by intestinal toxicity and it was hypothesized that less penetrating green light would allow higher light doses to be used in the peritoneal cavity. Female non-tumor-bearing rats were photosensitized with mTHPC (meta-tetrahydroxyphenylchlorin, Foscan®) intravenously or intraperitoneally and the peritoneum was illuminated using a minimally invasive technique. For both red and green light, the time of illumination was varied to give the required dose. Light fluence rate was measured in situ at multiple sites within the abdominal cavity. The toxicity experiments were carried out with a total of 160 J incident red or 640 J incident green light and a drug dose of 0.15 mg/kg Foscan® For red light a mean fluence rate of 55.2 38.5 mW cm ₂ was measured, with a peak fluence rate of 128 mW cm ₂ on the intestines. For green light the mean and peak fluence rates were 8.2 9.0 (i.e. including zero fluence rate measurements) and 28 mW cm ₂, respectively. Intestines were most vulnerable to red light illumination. The intravenous injection route resulted in increased toxicity for red light, but for green light there were no major differences between intravenous and intraperitoneal routes. The 4 h interval between drug and illumination resulted in very little toxicity for both wavelengths. We conclude that for intraperitoneal PDT green light allows higher light doses than red light, but the light distribution over the peritoneum is much less favorable and may not be suitable for whole peritoneal illumination using a minimal-access technique.     

LIGHT-INDUCED INFRARED LIGHT SCATTERINGSIGNAL IN THE RETINA: EFFECT OF PHOSPHODIESTERASE INHIBITORS

Visible light changes IR light scatter through a toad retina. This signal presents three components: at low light intensity (100-400 bleached rhodopsins/rod) an early decrease in IR light scatter, of small amplitude, with time to peak of 1-6 s; at intermediate light intensity (1200-16,000 bleached rhodopsins/rod) a slow increase in IR light scatter, with time to peak of 10-30 s; at high light intensity (50,000-160,000 bleached rhodopsins/rod) a last increase in IR light scatter, with time to peak of 1 min. Light sensitivity, amplitude and time to peak of the last two components are increased by inhibitors (3-isobutyl-1-methyl-xanthine and papaverine) of the cyclic 3'5' guanosine monophosphate phosphodiesterase.     

Quantitative Photoswitching in Bis(dithiazole)ethene Enables Modulation of Light for Encoding Optical Signals

Using one ray of light to encode another ray of light is highly desirable because information in optical format can be directly transferred from one beam to another without converting back to the electronic format. One key medium to accomplish such an amazing task is photoswitchable molecules. Using bis(dithiazole)ethene that can be photoswitched between its ring‐open and ring‐closed states quantitatively with excellent fatigue resistance and high thermal stability, it is shown that quantitative photoreversibility allowed the photoswitching light to control other light travelling through the photoswitchable medium, a phenomenon of transferring information encoded in one light ray to others, thus imparting photo‐optical modulation on the orthogonal light beam.     

THE MODE OF INTERACTION BETWEEN BLUE (UV) LIGHT PHOTORECEPTOR AND PHYTOCHROME IN ANTHOCYANIN FORMATION OF THE SORGHUM SEEDLING

Two non-photosynthetic photoreceptors (phytochrome and a blue light photoreceptor) are involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings. The present study was undertaken to investigate the kind of interaction between phytochrome and the blue light photoreceptor. The data show that phytochrome (P_fr) can only act once a blue light effect has occurred. On the other hand, the blue light effect cannot express itself without P_fr. It is concluded that there is an obligatory dependency (or sequential interaction) between the blue light effect and the light effect occurring through phytochrome, although the blue light photoreaction per se is not affected by the presence or absence of phytochrome. The latter statement is based on the results of dichromatic experiments, i.e. simultaneous, high fluence rate irradiation with two kinds of light. Blue light can be replaced by UV light. It is not clarified yet whether the effect of blue and UV light is due to the same photoreceptor.     

INFLUENCE DES ÉCLAIREMENTS APPROXIMATIVEMENT MONOCHROMATIQUES SUR LE DEVELOPPEMENT DES TISSUS DE MOELLE DE TABAC CULTIVBS IN VZTRO EN PRESENCE D'AUXINE ET DE KINETINE

Abstract— The influence of relatively monochromatic light (around 4350, 5250, 6600 and 8000 Å) on the growth of cultures of tobacco pith tissues with auxin and kinetin was studied. The cultures were subjected either to continued light or to alternations of 16 hr light with 8 hr darkness, or to a dark period followed by continuous light.
The influence of blue light was especially noted. The development in volume and weight of the cultivated tissues in blue light is generally less than in the other conditions (except for one or two exceptions); the differences are attenuated when a light period alternates with a period of darkness; the callus tissues of tobacco pith exposed to blue light are always chlorophyllic with a dense and hard appearance and histological studies show that tissues grown in blue light are mostly made of large cells with thick cell-walls and many nodules while under the other conditions the tissues are mostly made of very small cells with few or no nodules.
These differences seem related to specific photoreceptors rather than to energies delivered to the cultures.     

White-light-induced fragmentation of methane

We experimentally probe molecular ionization and dissociation of methane molecules in the gas phase upon their irradiation by intense pulses of white light that spans the wavelength range 500-850 nm. White light pulses are generated upon irradiation of BK7 glass by 36-fs-long pulses of intense 820 nm laser light. Comparison is made of the molecular fragmentation patterns obtained using white light that is depolarized with those obtained using single-color (820 nm) light that is highly chirped. On the basis of such comparison, we make hitherto-unavailable estimates of the in situ intensity of white light pulses. Results obtained using white light also indicate that resonances apparently do not play any role in the ionization dynamics that ensue upon irradiation by intense, broadband light; neither are the dynamics affected by the polarization properties of the 820 nm light that is used to generate the white light.     

SIMILARITIES IN THE INDUCTION OF SYNTHESIS OF A CELL-SURFACE POLYPEPTIDE IN Arthrobacter sp. BY NEAR-UV IRRADIATION and PHOTODYNAMIC CONDITIONS

Irradiation of aerobic suspensions of Arthrobacter sp. with near-UV light (310-400 nm) induced synthesis of a 21 000 dalton, cell-surface polypeptide. Synthesis of this polypeptide also was induced by visible light in the presence of photodynamic dyes, as shown previously (Hoober, 1978). Induction of the polypeptide in near-UV light and with visible light plus dyes was inhibited by histidine. Hemin inhibited induction in near-UV light and in visible light with methylene blue, neutral red and acrifiavin, which are cationic dyes, but failed to inhibit induction in visible light with rose bengal, an anionic dye. These results suggested that inhibition by hemin required electrostatically favored interaction between the anionic porphyrin and the sensitizer, and that the near-UV light effect was mediated by a cationic or neutral endogenous sensitizer. The similarities in the responses of the cells to near-UV irradiation and visible light plus dyes suggested that the mechanism of induction under the two conditions was the same.     

Heteroblastic Development and Shade-avoidance in Response to Blue and Red Light Signals in Acacia implexa

Information from blue (400–500 nm) and red (660–730 nm) wavelengths is used by plants to determine proximity of neighbors or actual shading. Plants undergo trait changes in order to out-compete neighbors or accommodate shading. Heteroblasty, the dramatic shift from one leaf type to another during juvenility, can be influenced by the light environment although it is unknown whether cues from blue or red (or both) are driving the developmental process. Seedlings of three populations of Acacia implexa (Mimosaceae) collected from low, medium and high rainfall habitats were grown in a factorial design of high/low blue and red light to determine how light signals affect heteroblasty and patterns of biomass allocation. Low blue light significantly delayed heteroblasty in the low rainfall population and low red light significantly delayed in the low and high rainfall populations. Low blue light increased stem elongation and decreased root biomass whereas low red light induced a strong shade-avoidance response. These results were consistent across populations although the low rainfall population showed greater trait variability in response to red light signals. We conclude that red light conveys a greater information signal than blue light that affects heteroblasty and seedling development in A. implexa .