Association Between Evening Light Exposure and Subjective Sleep Measures Among People Living With Dementia

Excessive light exposure before bedtime can disrupt one’s circadian rhythm and can lead to poor sleep. The purpose of this study was to describe the relationship between evening light exposure and subjective sleep measures in people living with dementia (PLWD). We conducted secondary data analysis using the baseline data from Healthy Patterns Clinical Trial (N=137). We used Actiwatch Spectrum Plus to collect light data over three consecutive days. We defined evening light exposure as the average white light intensity for 4 hours before sleep. Sleep measures included Epworth Sleepiness Scale and PROMIS Sleep-Related Impairment. We used univariate regression analysis. We found that that greater evening intensity of light exposure was associated with higher daytime sleepiness (𝛽=0.209, p=0.015) and more sleep impairment (𝛽=0.228, p=0.014). The results of our study suggest that exposure to bright light during evening can disturb nighttime sleep and increase daytime sleepiness in PLWD.

White light intensity stabilization for long term photometric calibrations

This paper presents an overview of the design of a voice coil based white light intensity stabilization tool. A system is created capable of mechanically stabilizing the fluctuations in a beam of light. This is achieved with a use of a voice coil and simple PID based feedback loop, controlled using a LabVIEW interface. Stability results are shown using Allan deviations curves.

Long-term variation of sunspot penumbra to umbra area ratio

A typical sunspot, as seen in white-light intensity images, has a two part structure: a dark umbra and a lighter penumbra. Such distinction primarily arises due to the different orientations of magnetic fields in these two regions. In this study, we use the Kodaikanal white-light digitized data archive to analyze the long-term evolution of umbral and penumbal area. We used an ‘automated algorithm’ to uniquely identify the sunspot umbra (including the calculation of penumbra to umbra ratio) from these digitized intensity images. Our analysis reveals that the ratio increases slightly with the increase of sunspot area upto 100 μHem but eventually settles down to a constant value after that. This study, not only allows us to better understand the evolution of an individual spot and its corresponding magnetic field but this is also beneficial for solar dynamo studies which aim to reproduce such structures using a MHD theory.

Regulation of the photosynthetic apparatus under fluctuating growth light

Safe and efficient conversion of solar energy to metabolic energy by plants is based on tightly inter-regulated transfer of excitation energy, electrons and protons in the photosynthetic machinery according to the availability of light energy, as well as the needs and restrictions of metabolism itself. Plants have mechanisms to enhance the capture of energy when light is limited for growth and development. Also, when energy is in excess, the photosynthetic machinery slows down the electron transfer reactions in order to prevent the production of reactive oxygen species and the consequent damage of the photosynthetic machinery. In this opinion paper, we present a partially hypothetical scheme describing how the photosynthetic machinery controls the flow of energy and electrons in order to enable the maintenance of photosynthetic activity in nature under continual fluctuations in white light intensity. We discuss the roles of light-harvesting II protein phosphorylation, thermal dissipation of excess energy and the control of electron transfer by cytochrome b 6 f , and the role of dynamically regulated turnover of photosystem II in the maintenance of the photosynthetic machinery. We present a new hypothesis suggesting that most of the regulation in the thylakoid membrane occurs in order to prevent oxidative damage of photosystem I.

Pyruvate-dependent diauxic growth of Rhodospirillum rubrum in light

When Rhodospirillum rubrum mutant C was first exposed to radiant energy after long-term anaerobic dark growth, the cells often exhibited a diauxic growth response. This happened with pyruvate in the medium and when cultures were exposed to a less-than-growth-saturating white light intensity of about 6,460 lx. Under the growth-saturating light condition, mutant C photometabolized and growth was not affected by Na hypophosphite, an inhibitor of pyruvate fermentation. In lower intensity light, in which diauxie occurred, initial (phase I) growth occurred by fermentation of Na pyruvate and was sensitive to Na hypophosphite inhibition. Once pyruvate was depleted, phase I growth stopped, the bacteriochlorophyll content of the cells began to increase from about 3 nmol/mg of protein, and growth finally resumed phototrophically (phase II). The lag period and phase II growth were influenced by radiant energy. By changing the white light intensity from 2,150 to 753 lx between experiments, the duration of both the lag period and the generation time of cells in phase II growth increased. Diauxic growth was pyruvate dependent. It occurred with pyruvate even if malate, a photometabolizable substrate, was added to the growth medium. Moreover, the biphasic growth response was reversible. It was observed not only with R. rubrum mutant C grown cells photosynthetically, but also when other strains of R. rubrum were placed in pyruvate medium under lowered light conditions. Only R. rubrum S1 did not exhibit the typical pyruvate-dependent diauxic growth response.

The Effects of Linolenic Acid and Extracts of Ricinus Leaf on System I and System II

The action of extracts of Ricinus communis leaf (RLE) and of linolenic acid (LINO) on System I and System II of corn and spinach chloroplasts were investigated by an amperometric method.RLE induced a time dependent decrease in the rate of oxygen production by corn chloroplasts (half time about one hour) at low white light intensity (900 ergs/cm2 sec.). At high white light intensity (7 x 103 ergs/cm2 sec.) the maximum value of the oxygen gush, V0, was observed to decrease with time in the presence of RLE; the steady state rate of oxygen production, Vm, also decreased under these conditions. The ratio, V0/Vm, decreased immediately upon addition of RLE, then increased with time. The effect of RLE on System I was much more rapid than on System II. In less than one hour all activity of System I disappeared.At high white light intensity addition of 1.6 x 10-4 M LINO to spinach chloroplasts induced a time dependent decrease of V0 and increase of Vm. The latter effect is indicative of uncoupling of phosphorylation. The ratio V0/Vm decreased both with time of incubation and concentration of LINO. On the other hand, at concentrations less than 10-4 M, LINO has little effect on System I.It is concluded that both RLE and LINO may be acting on the reaction center of System II. It appears that RLE contains a fraction that specifically acts to immediately reduce the number of System I reaction centers.