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[en] Historic estimates of daily global solar irradiation are often required for climatic impact studies. Regression equations with daily global solar irradiation, H, as the dependent variable and other climatic variables as the independent variables provide a practical way to estimate H at locations where it is not measured. They may also have potential to estimate H before 1953, the year of the first routine H measurements in Canada. This study compares several regression equations for calculating H on the Canadian prairies. Simple linear regression with daily bright sunshine duration as the dependent variable accounted for 90% of the variation of H in summer and 75% of the variation of H in winter. Linear regression with the daily air temperature range as the dependent variable accounted for 45% of the variation of H in summer and only 6% of the variation of H in winter. Linear regression with precipitation status (wet or dry) as the dependent variable accounted for only 35% of the summer-time variation in H, but stratifying other regression analyses into wet and dry days reduced their root-mean-squared errors. For periods with sufficiently dense bright sunshine observations (i.e. after 1960), however, H was more accurately estimated from spatially interpolated bright sunshine duration than from locally observed air temperature range or precipitation status. The daily air temperature range and precipitation status may have utility for estimating H for periods before 1953, when they are the only widely available climatic data on the Canadian prairies. Between 1953 and 1989, a period of large climatic variation, the regression coefficients did not vary significantly between contrasting years with cool-wet, intermediate and warm-dry summers. They should apply equally well earlier in the century. (author)
[en] Light pipe systems (LPS) are simple devices that allow the transmission of daylight into interiors of buildings. It is a convenient concept for illumination of windowless parts of buildings. The light performance of this is highly dependent on the solar altitude due to the small inlet aperture. Placing the laser-cut panel (LCP) at the entrance aperture in light pipe system, will increase the light performance during low solar angle. This paper presents the results of light performance a 400mm diameter light pipe integrated with a laser-cut panel at entrance aperture as collector. For that reason, this research adopted an experimental approach to compare the light pipe performance via 1:10 scale model. Two scale models were built. LCP in the form of pyramids was fitted at the entrance aperture of light pipe in different tilted angle 40° and 47.5°. The system has been monitored 30 minutes interval with lux meter to evaluate the improvement light performance on a working plane for 6 days under good sky condition. The results of this experiment shows that LCP with 40° tilted angle performed better than 47.5° tilted angle. The light pipe with LCP as collector the minimum recommended illuminance by Malaysian Standard (MS) 1525:2007 can be achieved as early at 8am. (paper)
[en] The structure of a modified photo detecting head with a photoresistor and spectral sensitivity V is put to consideration. The characteristics of the spectral sensitivity and the cosine error of the photodetector are shown. An electronic measuring transducer with linear dependence of the output voltage on the illumination was developed for the head. The structure of a 3-channel system for synchronous measurement and recording of the illumination within the range 0-100 klx with maximum relative error of +- 5% is presented
[en] Highlights: ► Estimation of diffuse horizontal and vertical (N, S, E, W) illuminance at Madrid. ► Monthly mean of hourly values are obtained based on a data series of 26 years. ► Tables representing the climatic behavior of diffuse illuminance are given. ► Empirical luminous efficacy models with local coefficients are used. ► The influence of the nubosity on the illuminance levels have been analyzed. - Abstract: The overall objective of this work is to provide diffuse illuminance availability at Madrid (Spain) through a statistical analysis of illuminance values corresponding to a long-term data series. The illuminance values are obtained from irradiance measurements by means of different empirical models for luminous efficacy. The values of diffuse illuminance on a horizontal and on vertical surfaces facing the four cardinal points are estimated and the different aspects related to daylight availability in an area with specific climatic conditions are analyzed. The experimental data consist of global and diffuse irradiance measurements on a horizontal surface provided by the National Meteorological Agency in Spain (AEMET) for Madrid. These data consist of hourly values measured in the period of 1980–2005. The statistical results derived correspond to a daylight typical year for the five surfaces considered. This information will be useful to building experts to estimate natural illumination availability when daylighting techniques are applied in building design with the main aim of electric energy savings.
[en] Many countries have experimented with daylight saving time (DST) to save energy and to align human activities more closely to the daily cycle of light and darkness. Using a novel methodology, we estimate the year-round energy savings to be obtained from advancing Indian Standard Time (IST), from the introduction of DST, and from dividing the country into two time zones. We find that the option of advancing IST consistently saves more energy than the corresponding DST option, which in turn saves more energy than the corresponding time zones option. This is because the energy benefits of advancing IST accrue for the entire year throughout the country, whereas the benefits of DST are confined to summer months and the benefits of two time zones are largely in the lower energy consuming eastern region. We recommend advancing IST by half-hour to being six hours ahead of UTC. This confers the advantages of DST and time zones without their disadvantages and is forecast to save more than 2 billion kWh of electricity every year during evening peaks that are difficult to supply. While these results are India-specific, similar exercises would be useful to many other countries. - Highlights: ► Advancing IST (YRDST) consistently saves more energy than the corresponding DST. ► DST consistently saves more energy than dividing India into two time zones. ► There are also many non-energy benefits of advancing IST. ► Results are for India; countries with DST may find it useful to consider YRDST.
[en] Two optically brightened commercial papers were subjected to 72 hours continuous exposure to graphic arts daylight simulating fluorescent lamps at 1.4 and 4.4 klux. At the higher illuminance level, a CIELAB colour difference of 1.0 was reached in approximately 3 and 50 hours for the two papers. The colour differences produced by the 1.4 klux exposure were greater than that predicted by assuming a linear relationship between intensity and colour change, by a factor of 1.8.
[en] For the luminance measurements reported in the present work, one sensor was used to measure zenith luminance, and 34 sensors were positioned on a dome with their collimators pointing toward different positions P on the celestial sphere, which can be specified by the values of their zenith Z and azimuth θ angles. Overcast skies values were used. The final model proposed for the mean luminance distribution for overcast skies normalized to the zenith luminance L Zθ/L z has been developed in four steps. For each value of Z, the mean value of L Zθ/L z is expressed as a ratio of gradation functions that depend on θ. Only for θ = 180 deg. , a good coincidence is obtained with the model proposed by the Commission International de l'Eclairage (CIE) for a wide range of values of Z