Daily Total Radiation Research Articles

Modeling of a helioabsorption heat pump system for hot water supply

THE PURPOSE. A domestic hot water supply system is proposed, combining a solar collector and a heat pump for the climatic conditions of the city BAC NINH - VIETNAM, capable of providing hot water to 5 users all year round. Justify the performance of the proposed system under these conditions. METHODS. The solution of the problem was carried out experimentally and by the method of mathematical modeling. The mathematical model is based on the energy balance equations taking into account the efficiency factors. The scheme and principle of operation of the pilot plant and the results of the calculation of the combined hot water supply system based on the monthly average values of the total daily radiation for the location of the solar collector are presented. The system contains a solar collector with vacuum heat-absorbing tubes and an air heat pump as energy sources. With sufficient solar radiation, hot water is generated entirely from the heat-absorbing vacuum tubes, stored in the reservoir of the solar collector and passes through the reservoir of the heat pump to the consumer when the heat pump is not working. In case of insufficient solar radiation, the air heat pump is switched on.RESULTS. The calculation of the power of the solar collector based on the average monthly values of the total daily radiation and the efficiency of the solar collector, the amount of heat added to the solar hot water supply system, the heat capacity of the heat pump, and a heat pump for the hot water supply system was selected. CONCLUSION. The results of the experiments confirm the calculations for replenishing the heat deficit for the solar collector with an air heat pump of low power at any time of the year. The calculations are made for a system that provides hot water for the daily needs of five and three people. It is shown that the low heating capacity of the heat pump allows one to reduce the cost of initial investment in domestic hot water supply systems with a solar collector and, accordingly, the prospects of the proposed hot water supply system in Vietnam.

Study on matching characteristics of photovoltaic disturbance and refrigeration compressor in solar photovoltaic direct-drive air conditioning system

This paper presents a 3 HP solar direct-drive photovoltaic air conditioning system which operates without batteries, ice thermal storage is used to store solar energy. The refrigeration compressor will suffer from loss of power even cannot startup or shut down if the PV power generation suddenly fluctuates. In the case of the solar radiation fluctuations to keep the system running continuously and steadily, that requires a proper system design to match the power consumption of solar air conditioning system with a proper PV capacity, matching an adaptive controller and a suited compressor simultaneously. Solar air conditioners with different capacity of PV panel, with and without MPPT controller and different types compressors were built and tested outdoors to experimentally investigate the matching characteristics of photovoltaic disturbance and refrigeration compressor. The experimental results of the system with a variable speed compressor and a MPPT controller have shown good ice-making performance and reliable operation as well as a great improvement in the available solar energy. Finally, the highest system COP reached 0.289 when the cumulative daily total radiation was 18.2 MJ/m2 in Kunming, China. The research work shows that the direct drive ice storage by solar photovoltaic system has a certain application prospect in the regions where the electricity is tight but requiring cooling.

Correlation between the distribution of solar energy resources and the cloud cover in Xinjiang

In order to study the influence of cloud cover on solar energy resources, it provides scientific basis for the development and utilization of solar radiation resources. Based on the Cloud and the Earth’s Radiant Energy System (CERES) and European Centre for Medium-Range Weather Forecasts (ECWMF) data from 2014-2018, the correlation between the temporal and spatial distribution of solar energy resources and the cloud cover in Xinjiang was studied and analyzed. The results show that solar energy resources have generally shown an upward trend in the past five years, with an average annual radiation of 7206.5 MJ/m2 and very stable. The overall distribution of solar radiation is mainly dominated by latitude, decreasing from south to north, and the change is relatively uniform. The maximum value of annual total radiation in the southern area of Xinjiang is about 9000 MJ/m2, which is 1.5 times of that in the northern area. The maximum daily total radiation is 28.88 MJ/m2 in July, which is 3.3 times of that in December. The total radiation in summer can reach up to 2200 MJ/m2, which is 2.2 times of that in winter. Summer radiation is high but fluctuating, and winter radiation is small but relatively stable. The autumn is the period with the least amount of total cloud during the year, the cloud cover in the northern area is about 40%, and the winter in the northern area is the highest along the foothills of the Tianshan Mountain, up to 70%. The fitting effect of radiation attenuation and cloud cover in the northern area is higher than that in the southern area, and the maximum correlation coefficient is 0.98 in summer and the minimum is 0.571 in winter. The fitting effect of radiation attenuation and cloud cover in the northern area is higher than that in the southern area, and the maximum correlation coefficient is 0.98 in summer and the minimum is 0.571 in winter. The solar radiation is mainly affected by clouds in summer, while in winter, there are other factors such as aerosols.

Analysis of Experimental Solar Radiation Data for Osogbo, Nigeria

An analysis of measured global solar radiation (GR) in Osogbo (7.77oN, 4.57oE, 288m) is presented in the form of hourly average, monthly average and percentage frequency distribution. The experimental data corresponds to a year data of 2017. The results reveal that the monthly average values of daily total radiation exhibit seasonal variation with maximum value in dry season month of March (16.59MJ/m2) and minimum value in wet season month of August (8.98 MJ/m2). The annual average GR value is 14.20 MJ/m2 while the annual cumulative GR is 5122 MJ/m2. The solar radiation climate of Osogbo has also been compared to those reported for a number of locations. The percentage frequency of days possessing irradiation rate greater than 15 MJ/m2 is 14 percent whereas that possessing less than 10 MJ/m2 is 61 percent. We conclude, based upon the above analysis that Osogbo is characterized by relatively low global solar radiation.

Reduction in the Solar Radiation Transmittance of Greenhouses Covered with Plastic Films

The reduction in solar radiation transmittance(SRT) because of dust and other foreign materials was experimentally tested in two types of greenhouses with the intent to obtain basic data for establishing maintenance and management guidelines for greenhouse cover materials. The test results in the greenhouse in Gyehwa-do estimated the amount of removed dust at 16.8– 1,021.6 mg·m-2(average: 520.7 mg·m-2), and the dust amount varied widely with the measurement points. The SRT measured in triplicate before and after dust removal ranged 68.5–80.9% and 80.9–87.2%, respectively; thus, there was an improvement in SRT by about 8.1% after dusting. In contrast, the greenhouse in Gyeongsang National University did not exhibit great fluctuations in the coefficient of determination(correlation coefficient) regardless of the daily total, average, or maximum horizontal surface radiation; the SRT gradually decreased over time. The SRT increased or decreased, showing clearly different patterns in summer and winter half years, as did the coefficients of determination(0.468–0.828). Dust was measured to be in the range 747.1– 983.1 mg·m-2(average: 840.1 mg·m-2), without great differences between the measurement points, unlike in the case of the greenhouse in Gyehwa-do. The SRT measured before and after the dust removal ranged 73.0–80.5% and 81.0–88.6%, respectively, showing an average improvement of about 7.9%. The SRT measured after washing with water ranged 88.7–90.6%, demonstrating a greater improvement with an average increase rate of 13.0%, which is 5.1% higher than the increase rate after dust removal. These results suggest that although washing with water rather than dust removal improves SRT to a greater extent(13.0% vs. 7.9%), dust removal alone is considered to provide considerable improvement in SRT. Comparison of the images of the unused film and pre-dusting film under the microscope revealed that foreign materials such as dust were adhered to the pre-dusting film, and variations were observed according to the magnification ratio and photographed area.

The Calculation of Radiation and Optimum Tilt Angle on the Inclined Plane of South-Facing Collector in Winter Months

In solar applications, collectors are usually installed with a tilt angel to obtain the maximum amount of radiation. In this paper, the anisotropic model -Hay model was used to calculate the daily total radiation on the tilt face and theoretical analysis was used to get the optimum tilt angel of southern collector face in winter months. Then the diffused radiation on horizontal face was obtained by using the isolation between daily total radiation and daily diffused radiation. Computer program was written to calculate the month radiation under different tilt angel and the maximum angel corresponding to the maximum month radiation was found. At last, the two results were compared and analyzed.

Summertime N2O, CH4 and CO2 exchanges from a tundra marsh and an upland tundra in maritime Antarctica

This study provides the first concurrent measurements of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a tundra marsh and an upland tundra in maritime Antarctica over the summers of 2007/2008 and 2011/2012. Tundra N2O and CH4 fluxes showed large spatial variations depending on local hydrological regimes. N2O sinks generally occurred at waterlogged marsh sites (−3.0 to 27.5 μg N2O m−2 h−1) whereas relatively dry and mesic sites presented weak or strong N2O sources (2.2–41.6 μg N2O m−2 h−1). Upland tundra sites showed negligible N2O emissions due to low soil TN and NH4+–N contents. Dry/upland tundra sites showed weak to strong CH4 uptake (−4.5 to −85.8 μg CH4 m−2 h−1). The waterlogged sites showed weak to strong CH4 emissions (29.8 μg CH4 m−2 h−1–2.4 mg CH4 m−2 h−1). Both tundra marsh and upland tundra experienced a large net CO2 uptake with the greatest mean CO2 uptake rate (−92.1 mg CO2 m−2 h−1) at dry marsh sites. Mean ecosystem respiration (ER) ranged between 82.5 ± 13.2 and 174.9 ± 25.7 mg CO2 m−2 h−1 at all the sites, and showed a strong exponential correlation (P < 0.001) with 0–10 cm soil temperature. Gross photosynthesis (Pg) was more than two times higher in tundra marsh than in upland tundra due to the difference of vegetation coverage. N2O flux showed a strong negative correlation (P < 0.01) with 0–10 cm soil temperature at the marsh sites, and significant or weak positive correlations with total daily radiation (TDR) and sunlight time (ST). No significant correlation was obtained between CH4 fluxes and environmental variables at tundra marsh and upland tundra sites. There was a significant negative correlation (P < 0.01) between NEE and 0–10 cm mean soil temperature, total daily radiation. Our results indicated that the lowering of water table significantly increased N2O emissions and CH4 consumption, but decreased C loss from the tundra marsh. In the future, the combination of climate warming and frequent precipitation will alter tundra hydrological conditions, and thus decrease N2O emission and CH4 consumption from maritime Antarctic tundra.

Investigation of Absorption Cooling Application Powered by Solar Energy in the South Coast Region of Turkey

In this study, an absorption system using ammonia-water (NH3-H2O) solution has been theoretically examined in order to meet the cooling need of a detached building having 150 m 2 floor area for Antalya, Mersin and Mugla provinces in Turkey. Hourly dynamic cooling load capacities of the building were determined by using Radiant Time Series (RTS) method in the chosen cities. For the analysis, hourly average meteorological data such as atmospheric air temperature and solar radiation belonging to the years 1998-2008 are used for performance prediction of the proposed system. Thermodynamic relations for each component of absorption cooling system is explained and coefficients of performance of the system are calculated. The maximum daily total radiation data were calculated as 7173 W/m 2 day on July 15, 7277 W/m 2 day on July 19 and 7231 W/m 2 day on July 19 for Mersin, Antalya and Mugla, respectively on the 23° toward to south oriented panels from horizontal surface. The generator operating temperatures are considered between 90- 130°C and the best result for 110°C is found the optimum degree for maximum coefficient of performance (COP) values at the highest solar radiation occurred time during the considered days for each province. The COP values varies between 0.521 and 0.530 for the provinces. In addition, absorber and condenser capacities and thermal efficiency for the absorption cooling system were calculated. The necessary evacuated tube collector area for the different provinces were found in the range of 45 m 2 to 47 m 2 . It is shown that although the initial investment cost is higher for the proposed absorption cooling system, it is economically feasible because of its lower annual operation costs and can successfully be operated for the considered provinces.

Utilização de diferentes filmes plásticos como cobertura de abrigos para cultivo protegido

This project was developed in the Faculty of Engineering - Unesp, Campus of Ilha Solteira, in the municipality of Ilha Solteira – São Paulo State. We studied the environmental behavior under two conditions of protected environment, with plastic covering the soil and bare soil. It was evaluated the quinquidial averages, averages values, maximum and minimum daily temperature and relative humidity; quinquidial averages of the daily average values of deficiency of saturation of water vapor; the density of total daily flow of radiation; from transmission to radiation in each shelter and the linear regressions to estimate the total daily radiation inside the shelter, according to the daily total radiation in field open. The protected environment reduced, in relation to the open field, the density of flow of solar radiation, with higher intensity in the shelter covered with thermal plastic film light-diffuser. The greatest effect of shelters occurred on the maximum temperature, with higher values the greenhouse covered with a conventional polyethylene film. There were no differences for air relative humidity between greenhouses. The black plastic mulching increased the soil temperature at 6 and 12 cm depth.

(P1-81) Differences between Radiation Dosages to Which the Radiology Department Staff and the Public were Exposed

IntroductionIn this study, the mean daily and annual radiation exposure of the radiology department staff, other hospital health staff, and public volunteers was compared at Maresal Cakmak Military Hospital in Erzurum, Turkey.MethodsThe NEB.211 Dose–Rate Meter with a Gaiger–Müller counter was used to measure the amount of radiation. Six radiology department health staff carried the NEB.211 device during seven working hours. At the end of the day, total absorbed dosages were noted. The same measurements were also done for the six health staff of the other departments and six non-hospital volunteers. Seventeen additional hours were noted for the non-hospital volunteers. The mean value of 17 hours of daily measurements (3.31 mSv) was added to the both group's working hours measurements and the total daily radiation amounts were calculated.ResultsThere was no statistical difference between each three groups in working hours (p = 0.087), daily and annual equivalent dosages (for both p = 0.099).DiscussionThe radiology department health staff was exposed to radiation under the border of equivalent dosage which is determined by Turkish Automic Energy Authority. Public volunteers were seen as they were exposed the radiation over the determined border of equivalent dosage. Nonetheless, with changes depending on living standards, the physical properties of living spaces and geographical circumstances per capita exposed annual dosage is about 2.4–2.8 mSv throughout the world. There was no significant statistical difference between the amounts of equivalent dosage which were exposed to the radiology department health staff, the other hospital staff and public members.

Carbon dioxide and methane fluxes in the littoral zones of two lakes, east Antarctica

During the summertime of 2007/2008, carbon dioxide (CO 2) and methane (CH 4) fluxes across air–water interface were investigated in the littoral zones of Lake Mochou and Lake Tuanjie, east Antarctica, using a static chamber technique. The mean fluxes of CO 2 and CH 4 were −70.8 mgCO 2 m −2 h −1 and 144.6 μgCH 4 m −2 h −1, respectively, in the littoral zone of Lake Mochou; The mean fluxes were −36.9 mgCO 2 m −2 h −1 and 109.8 μgCH 4 m −2 h −1, respectively, in the littoral zone of Lake Tuanjie. Their fluxes showed large temporal and spatial dynamics. The CO 2 fluxes showed a significantly negative correlation with daily total radiation (DTR) and a weakly negative correlation with air temperature and water temperature, indicating that sunlight intensity controlled the magnitude of CO 2 fluxes from the open lakes. The CH 4 fluxes significantly correlated with local air temperature, water table and total dissolved solids (TDS), indicating that they were the predominant factors influencing CH 4 fluxes. Summertime CO 2 budgets in the littoral zones of Lake Mochou and Lake Tuanjie were estimated to be −152.9 gCO 2 m −2 and −79.7 gCO 2 m −2, respectively, and net CH 4 emissions were estimated to be 312.3 mgCH 4 m −2 and 237.2 mgCH 4 m −2, respectively. Our results show that shallow, open, alga-rich lakes might be strong summertime CO 2 absorbers and small CH 4 emitters during the open water in coastal Antarctica.

Saldo de radiação em plantios de eucalipto em áreas de relevo ondulado

O conhecimento detalhado de radiação solar total que incide sobre uma região é importante para o planejamento das atividades florestais. Poucos trabalhos têm considerado a topologia da região para determinar o saldo de radiação solar (Rn), o que pode levar a erros significativos de estimativa dessa variável, dependendo do tipo de relevo predominante na região. Este estudo teve como objetivo estimar o Rn em plantios de eucalipto, levando-se em consideração a exposição do terreno em plantios florestais de eucalipto, bem como comparar essas estimativas com a estimativa em condições de topografia plana. A simulação foi realizada para os anos de 2001 e 2002, em uma microbacia do rio Doce. As encostas com orientações para o norte, nordeste e noroeste apresentaram aumentos do Rn em relação à estimativa da superfície plana, pelo fato de que, nessa época do ano, o sol, em seu movimento aparente, encontra-se ao norte da microbacia. Entretanto, as encostas com orientações para o sul, sudeste e sudoeste tiveram diminuição do Rn quando comparadas com as condições de topografia plana. A inclinação das encostas influenciou a magnitude das diferenças de ganho e perda de Rn. Quanto maiores as inclinações das encostas voltadas para o norte, noroeste e nordeste, maiores as variações, atingindo valores percentuais de aumento do Rn de até 40%, em julho. Portanto, verificou-se existir importante influência das diferentes inclinações e orientações das encostas nos totais diários do Rn.

Guidelines for Riparian Vegetative Shade Restoration Based Upon a Theoretical Shaded‐Stream Model1

Abstract: Guidelines for riparian vegetative shade restoration were developed using a theoretical model of total daily radiation received by a shaded stream. The model assumed stream shading by nontransmitting, vertical or overhanging, solid vegetation planes in infinitely long reaches. Radiation components considered in the model were direct beam shortwave on the stream centerline, diffuse atmospheric shortwave, shortwave reflected by vegetation, atmospheric longwave, and longwave emitted by vegetation. Potential or extraterrestrial shortwave irradiation theory was used to compute beam shortwave radiation received at the stream centerline, and view factor theory was used to compute diffuse radiation exchange among stream, vegetation, and atmospheric planes. Model shade effects under clear skies were dominated by reductions in receipt of direct beam shortwave radiation. Model shade effects with cloudy skies were dominated by the “view factor effect” or the decreases in diffuse shortwave and longwave radiation from the atmosphere balanced against increases in longwave radiation from vegetation. Model shade effects on shortwave radiation reflected by vegetation were found to be negligible. The model was used to determine the vegetation height (H) to stream width (W) ratios needed to achieve 50, 75, and 90 % shade restoration for mid‐latitude conditions on clear and cloudy days. Ratios of vegetation height to stream width, for dense nontransmitting vegetation, generally ranged from 1.4 to 2.3 for 75% shade restoration at a mid‐latitude site (40°N). The model was used to showH/Wneeded for E‐Wvs. N‐S stream azimuths, varying stream latitudes between 30° and 50°N, channels with overhanging vegetation, channels undergoing width changes, as well as the limits to shade restoration on very wide channels.

A Reminder of the Limitations in Using Beer's Law to Estimate Daily Radiation Interception by Vegetation

Radiation extinction coefficients for leaf canopies are often calculated using Beer's Law based on midday measurements of radiation interception. However, the assumption of Beer's Law is not appropriate for leaf canopies and this empirical approach needs to be used with caution. Alternatively, classic derivations of radiation interception by leaf canopies have resulted in a similar exponential form defined as a function of time of day, day of year, and latitude. A common experimental approach of determining the extinction coefficient from midday measurements results in a minimum coefficient that underpredicts the total daily radiation interception. Two approaches are explored to improve the estimates of daily radiation interception under a clear sky. The first approach compared extinction coefficients calculated for midday against ones calculated as representative of radiation interception over the entire day. A linear correlation was found between the two extinction coefficients so that the midday extinction coefficient could be corrected to obtain a coefficient representative of the entire day under a clear sky. The second approach estimated the time of day when measurements could be made to obtain directly an extinction coefficient representative of the entire day. While such times in the day could be identified, this approach is impractical because the periods for taking these measurements are short and dependent on leaf angle.

UV-B radiation at Penang

A new series of measurements including global and UV radiation was initiated in 1994 at Penang. These high quality data were used to study diurnal and seasonal variations. The mean daily total UV-B and global radiation is about 1.43×10 4 J and 1.77×10 7 J, respectively. Maximum radiation values for both the UV-B and global radiation are received in March and September. The daily total global radiation shows a bigger seasonal variation than UV-B radiation. On clear days, the erythemal UV radiation flux is in the high or extreme range for about 5 h beginning at around 1030 hours throughout the year. Penang (5.3°N) and Natal (6°S) are found to exhibit similar daily maximum erythemal UV irradiance values. A simple empirical relationship for the noontime UV-B flux and global irradiance in the equatorial/tropical regions has been established.

Seasonal trends in energy, water, and carbon dioxide fluxes at a northern boreal wetland

Micrometeorological measurements were made over a northern boreal fen near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem‐Atmosphere Study. The measurement period extended from the start of snowmelt until the early fall, at which time senescence was widespread throughout the fen. Data analysis concentrated on identifying seasonal trends in energy, water, and carbon dioxide fluxes and linking them to observed surface cover changes. Albedos (solar and photosynthetically active radiation (PAR)) showed large decreases over the melt period, reaching seasonal lows at the end of melt. Solar albedo increased in the summer in response to vegetation growth on the fen, while PAR albedo remained constant. Incoming and outgoing longwave flux seasonal trends were similar, so seasonal changes in net radiation were driven by the net solar flux. During the spring thaw, the melting of snow and ground ice was equal to about 28% of the daily total net radiation, while the soil heat flux accounted for about 5%. Bowen ratios at this time were above unity. Mean Bowen ratio decreased to 0.70 during the period between spring thaw and leaf‐out. As the vascular vegetation cover developed, Bowen ratios decreased to seasonal lows of 0.10–0.20 near midsummer and then increased to above unity during senescence. The daily evaporative fraction (EF) was highest (≥0.80) during midsummer when the vascular vegetation was in full leaf and actively photosynthesizing, and EF decreased to a mean of 0.55 during senescence. Eddy correlation measurements of carbon dioxide flux showed the fen acting as a net sink for CO2 only while the vascular vegetation was actively photosynthesizing with a daily mean flux of −0.81 g CO2‐C m−2 d−1 (standard error = 0.16). Before leafing and during senescence the fen was a net source of CO2. Integrated over the study period of 124 days, the fen experienced a net loss of 30.4 g CO2 m−2 to the atmosphere.

Study of hourly solar radiation data in Istanbul

This paper presents a study of the solar radiation data measured in Istanbul (41.1°N, 29.0°E) during 1992 and 1993. The monthly and annual average values of total solar radiation and clearness index are analysed. The monthly averages of daily total radiation are 1.23 kW h m −2 day −1 for January and 6.55 kW h m −2 day −1 for July. The annual average value of daily total radiation is 3.81 kW h m −2 day −1. The monthly averages of clearness index for January and July are 0.28 and 0.50, respectively. The annual average value of clearness index is 0.38. In the second part of the study, the seasonal relative frequency of hourly total radiation and clearness index is studied. 46% of the annual data corresponds to a value greater than 300 W m −2. The annual average frequency of clear hours is 24%. The analysis points to the conclusion that solar radiation will be efficient and useful between April and September for heating purposes. A polynomial relationship is developed between hourly clearness index and hourly fractional sunshine duration. Some statistical tests are used to check this relationship for four different ranges of optical air mass.

Light duration effects on carbon partitioning and translocation in tomato

The influence of light duration on carbon partitioning and translocation in young tomato ( Lycopersicon esculentum Mill.) plants growing under similar daily total radiation (DTR) was investigated. The plants were grown under an 8- or 16-h light period with a DTR of 8.64 mol m −2 day −1 for 7 days. The plants grown under both light durations fixed similar amounts of carbohydrate per day. However, the amounts of carbon translocated during the light period and over 24 h were higher in the 16-h light treatment as compared with the 8-h light treatment. The amounts of hexose, sucrose and starch accumulated during the light period and their rates of accumulation were higher in the 8-h than the 16-h light treatment. Thus, even though similar amounts of carbohydrate were fixed by plants in both treatments, more carbon was partitioned into sucrose and translocated out of the leaves in plants grown under 16-h light treatment. These results suggested that carbon partitioning and translocation in the source leaves may be directly affected by light duration or they could be indirectly affected by a light effect on sink activity. These two possibilities are discussed.

Orbital signals in the diurnal cycle of radiation

Time of day plays a critical role in determining the dominance of the Earth's orbital parameters involving eccentricity, precession, and obliquity. Extension of orbital radiation data to the diurnal cycle permits the recognition of well‐defined, temporally separate signals corresponding to all three major orbital parameters and to combinations of these parameters. Past research involving computed radiation changes at the daily and seasonal scales has not shown significant eccentricity cycles. Results of this study show: (1) at the solstices, a marked change in dominance from precession (for the solar elevation classes associated with early morning/late afternoon) to obliquity (for the elevation class containing solar noon) occurs in solar radiation; (2) at the equinoxes, cycles corresponding to those associated with eccentricity are evident in the radiation data at all individual time intervals of the day. Past studies have shown that the daily radiative total reflects only the influence of precession. A third set of cycles at the equinoxes centered near 11 kyr corresponds to a combination of orbital signals. These results imply that paleoclimatic proxy data displaying strong spectral peaks corresponding to eccentricity (100 kyr) and obliquity (41 kyr), such as records of global ice volume, may be related to radiation changes occurring in the solar elevation class containing solar noon, while paleoclimatic proxy data displaying strong spectral peaks corresponding to precession, for example, sea‐surface temperatures, appear to be showing the dominance of precession on the daily total radiation.

Nutrient solution culture of leaf lettuce under artificial light. II. Growth promotion induced by continuous illumination with low light intensity.

Extension of the period of illumination from photoperiodic to continuous was examined as a way of producing leaf lettuce (Lactuca sativa L. cv. Grand Rapids) economically under artificial light. Plants were grown under photoperiodic (17.5 hr) and continuous illumination at a total daily radiation (moles of photosynthetic photons) of 18.7 mol⋅m-2⋅day-1. The continuous illumination increased shoot fresh weight, dry weight of whole plant, stem size and chlorophyll content. Subsequently, plants were grown under continuous illumination at a photosynthetic photon flux (PPF) of 250, 350 and 450 μnol⋅m-2⋅s-1. Shoot weight tended to increase when the light intensity was decreased, while root weight had a tendency to decrease under the same conditions. Higher light intensity increased the length of the largest leaf, specific leaf area and dry matter ratio of leaves, and induced the development of tipburn. It was found that continuous illumination under low light intensity promoted the growth of leaf lettuce without causing any abnormality. These results were analysed in relation to the apparent quantum yield in photosynthesis. Since the apparent quantum yield increased with the decrease of the light intensity, growth promotion by continuous illumination under the same total daily radiation is associated with a high quantum yield. The present studies suggest that continuous illumination saves light energy more than photoperiodic illumination under equal total daily radiation, and that continuous illumination with a low light intensity at less than 250 μmol⋅m-2⋅s-1 PPF promotes the growth of leaf lettuce without causing abnormalities and contributes to the saving of lamp fixtures.