Luminous Efficacy Models Research Articles

Evaluation of the Perez luminous efficacy models for a Southern Hemisphere site (New Zealand −41°S, 175°E)

The performance of the Perez models for global, diffuse and direct luminous efficacy for a Southern Hemisphere site have been evaluated using data collected at Paraparaumu Beach, New Zealand (−41°S, 175°E). All the luminous efficacy models displayed qualitatively the same trends as those measured. Quantitatively, the global luminous efficacy predicted is some 10% lower than measured at the site for all sky conditions. The diffuse luminous efficacy is also 10% lower for intermediate and overcast skies; and accurate (±3%) for clear skies. The direct luminous efficacy also showed the same 10% difference for all sky conditions. The discrepancy between measured and modelled data is tentatively attributed to differences in aerosol levels between the rural New Zealand site and the Northern Hemisphere sites used in developing the original models.

Solar irradiance and illuminance models for Japan II: Luminous efficacies

The present study was undertaken to develop simple luminous efficacy models for Japan using the data now emerging from the CIE International Daylight Measurement Programme. Kyushu University in Japan is the national and international co-ordinating centre for this programme. The models proposed herein have been evaluated against data from an independent station. Further, the estimated horizontal and global illuminances have been used to calculate vertical surface illuminances for the independent station. The results show that the method presented herein has the potential to be evaluated for other sites in Japan and world-wide.

Direct luminous efficacy and atmospheric turbidity—Improving model performance

Of all the atmospheric constituents, aerosol content is shown to be responsible for the greatest variations in direct luminous efficacy. Some clarity is brought to the comparison between Linke's and Ångström's turbidity coefficients, respectively T L and β. Grenier's recent formulation of the optical thickness of a water and aerosol free atmosphere is presented here in a simplified expression. Based on these results and Dogniaux's illuminance turbidity factor, T il, two direct luminous efficacy models are derived, one of which is tuned to our experimental data. The input parameters are optical air mass, β, and water vapour content in the tuned version. These models perform significantly better than any of twelve other models found in the literature when compared to 1 yr's measurements from each of two sites in the U.S. and Switzerland. In both sites, β was derived from horizontal visibility estimated in a nearby airport.

Direct luminous efficacy and atmospheric turbidity--improving model performance

Of all the atmospheric constituents, aerosol content is shown to be responsible for the greatest variations in direct luminous efficacy. Some clarity is brought to the comparison between Linke's and Ångström's turbidity coefficients, respectively TL and β. Grenier's recent formulation of the optical thickness of a water and aerosol free atmosphere is presented here in a simplified expression. Based on these results and Dogniaux's illuminance turbidity factor, Til, two direct luminous efficacy models are derived, one of which is tuned to our experimental data. The input parameters are optical air mass, β, and water vapour content in the tuned version. These models perform significantly better than any of twelve other models found in the literature when compared to 1 yr's measurements from each of two sites in the U.S. and Switzerland. In both sites, β was derived from horizontal visibility estimated in a nearby airport.

Luminous efficacy: Evaluation of models for the United Kingdom

Daylight values are frequently required in building design and yet daylight records are unavailable for most sites in Europe. This paper presents several different approaches used for the prediction of global, diffuse and direct luminous efficacies. A much simpler luminous efficacy model is also proposed. The analysis is divided into the sections which describe luminous efficacy of direct, global and diffuse irradiance. The focus of this work is the evaluation of various models against measured data from Edinburgh. In addition, a brief description of the most common atmospheric parameters incorporated in daylight models is presented. The need for these design tools is unquestionable as the models provide the relationship between a commonly measured quantity (solar radiation) and illuminance.

Luminous efficacy models and their application for calculation of photosynthetically active radiation

From a spectral radiative transfer model, an algorithm is developed for the conversion of illuminance to different measures of Photosynthetically Active Radiation (PAR) (in W m −2 or in μEm −2s −1). This illuminance to PAR conversion may even be used in combination with a luminous efficacy model and, thus, form a photosynthetic efficacy model. In this work, two luminous efficacy models are chosen, one empirical and one derived from the above radiative transfer model. Observed PAR energy flux and PAR photon flux from seven Nordic stations (56–70°N) and illuminance from one U.S. station (43°N) are, together with observed all-wave solar irradiance from all stations, used for verification. Observed and modelled luminous efficacies agree on the average within 1% at high solar elevation under cloudless sky, while it is indicated that the illuminance, PAR energy flux, and PAR photon flux radiometers are mutually inconsistent by some 6–16%. Even differences in cosine response between radiometer types are apparent at low solar elevation under cloudless sky. In the present climates, the global radiation efficacy is 10–12% higher under an average cloudless atmosphere than it is outside the atmosphere. By introducing an average cloud deck in this cloudless atmosphere, a further efficacy increase, slightly exceeding these 10–12%, is observed. However, observations indicate that the cloud transmittance algorithm used in the radiative transfer model significantly overestimates the global radiation efficacy increase caused by horizontally inhomogeneous cloud decks.

Daylight illuminance models for the United Kingdom

This paper presents several illuminance models which may be used for precise estimation of the available daylight. In the absence of measured data, luminous efficacy models are employed to estimate illuminance from irradiance values. The paper presents two leading efficacy models and evaluates their performance against measurements. Three existing models and one new model for slope illuminance are examined.

Electrocardiographic changes and peripheral nerve palsies in toxic diphtheria: Burkhardt, Edward A., Eggleston, Cary, and Smith, Lawrence W.: Am. J. M. Sc. 195: 301, 1938

The present work discusses simulation results of annual indoor illuminance distributions for two office geometries situated in Freiburg, Germany, calculated with six different RADIANCE-based daylight simulation methods. These methods are the ubiquitous daylight factor method [P.J. Littlefair, Predicting annual lighting use in daylit buildings, Building and Environment 25 (1990) 43–54.], ADELINE 2.0 [M. Szerman, J. Stoffel, ADELINE 2.0, Radlink Technical Manual, IEA Solar Heating and Cooling, Task 12.], the classified weather data according to Herkel and Pasquay [S. Herkel, T. Pasquay, Dynamic link of light and thermal simulation: on the way to integrated planing tools, 5th Int. IBPSA Conf., Prague, Sept., 8–10, 1997, Vol. II, pp. 307–312.] and two simulation procedures based on daylight coefficients according to Tregenza, namely ESP-r version 9 series [J.A. Clarke, M. Janak, Simulating the thermal effects of daylight-controlled lighting, Building Performance (BEPAC), (1) (Spring 1998).] and a new accelerated method developed by the authors. The new method calculates 145 diffuse and three ground daylight coefficients in a single raytracing run which considerably reduces the required calculation times for an annual daylight simulation. An explicit calculation of the indoor illuminances under all 4703 annual hourly mean sky luminance distributions from the Freiburg test reference year (TRY) serves as a reference case against which the other methods are tested.The simulation results reveal that the accuracy of an annual daylight simulation method is not necessarily coupled with the required simulation time. The quality of an annual simulation rather depends on the underlying sky luminous efficacy model and whether the method considers the hourly mean direct and diffuse illuminances for each time period explicitly.The two methods relying on daylight coefficients exhibit the lowest relative root mean square errors (RMSEs) for the straightforward office geometry. The results for the advanced office show that internal illuminance contributions due to external ground reflections are only considered by the new method.