Solar Radiation
The Solar Radiation node uses the solar position to specify the initial direction vector of rays. The node is selected from the Physics toolbar, Global menu.
See Release for information on the following sections: Release Times, Initial Ray Frequency, Vacuum Wavelength, Initial Phase, and Initial Value of Auxiliary Dependent Variables.
Initial Coordinates
These settings are the same as for the Release from Grid node.
North, West, and the up directions correspond to the x, y, and z directions, respectively.
Source
Select an option from the Location defined by list: Coordinates (the default) or City.
For City select a predefined city and country combination from the list. Click to select the Include daylight saving time (Time zone + 1) check box to add one hour to the default setting for the city selected. For example, if New York City, USA is selected and the default standard time zone is UTC −5 hours. If the check box is selected, the daylight savings time is used instead (UTC −4 hours). This feature does not automatically deduce whether daylight savings should be applied based on the selected city and date; you must specify it explicitly.
If Coordinates is selected, or your city is not listed, in the Location table define the:
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Latitude, a decimal value, positive in the northern hemisphere (the default is Las Vegas, USA latitude, 36.1). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).
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Longitude, a decimal value, positive at the East of the Prime Meridian (the default is Las Vegas, USA longitude, −115.2). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).
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Time zone, the number of hours to add to UTC to get local time (the default is Las Vegas, USA time zone, −8). For example in New York City, USA the time zone is UTC −5 hours (standard time zone) or UTC −4 hours (with daylight savings time).
For either selection, in the Date table enter the:
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Day, the default is 01. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent days but the model’s unit for time may be different (for example, the SI unit for time is second).
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Month, the default is 10 (October). Enter a value without a unit to avoid double conversion. This is because the value is expected to represent months but the model’s unit for time may be different (for example, the SI unit for time is second).
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Year, the default is 2014. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent years but the model’s unit for time may be different (for example, the SI unit for time is second). The solar position is accurate for a date between 2000 and 2199.
For either selection, in the Local time table enter the:
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Hour, the default is 12. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent hours but the model’s unit for time may be different (for example, the SI unit for time is second).
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Minute, the default is 0. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent minutes but the model’s unit for time may be different (for example, the SI unit for time is second).
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Second, the default is 0.
The sun position is updated if the location, date, or local time changes during a simulation. Because the time scale of ray propagation is typically many orders of magnitude smaller than the time scale for significant changes in solar position, modeling ray propagation at different times of day typically requires a Parametric Sweep over the larger time scale. Note that no validity range is prescribed on the time inputs. It is possible to enter values that exceed the expected boundary. For example, entering 5h 2min 81s is equivalent to 5h 3min 21s. This makes it easier, for example, to run a Parametric Sweep over the time of day using only a single parameter.
For either selection, in the Solar irradiance field Is (SI unit: W/m2) define the incident radiative intensity coming from the sun.
Angular Perturbations
Select an option from the Corrections for finite source diameter list: None (the default), Create light cones at release points, or Sample from conical distribution.
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For None no perturbation to the initial ray direction is applied.
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For Create light cones at release points a cone-shaped distribution of rays is released at each point. Enter a value for the Number of rays in wave vector space (dimensionless) Nw (dimensionless). The default is 50. A cone-shaped distribution containing Nw rays is released at each point, which may cause a very large number of rays to be released.
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For Sample from conical distribution a single ray is released at each release point. This ray is given a random perturbation with uniform probability density within a cone-shaped distribution in wave vector space.
For Create light cones at release points and Sample from conical distribution, specify the Maximum disc angle Ψm (SI unit: rad). The default is 4.65 mrad.
For Create light cones at release points and Sample from conical distribution, select a Limb darkening model: None (the default), Empirical power law, Linear, or User defined. The limb darkening model is typically used to reduce the intensity of solar radiation that is released from the periphery of the solar disk, relative to radiation that is released near the center. For Linear enter a Limb darkening coefficient β (dimensionless). The default value is 0.8. For User defined enter a Limb darkening coefficient fL (dimensionless). The default value is 1.
The options for accounting for finite source diameter and solar limb darkening are discussed in the Illuminated Surface Theory section.