9.2 Photosensor System Performance Plots

View Correlations – The View Correlations buttons allow the user to select which correlation graph to view. The red button indicates the correlation graph currently displayed. The correlation graph is shown to the right and represents the variation in sensor readings that the selected photosensor / luminaire zone combination experiences throughout a year for sunny and cloudy conditions. The ideal correlation graph will be very linear between the cloudy, sunny, and electric lighting conditions. In other words, the blue, pink, and green dots should be linearly aligned. The green horizontal line represents the current target design illuminance.

The red line or lines (if you have a high and a low setpoint or sliding setpoint) appear on this graph and indicate the current setpoint relative to the array of sky condition data. The point the red line crosses the green design illuminance line is the current signal setpoint. This line will default to a nighttime condition, so it will initially be lined up with the average electric lighting conditions plotted. This correlation graph can be used to determine the best sensor signal setting. Essentially, any sky condition data point that falls below the green design illuminance line and below the red signal setpoint line will be a sky condition that may have a less than adequate resulting illuminance. Therefore, the setpoint setting should be made such that all points fall above the red line or green design illuminance line. It’s up to the user to find their desired balance between energy savings and resulting illuminance. For sliding setpoint systems, it is also critical for any green electric lighting correlation points to fall above and to the left of the scattered daylight correlation points. If this condition does not exist, the sliding setpoint is essentially reduced to a constant setpoint system and the settings have to be relaxed to achieve adequate maintained illuminances.

View Illuminance – Upon assigning a photosensor scenario for each luminaire zone, the graph and the last couple of columns of the table are updated to reflect the current settings. The graph, shown to the right, presents the resulting workplane illuminances for each day that has been calculated. The target design workplane illuminance is indicated with a green horizontal line. From this graph, it is easy to see which days, if any, will have lower than desired average or minimum illuminance. The user can then interactively adjust the photosensor combinations and settings until they are satisfied with the performance on the given set of sample days.

View Light Output – The annual hourly Light Output for the design days are displayed when the View Light Output (ie. Dim Z1 ) buttons are pushed. The graph shows the predicted light output for the selected electric lighting zone for the various design day conditions throughout the year.

The Change Scale button on this graph allows the user to change the Y-axis scale of this graph for better readability.

The Smoothed button allows the user to change the plot type from a linear point-to-point to a spline fitted curve.