Using the Light Intensity Logger

In LabVIEW, the programs are called VI (short for Virtual Instruments). This VI uses the Photodiode on the Light Application Adaptor to measure the light intensity. The result is shown as the value in LUX and a light meter. It also charts the light intensity over time. The update rate is settable from 0 to 2 sec. There is also an alarming function if the light intensity exceeds the set value. The VI also shows basic statistics like Max, Mean and Min light intensity value. The values are calculated only when the VI stops.

  1. Click to run the VI.

  2. Change the ambient light intensity by covering the photodiode with your hands. Observe how the meter and its associated digital display are able to monitor the changes and report the results in Lux. Alternatively shine a torchlight or other light source onto the photodiode to change the light intensity.

  3. A chart is very useful to observe the trend of the light intensity changes. It is very easy to create charts in LabVIEW. There are two plots for this chart – one displaying the measured light intensity (yellow) and the other the Alarm Limit (red).

  4. For data loggers, it is very common to include alarms whenever limits allowed are exceeded. Use the Operating tool to change the High Limit. You can use the increment or decrement arrows on the control, or drag the pointer to the desired values.

  5. If you are using a torchlight to increase the light intensity, set the High Limit above the ambient value. If you are blocking the ambient light, set the High Limit lower. Observe the Limit LED. It changes color when the High Limit is exceeded.

  6. You may be logging data from periods as short as minutes to as long as days. Changing the update period (how often the light intensity is measured) is a very common feature. Use the Operating tool to change the Update Period and observe the change. The DAQ card you are using has a maximum acquisition rate of 100 samples/sec so this will limit the lower end of the Update Period.

  7. Press to stop the VI

  8. If this data logger were used in a greenhouse, it may be useful to know the maximum and minimum light intensities measured during the measurement period. Statistic functions in LabVIEW allow the user to read off these values. In this example, the results are displayed only when the program ends.

  9. Close the VI and do not save changes.

End of Exercise 1

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