To validate that the design example now measures correctly, create a sequential number of different light intensities with the fluorescent light by using neutral density filters to attenuate the light. Different light intensities can also be created by changing the distance between the light source, and the measurement devices. However, these two methods for changing the light level have minor accuracy tradeoffs that are beyond the scope of this discussion. Measure each intensity with both the lux meter and the OPT3004 under the window, and compensate using Equation 5. The results are displayed in Figure 9-5, and show that the application accurately reports results very similar to the lux meter.

To validate that the design measures a variety of light sources correctly, despite the large ratio of infrared transmission to visible light transmission of the window, measure the application with a halogen bulb and an incandescent bulb. Use the physical location and light attenuation procedures that were used for the fluorescent light. The results are shown in Figure 9-6.

The addition of the dark window changes the results as seen by comparing the results of the same measurement with a window (Figure 9-6) and without a window (Figure 7-4). Even after the expected change, the performance is still good. All data are both within 15% of the correct answer, and within 15% of the other bulb measurements.

Results can vary at different angles of light because the OPT3004 does not match the lux meter at all angles of light.

If the measurement variation between the light sources is not acceptable, choose a different window that has a closer ratio of visible light transmission to infrared light transmission.

Figure 9-5 Uncompensated and Compensated Output of the OPT3004 Under a Dark Window Illuminated by Fluorescent Light Source

Figure 9-6 Compensated Output of the OPT3004 Under a Dark Window Illuminated by Fluorescent, Halogen, and Incandescent Light Sources