2 Light Source Detection

Every light source has a unique emission spectrum, and the characteristics of these spectra can depend on the source that is producing the light. For example, an incandescent light bulb produces a spectrum with higher content in the NIR region than an LED light bulb. Focusing on the intensity of ambient and NIR light allows distinctions to be made between various sources. The OPT4003-Q1 NIR channel is crucial in making this determination, since it is only sensitive to wavelengths between 800 nm and 1000 nm. Additionally, the visible channel of the OPT4003-Q1 has excellent NIR rejection and ensures that the spectral response closely matches the human eye. The excellent IR light rejection of the visible channel and visible light rejection of the NIR channel prevents interference between channel measurements. Coupled with the superior sensitivity of these channels, the unique architecture of the OPT4003-Q1 enables reliable light source detection.

Figure 2-1 OPT4003-Q1 Typical Application Diagram

Channel 0 (visible light) and channel 1 (NIR) of the OPT4003-Q1 report ADC codes proportional to the measured light levels. Calculating a ratio of the channel 0 to channel 1 measurements can create a value that is unique to a given light source type. This calculation is shown in Equation 1.

It is expected that LED sources can have similar ratios to each other, and that these ratios can be different from other source types. A measured LED ratio should be much higher than an incandescent ratio, since LED light sources do not produce content in the NIR region. As a result, the visible light measurement can be much larger than the NIR measurement. Refer to Section 5 for more detailed information about the spectra of common light sources.

For more detailed information on device measurements and register structure, please refer to the OPT4003-Q1 data sheet.