The OPT4001 has an automatic full-scale-range setting mode that eliminates the need for a user to predict and set the best range for the device. This mode is entered when register RANGE is set to 0xC. The device determines the appropriate full-scale range to take the measurement based on a combination of current lighting conditions and the previous measurement.

If a measurement is towards the low side of full-scale, then the full-scale range is decreased by one or two settings for the next measurement. If a measurement is towards the upper side of full-scale, the full-scale range is increased by one setting for the next measurement.

If the measurement exceeds the full-scale range, resulting from a fast increasing optical transient event, then the current measurement is aborted. This invalid measurement is not reported. If the scale is not at the maximum, then the device increases the scale by one step and a new measurement is retaken with that scale. Therefore, during a fast increasing optical transient in this mode, a measurement can possibly take longer to complete and report than indicated by the configuration register CONVERSION_TIME.

TI highly recommends to use this feature, since the device selects the best range setting based on lighting condition. However, there is an option to manually set the range. Setting the range manually turns off the automatic full-scale selection logic and the device operates for a particular range setting.