For Strips Comfort – the discreet temperature & LUX sensor, Sensative has developed an algorithm for ambient light reporting system that reports in regards to relevance. Instead of having a certain reporting interval, which is the norm, we have decided to focus on changes to bring down the total number of reporting, without losing accuracy & speed when light change happens.
Over the course of a whole day or a whole night, there are long periods of time where there are no significant changes in the lighting conditions; therefore the device reports the same LUX level over and over again. For a sensor that reports every 5 minutes it means that 288 reports are being sent during a 24 hour period. This results in the battery lifetime being affected. For Strips during a day with a normal amount of sunlight only 20 to 30 reports are sent during a 24 hour which is the main reason why a long battery lifetime is possible to achieve.
What Strips Comfort does is it reads the LUX sensor once per minute and makes a decision if it should send a report or not dependent on the difference in reading since last report sent. A new report is sent when the LUX value is double or half of the previous value sent, or if 24 hours have passed since the last reporting.
The human eye sensitivity is logarithmic in the same way as the ear is for sound levels, reacting to a relative change of energy rather than absolute levels. A change with a factor of 2 in light energy (LUX) is a noticeable change for the human eye.
Strips Comfort also has a filtering function to avoid temporary changes (such as headlights passing by) or if a person is passing by and blocking the sensor to trigger a report. The filtering levels are dependent on the mode set – normal or frequent. Normal reporting provides more filtering and frequent reporting has a lighter filtering allowing changes to more quickly pass through.
The graph below is an illustration of the Strips sensor placed on the inside of a window reporting the LUX values of sunlight over a 4 day period of time: