The combination of intensity and time helps us understand exposure
Calculating light exposure over time, such as lux hours, requires a few key pieces of information. First, we need the light intensity measurement at a point in time, and second, we need the time period over which we are calculating the exposure. Any such calculation requires some assumptions based on the sampling rate. When a sample is taken every 10 - 15 minutes, we don't have second by second data about what the lighting conditions may have been, but we can get close if we average out the illuminance readings over that time.
When we calculate the lux hours of exposure, we start with an hourly average of the illuminance readings. We calculate that average for every hour that is within the requested time range. That value represents the illuminance level for a single hour.
Once we have the average illuminance per hour, we calculate the cumulative exposure by calculating the sum of all the individual hourly averages in the requested time range.
For example, if we have a four hour period like the table below, we would represent that four hour period as 120 lux/hours.
|Hour 1||Hour 2||Hour 3||Hour 4|
|Avg lux: 20||Avg lux: 40||Avg lux: 40||Avg lux: 20|