Agilaire is planning to expand Version 2 of the ADVP to include time-specific rules. For Version 1 of AirVision, Agilaire recommends using the Math Pack function in the data logger to use HRDAY() to determine the hour of the day, daytime, nighttime, etc. It is also possible to use the JULDAY() function in an equation to add a seasonal adjustment factor to HRDAY(), or to directly calculate sunrise/sunset.

For example, you could go to http://www.arachnoid.com/lutusp/sunrise/, put in your location, and get a table of sunrise and sunset times. (You will need to know your latitude and longitude before you can generate the table). In Excel, you can use a graph trendline to develop a Math Pack equation to calculate sunrise and sunset times for any given day. For Knoxville, TN, the equation might look like:

SUNSET = 5E-09*JDAY()^3 - 6E-06*JDAY^2 + 0.0015*JDAY() + 0.7102

SUNRISE = 3E-06*JDAY^2 - 0.0012*JDAY + 0.3466

TIME = HRDAY() + MINHR() / 60

You can then add conditions to determine day/night conditions, such as illustrated below in Figure 6-4:


Figure 6-4 Adding conditions to determine day/night

Another condition for TIME < SUNSET can be added as well.