Can A and B use different locations as well as different dates?

Yes, each point is computed completely independently, so a comparison can mix two different dates, two different locations, or both at once.

What happens when one point sits inside polar day or polar night?

When either point has no real sunrise or sunset for that date and location, the comparator reports that condition directly instead of a numeric change, since there is no meaningful daylight duration to subtract.

Daylight Change Comparator

Enter two independent date/location pairs (A and B). See each one's daylight duration and the signed change between them.

Just need one date's daylight duration? See Daylight Duration Calculator.

Worked example

At 40 degrees north latitude, entering December 21 as point A and June 21 as point B reports a large positive minute change, since June has substantially more daylight than December at that latitude. Reverse the two dates, putting June 21 in the A slot and December 21 in the B slot instead, and the exact same magnitude comes back as a negative change, since the comparator always reports B minus A regardless of which date happens to have more daylight.

Common mistakes

Assuming the sign convention runs the other direction. The change reported is always B minus A, so a positive number specifically means B has more daylight than A, not the other way around.
Comparing two points where one sits inside polar day or polar night, then expecting an ordinary numeric result. That condition is reported directly instead of a misleading number.

Limitations

This is an astronomical estimate using the standard NOAA solar equations, not a measurement of actual visible sunlight. If either point has no real sunrise or sunset for its date and location, no numeric change is reported for that comparison.

Frequently asked questions

Can A and B use different locations as well as different dates?: Yes, each point is computed completely independently, so a comparison can mix two different dates, two different locations, or both at once.
What happens when one point sits inside polar day or polar night?: When either point has no real sunrise or sunset for that date and location, the comparator reports that condition directly instead of a numeric change, since there is no meaningful daylight duration to subtract.