When I left work to go home yesterday, I noticed that my '93 Accord's dome
light was on before I even opened the door. After I got in and closed the
door, the light was still on. I checked the switch on the light itself, and
it was in the middle position (light comes on only when a door is open).

Now fearing that my battery may have been drained, I turned the ignition to
"on". After the "lamp test" concluded, the door ajar indicators showed that
one of the passenger doors was open. Turns out that, unbeknownst to me, my
passenger did not close the door tightly when we arrived at work 9 hours
earlier.

As it turned out, the car started with no problem at that time, and today it
was also fine. Which brings me to my question. Is it possible that I (or
should I say, my passenger) still may have shortened the battery's life by
having the dome light continuously on for 9 hours without the car running?
Or is the dome light less taxing on the battery than, say, the headlights
and it will be OK?

The battery is an almost 4-year old Sears DieHard, if that matters.

Thanks in advance for any answers you can provide.