Blue lights fill room of house in rural Texas before abruptly vanishing

When I was a child each year my family drove southwest from Dallas to Central Texas, where my father shared a hunting lease on a ranch several miles northwest of Fredericksburg in the Texas Hill Country.
My father is an engineer and an enthusiastic deer hunter, and that year, like most, we came to Fredericksburg at Thanksgiving to hunt deer and turkey. We drove a camper and parked it in front of the old ranch house where I bunked with my father. My mother and two younger brothers slept in the RV. The rustic and less comfortable house, built by German settlers near the end of the 19th c., was situated near a windmill, a sheep shed, water tanks and cattle troughs.
One night my father and I turn out the lights to go to bed.  We were settled in the house, miles from any highway or road, and approachable only by way of a narrow limestone trail cut through sharp grass, oak brush, and scrub.  It was a clear, cool night with no storm activity. We unrolled sleeping bags over the beds.  My father’s rifle rested in a corner.
We had turned out the lights around 10 pm.  My father noticed something after I had closed my eyes and asked me what I saw through the front windows.
A dim blue light entered through a north window, and increased its brightness until the room was cast in a luminous blue.  The light continued through the window a few moments before abruptly shifting positions to a west window.  The room remained saturated in bright blue. Neither of us moved. The light then vanished suddenly after less than a minute.
We couldn’t sleep after the light left us, and we talked about what we had seen for half an hour or so before finally falling asleep.  Next morning we resumed the conversation about the lights. My mother and brothers had nothing to report, sleeping soundly through the night.  
The event has been lodged in family lore all these years.
Witness indicates that the date of the sighting is approximate.  PD