I only check my observation window at night. I use an led flashlight without issue. My Texas bees are on the defensive side so even checking the window during the day results in 2 or 3 bees sternly investigating me requiring me to use gear to feel comfortable. So I do my quick window checks at night with a light and they don't mind.
Patricia, we use flashlights through our observation windows almost every day, and knock wood, it hasn't been a problem. I find it really useful to see if the "floor" of each hive is clean, and to peak a little deeper between the combs.
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