Whether we're five or seventy-five, all of us like the reassuring glow of a night-light. When something goes bump in the night and awakens us, the small, steady illumination of a night light offers comfort and companionship amidst the big, burly darkness.

Since we grown-ups are usually less than upfront about our still scared-of-the-dark queasiness, we try to disguise our security-blanket night-lights. Why do you think some of these plug-in air fresheners glow in the dark? Some light switch plates and light-switches stay illuminated after being turned off. Have you seen advertised the glow-in-the-dark toilet seat cover to guide us to the right spot at 2 AM?

In the boy's bathroom at our house, night-light duty is taken up by an unusual source of illumination. During daylight it looks stra…