Glare, not brightness, is why your yard feels dark

On a survey night we ask people to stand at their back door with every light on and tell us what they can see. The answer is usually the lights, the ground right under them, and nothing else.

Your eyes set themselves by the brightest thing in view

A bare floodlight in the corner of your eye closes your pupils down and scatters light inside your eyes, like low sun on a dirty windscreen. Lighting engineers call the scatter veiling glare. Everything darker than the pool of light, the gate, the path, the sky, drops out of sight.

Full dark adaptation takes your eyes about 20 to 30 minutes. One glance at an unshielded light undoes much of it.

A shielded light changes what you see, not the sky

At High Shield Farm our meter read 21.62 mag/arcsec² at the zenith before the refit and 21.62 after. The sky did not change. With the bright sources out of sight, the number of stars you can see from the yard went from about 190 to about 3,680, and the gate came back too.

What to check at your own door

Stand where you usually walk. If you can see the bulb or the bright lens of a fitting from there, it is glaring at you. Aim it down, shield it, or ask us to look.