[delineal]

My guess is that when the kids' faces were right up to the light, their subconscious mind was actually doing the triggering because the light change was noticed in their peripheral vision. At my kung fu school, we train ourselves to avoid focusing our vision on the person we're fighting because acute vision is translated/filtered by the conscious mind; the tiny delays caused by the conscious mind are enough to get you killed. Acute->Conscious reaction times are far slower than Peripheral->SubConscious reactions.

You'd probably see similar results in your experiment if you had the kids stand close to the light but focus their vision just outside the perimeter of the light.