In observing with a telescope at night, you need to adapt your eye to the dark environment so that you can perceive a faint celestial object in the field of view of your telescope’s eyepiece. The eye will become adapted to night vision as the pupil is fully opened. However, you may occasionally want to check with a celestial map in the dark or you may need to illuminate around your hands to operate the telescope, a camera and so on. In such a case a white-lit flashlight contracts the pupil and you will have to wait a while until the eye accommodate to the dark again.

The Night Vision Light app helps to hold your night vision in the dark by simply turning the screen of your smart phone into a red-lit flashlight. The illumination of the red light can be adjusted to brighter or dimmer by swiping up or down on the screen. The setting of the brightness is saved for next time use.