Consider a small flashlight, preferably one with a narrow beam to reduce one's chances of incurring the wrath of others when in close quarters, as is too easily done with a headlamp or broad source phone light.
I prefer lights with selectable brightness levels and have settled upon a narrow beam version of the "Zebra" brand light that uses a single AA cell. Zebra's brightness levels range from just sufficient for close work with dark adapted eyes to bright enough to spot a wilderness trail at 50 paces - one just holds down the button switch to cycle from dim to bright, releasing at the desired level. The individual levels are customizable, if one wants. Zebras come in axial and side beam versions and include a head strap for when one wants to be hands-off.
Lighter weight and nearly as convenient are single AAA cell lights with 3 fixed levels, there are many of these on-line for ~ $10-15. Look for one with a narrow beam.
Both types can be "locked off" by a slightly loosening their caps, to prevent draining the cells with inadvertent turn-ons.
it's also handy to carry a few "pinch lights" attached to jacket zipper tabs.
1. Their illumination doesn't reveal depth well - because the light source and one's eyes are in close proximity, one doesn't see the shadows behind rocks and roots waiting to trip you, or the curb you're about to step off. In contrast, a light held at waist level or to the side does much better.
2. With a light on one's head, it's too easy to give others an eye-full.