Consider the Boriut headlamps . Both the D10 an the older / bigger (red bull can size ) R2 which has usb and an easy to use micro switch . Also the t1 zanflare lantern or whatever they are calling it now with usb and touch sensitive switch.

Those multi colored /plastic push lights are easy to push for old people with no bones left in their fingers .also lights with motion detection are handy when walking into or out of a room .

The answer is probably a combination of lights vs. one perfect light for grandma .

My Grandmas favorite lights are an original thrunite AAA ti 2 modes in green //because it's tiny bright and ...green .She may not be able to push a small button well but old people can twist the hell out of some stuff (except for a jar). She likes the cheap plastic push light that goes red green blue/? white . I'm hiding the remote control from her .(too many buttons, too confusing)