On Wednesday, January 27, 2016 at 7:00:07 AM UTC-5, Don Johnstone wrote:

Silver reflective tape, or mirror tape only works in sunshine. Gliders
spent a lot of time in shade, under clouds, and again at the same
level the effect is minimal.

Nothing is going to work from all directions and under all conditions. But some combination would improve the odds.

LED lights for the shade and mirror for sunlight would be complementary.

A forward facing LED strobe is a big payback even though it works on only one axis.