light particles
Light particles are either glowing or illuminating objects, usually very small in size and come in clusters, added to enhance an image or for special effects. (See Danbooru post #7448569, Danbooru post #6228) Normally can be seen along with ray of light coming from a window. (emulating the effect when light struck against dust particles in real life)
Also used for light circles in charging or accumulating power for energy-based weapons, spells and the likes. (See Danbooru post #927612)
Use ashes, powder, debris, or some related tag if the particles do not glow. If it is a considerably large, tag sparkle instead.