Are controllable, predictable flashes of light in vision usually benign? like every time i look up quickly in dark, i see a small flash at the bottom.

Not always!: Posterior vitreous detachment. This is a situation where the vitreous(jelly) of the eye detaches (not a retinal detachment), it then "crumples" up leaving dots, spots, strands of blurry vitreous; i.e. The "floater". When it pulls away (initially tugs), it causes flashes. You should have an exam to ensure the incident did not tear the retina, which could lead to a retinal detachment.

Photopsia: Or light flashes, are very common symptoms. They occur when the vitreous jelly in the back of the eye shifts and pulls at part of the retina. Usually, once the vitreous separates from the retina, the light flashes resolve. If you develop some floaters or dark shades coming over the vision from the side, then this could be an indication that there is a retinal tear or detachment. See an eye doc.