It's a good decision to replace the incandescent with LED down lights because though LEDs are expensive than incandescent in the first term it will save you a lot of energy as well as money in the long run, as they consumes less energy than the incandescent lights. there might be some case where incandescent will appear to be little brighter than the LED lights but the benefits of using LED outwits the incandescent lights.
As an optometry student, I'm having trouble trying to make sense of your question, and that's because it makes no sense at all. "Bad eyesight" does not affect the "brightness" at your retina; rather, it affects the accuracy with which light rays focus on it. Luminance is controlled by factors such as pupil size, not your prescription. And unless you put a tint in your spectacles, glasses will do nothing to affect "brightness at the retina" at all.
Yes, Yes it does!
NO
Two factors that affect a star's apparent brightness are: 1.) The distance between the Earth and the star 2.) The absolute magnitude (the actual brightness) of the star Hope that helps :P
Yes, it will. The higher the brightness. the less the battery life will be.
How old a star is.
the brightness hurts your eye rods
By definiton, "dark" matter neither emits or absorbs light. Thus, it does not effect the brightness of galaxies.
Distance and intervenng or close celestial bodies
Distance and intervenng or close celestial bodies
Distance and intervenng or close celestial bodies
Distance and intervenng or close celestial bodies