Just to clear up a little misconception created by the optics industry. Scopes do not "gather light". The amount of light that gets through to glass (which is naturally reflective) and to your eye depends on a number of factors, but none of them actually pull in photons.
1. The quality, or lack of impurities in the glass. Lead, and arsenic are added to lower end glass to help remove impurities but leave behind traces of their presence and degrade light transmission and image quality. It's a quick and dirty way to make some serviceable glass, but it's definitely low end. Glass that is allowed to cool very slowly (takes time and time = $$) is better. Nothing added, impurities come out naturally. Glass quality is graded like a diamond. Less impurities = higher $$$. There's really no bargain in glass.
2. Quality of coatings. Since glass naturally wants to reflect light, coatings must be added to allow light to pass through. A number of factors will affect quality of image and light transmission here. First off is the obvious, quality of coatings. Phase coated, etc and terms thrown around but not understood by many. The stupid "ruby lens" coating that tasco used to use was purely a marketing gimmick. Anyway, the quality of the coatings, number of layers, and surfaces coated will affect light transmission greatly. "Multi-Coated, Fully Multi-Coated" all mean something a little different. Multi-coated simply means that the lenses are at least multi-layer coated to reduce reflection. This does not tell you anything about the quality of the coatings though. Fully multi-coated tells you that BOTH sides of the lenses are coated (usually done on slightly higher end optics). This prevents scatter as the light leaves the lens and helps to focus it on the next lens in the tube. Again, this gives no indication of quality.
3. Tube construction. Obviously light needs to be directed down the tube of the optic with an extreme amount of precision to avoid losing those photons. A misaligned lens will affect focus and brightness. Better components, a higher grade of accuracy when milling, and more precisely cut lenses will help to reduce light loss. Again, this takes money.
4. Objective lens size. Yes, a larger objective lens provides more surface area for light, but the human adult pupil can only dialate to about 5mm maximum. If you look at the exit pupil diameter of a 50mm scope, that's 5mm. Anymore light than that, and it is not visible, it's projected around the outside of the pupil. This is why a 50mm Tasco is less bright and clear than a 40mm Nikon..the previously mentioned factors concerning light transmission. More hits the lens with the Tasco, but less makes it through. The biggest advantage to a larger objective lens size is FOV (field of view). As power increases, FOV decreases, a larger objective lens helps to compensate.
Moral of the story, $$$ is about the best indication of quality in optics. Marketing buzzwords don't mean anything. Look through the scope, and make comparisons in low light.