Let me expand on what Mike is trying to say. Three chip reflective LCD projectors such as the Sonys and the JVCs pass the light through a polarizer before it hits the chip and after it hits the chip (when it reflects back off the chip. The JVCs keep the polarizers all in the same orientation. That means the red, green, and blue light being emitted from the projector is polarized in the same direction. When this nicely polarized light hits the screen, it will depolarize due to the screen material and its coating unless the materials and coatings are designed not to scatter the otherwise coherent light. So called silver screens which use aluminum reflect a lot of the polarized light off the screen coherently although some of the light is depolarized or made non coherent. No cheap shots by mean about less than fully coherent posts.
Of course the more err silver a screen is the worse it is for 2D. Stewart 3D fabric is a silver screen but it is not as silver as Stewart 5D. It is intended as a 2D/3D screen while 5D is intended only for 3D. Stewart Fire Hawk LS (quite different from Fire Hawk G4) has more gain than FH G4 (1.25 vs 1.1), needs a minimum throw however of 1.6 times screen width to avoid hot spotting but has a very high polarization extinction ratio. A lot of the light bouncing off it remains coherent. Ta DA. Since the JVCs' polarizers are all oriented the same way, if your 3D glasses have polarizer slits oriented the same way as the polarized light bouncing of the screen, the glasses will filter out less light in totally repolarizing the light hitting them. That's what active 3D glasses do. They have fixed slits in both lenses to repolarize the light which in most application is non coherent light bouncing off the screen. This repolarization throws away a large amount of the light bouncing off the screen allowing only the part of the non coherent light that is aligned with its slits to pass. The active part of the glasses is a second polarizer that rotates so to speak (actually orientates its crystals be perpendicular to the slits) to block almost all of the light from passing that lens. If the light hitting the screen and bouncing off it is polarized the same direction as the fixed polarizers in the glasses, one loses a lot less light due to the fixed polarizer in each glass lens. Ergo if and only if your screen maintains a significant amount of polarized light hitting it (most screens do not and that most likely includes yours, sorry) and if your projector orientates the fixed polarizers in it all in the same direction, you will benefit from selecting glasses with matching slits. If you were paying attention, you will note that I did not use Sony as an example. The Sonys do not orientate their chips in the same direction. Without violating proprietary agreements, one of the polarizers in the Sony is orientated 90 degrees from the other two. So if your screen retains a high degree of polarization, matching the slits to the two colors with the same orientation will allow more of two colors to pass and less of the third screwing up the color balance. You can do a 3D calibration but there will be considerably more light loss because of the miss orientation of the third. The best solution here is to get glasses with their slits orientated at 45 degrees, so that no colors are differently treated orientation wise.
Remember there is no perfect screen material for both 2D and 3D. High gain screens (all of them including Da-lite HP are less than ideal for 2D image quality but do give the benefit of having enough light to make you happy (given the right set up). And the extra light is really needed for 3D illumination. The best screen material in my opinion is Studeotec 100 or Snomatt 100 (the same materials) by Stewart. But you need a black pit room because the material has a very wide half angle (and I don't just mean your ability to control ambient light, I also mean your ability to eliminate light bouncing of the walls, ceiling, and floor coming from the light bouncing of the screen. Then your screen must have enough lumens to adequately light your chose screen size. For me with my Sony VPL-VW1000ES, this means at most a 123 inch D 1.78. For 3D, even my 110" D 1.78 is rather dim but is watchable.