put in another fixture
Increasing the wattage of the existing fixture may not solve your problem.

A good rule is a light source every 8 ft of hall length. Using a covered 2 lamp fixture should be fine for 8' ceilings. Sounds like you already have those. If your placement is now 6' from each end then you have about 16 feet of space with no light. If this is correct, you really need 2 more fixtures. If you were planning this from scratch, you needed a light at the top of the stairs, which sounds like you have, and then a source of light every 8 feet or so. When designing a lighting plan I try to plan these to fall in front of closets or other elements that need extra light, if they don't contain their own sources. If you don't have any power source or can't add one for the closet, a battery operated motion fixture could work there. Place it inside the door on the wall next to the door so you can reach it easily. You can just stick your hand in to activate it and turn it off the same way or just let it turn off with the built-in timer. Use the LED ones that stay cool. These are realtively inexpensive. Try LC-LED-480 which is intended for the ceiling if you have room or LC-LED-4835,that works great on the wall. One source is yourlightsite.com. Look under Off the Grid fixures.

Don't change the glass on the fixtures to clear. Clear glass creates a lot of glare and can very uncomfortable unless you use very low wattage bulbs. In your case, this would defeat the purpose. Clear glass and clear light bulbs actually produce less useable light due to the glare factor. Clear light bulbs should only be used for a decorative purpose and always with lower wattage bulbs or with a dimmer. Frosted or white glass will reflect the light in a broader area shielding the light, reducing glare and distracting shadows. Never use clear light bulbs behind white or frosted glass, they produce filament shadow which is very unattractive. I prefer recessed lighting supplemented with wall sconces for halls if this was a new project. In very long hallways I try to include recessed step lights as nightlights. Working with what you have, and purchasing 1 more to match should do the job. Of course you will need to run additional wiring to the new fixtures, but they can all use the same switch, which hopefully is located at the top of the stairs. Just a note: Don't overlook the possibility of using a motion activated switch for the hall lights if the installed switch is not convenient for turning off, once a person goes into the bedroom for the night. It is a lot less expensive that multiple location swtiches, especially working with exisitng structures. If your hall is wide enough, s small demilune table with a portable lamp can also make the hall more inviting and act as a night light when fitted with long lasting energy effiecient bulbs. Hope this helps.

Ginger Rushing, CLC

Would a recessed look too strange with the flush mounts at either end? Would a single recessed give enough light with the other lights 14ft apart? I hate the mushrooms, and trying to avoid it looking like "ceiling acne" as someone on another forum called it. Thanks.

Ginger - we were posting at the same time. The hallway is very narrow, and the only long wall I have to put sconces on is the marriage wall and could be hard to pull wire through (no outlets on it, and the room on other side is a different module (2x 4's back to back alternating so 12" OC, exterior sheathing in between?). I do have full attic above, plywood flooring so we can pull it up, move some insulation and add some lights. Switch at each end of hall, we can break the wire b/t the 2 existing fixtures and add one, but not sure I can add 2 with all the other stuff on the ceiling.

Since I do have the sconce at the top of the stairs, and can add LED to closet, if I can only add 1, should I try to center it between the others, or closer to the one end of the hall that's longer run from stairs? The stairs are 3ft wide, the existing hallway ceiling fixture closest to stairs is 3ft from that, so 6ft from sconce.

I really messed up my guesstimates. The hallway is 23ft long give or take a few inches (only have 20ft tape). One fixture (closest to stairs) is roughly 39" from end of hall, right outside my kids' BR doors. The other is about 17ft away from that one, only 3ft from MBR door. One switch by MBR door, the other b/t DS's door and linen closet.

I don't mind patching the ceiling if it makes sense to move the existing lights in addition to/instead of adding a third.

I do plan on adding an outlet underneath the switches near Ds's door so I can put a nightlight there shining down the stairs (at floor/top step level). I would just put a low-wattage/lumen bulb in the sconce and use that, but don't want to leave the fixture at bottom of stairs on all night. I had also thought about adding rope lighting to the stringer before we finished it out but don't know how hard to would be to wire in a modular (front/back, top/bottom marriage walls). Thanks