You may not have noticed the distribution of sunlight in your living room before you installed hardwood flooring, but you're likely to notice it after. The ultraviolet rays from sunlight lighten wood, and the pattern of incident sunlight mapped on the floor is most visible when the sun isn't out. The best strategy is to avoid fading with strategic placement of furniture and rugs, because, once it happens, your options for fixing it are limited.
Strategies for Blending
If you notice the fading before it has become severe, you have more options for correcting it without resorting to sanding and refinishing, which is the ultimate cure. You can try rearranging furniture and rugs to protect the faded areas and expose the darker ones to sunlight. You may also have some success with dark paste wax, spreading more on the faded areas than on the dark ones and buffing it with a floor buffer. If you have more than one window, you may be able to control incident sunlight so that the entire floor fades to a uniform color.
When a floor finish needs restoration, you can often do it by sanding the floor with a floor buffer and sanding screen -- a process called screening -- and then recoating the floor with a clear finish. If you choose to do this, you can darken the faded part of the floor by adding pigment to the first coat of clear finish and spreading this glaze selectively. You must take care to feather the edges of the glaze to avoid discrete lines of color. Protect the glaze by giving the entire floor at least two clear topcoats. You can add a small amount of pigment to one of these coats to increase color uniformity.
If parts of your floor have been in direct sunlight for many years, you may have no better alternative than to sand off the finish and restain the floor. This is a good opportunity to take care of other defects, such as filling gaps and resetting loose boards. Even after you sand off the finish, the colors of the floorboards will be different, and bleaching the darker wood is one way to achieve uniformity. Use a two-part peroxide bleach to do this. It removes all the natural color from wood and must be used with care. You'll have to stain the wood after using it.
Staining and Finishing
Whether or not you bleach the wood, a stain will harmonize the faded and unfaded sections. You can choose a dye or pigment stain. Dyes penetrate more deeply, and give the most even color when sprayed. You can brush a pigment stain -- which is the type most readily available at hardware stores -- and wipe off the excess with a rag. If the color variations are still noticeable, apply a glaze after sealing the floor with sealer or the first coat of finish. Keep in mind that, while it provides more color masking, it also darkens the floor even more.