Roller blind, particularly for use as blackout shade

A roller blind particularly for use as a blackout shade, comprising a spring-biased roller bar for mounting at the top of a window opening and a blind rolled on the roller bar, said blind having lateral edges and guide members along the lateral edges, guide rails disposed at both sides of the window opening, the guide rails having tracks for guiding said guide members, said blind further comprising a bottom bar having two ends each having further guide means, said guide rails having guideways for engaging said further guide means, a cord arrangement for controlling the raising and lowering of said blind, said cord arrangement comprising a first cord having one end connected to a fixture arranged at a bottom of a first one of said guide rails and passing therefrom through a part of said guide rail positioned below said bottom bar, through the bottom bar and through a part of the other guide rail positioned above said bottom bar to an opposite end of the first cord, said opposite end being connected to a fixture arranged at a top of the other guide rail, said blind further comprising a brake device mounted in said bottom bar and including a friction member fixed with respect to the bottom bar and having a perimeter in frictional engagement with the first cord, the cord being in engagement with substantially 360.degree. of the perimeter of the friction reversing member to permit the bottom bar to be retained in any arbitrary position against the effect of the spring bias, said cord arrangement further comprising means for tensioning the first cord, said tensioning means being positioned at one of said fixtures.