NOVELTY - The solar reflective fiber (100) having a longitudinal axis, comprises a continuous primary portion (110) having a first refractive index, secondary portions (120) having a second refractive index, which is different from the first refractive index, and a core-shell structure. The primary and secondary portions are arranged to run continuously along a portion of a length of the fiber. The primary portion provides a host medium within which the secondary portions are provided. The primary and secondary portions are arranged to constitute an optimized dielectric mirror structure.    USE - The solar reflective fiber is useful in a fabric, a garment, a building, a roof of a building, a solar concentrator, a lighter-than-aircraft including a blimp and an airship, a fiber reinforced composite material, a fluid injection apparatus and a display apparatus (all claimed).    ADVANTAGE - The solar reflective fiber reduces air conditioning costs of buildings, an amount of energy required to run air conditioning systems and an amount of solar radiation by which a temperature of the aircraft rises, and increases the lifespan of the roof.    DETAILED DESCRIPTION - The solar reflective fiber (100) having a longitudinal axis, comprises a continuous primary portion (110) having a first refractive index, secondary portions (120) having a second refractive index, which is different from the first refractive index, and a core-shell structure. The primary and secondary portions are arranged to run continuously along a portion of a length of the fiber. The primary portion provides a host medium within which the secondary portions are provided. The primary and secondary portions are arranged to constitute an optimized dielectric mirror structure such that a phase of a scattered beams of radiation scattered at respective interfaces between primary and secondary portions interferes constructively with one another to reduce an amount of solar radiation transmitted through the fiber in a spectral range of 300-1800 nm. The secondary portions are provided in the form of tube elements, which are discrete elements, and comprises a fluid-filled void. The tube elements are arranged in concentric rings as viewed along the longitudinal axis of the fiber, and are provided in a spiral-shaped arrangement as viewed along the longitudinal axis of the fiber. The spiral-shaped arrangements as viewed along the longitudinal axis of the fiber are centered about a common axis, and are provided at different angular positions with respect to one another. The common axis is coincident with a longitudinal axis of the fiber through a centroid of a cross-section of the fiber, where the cross-section is a cross-section normal to the longitudinal axis. The primary and secondary portions are arranged such that a trajectory of a beam of light passing through a centre of the fiber along a path normal to the longitudinal axis of the fiber passes through a portion of the primary and secondary portions. A diameter of respective tube elements is a nonlinear and/or linear function of a distance of the tube element from the longitudinal axis of the fiber, and increases and/or decreases as a function of distance from the longitudinal axis. The fiber is coupled to a fluid source, which is arranged to inject first and second fluids into the fiber to introduce the first and second fluids into the fluid-filled void. The first fluid has a value of refractive index within 10% of that of the primary portion. The second fluid has a value of refractive index within 20% from that of the primary portion. A core of the core-shell structure is provided by a colored tertiary portion, and the shell of the core-shell structure is provided by the primary and secondary portions. The primary portion comprises a core portion, and radial spoke portions projecting in a radial direction, and the secondary portions are provided between the respective adjacent spoke portions and tapered along a radial direction. INDEPENDENT CLAIMS are included for:    (1) a display apparatus; and    (2) a fluid injection apparatus.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a fiber.    Fiber (100)    Primary portion (110)    Secondary portions (120)    Elements of outermost ring (125A)    Tube element. (127)