Holographic optical elements are utilized in daylighting systems as light directing elements. The holograms can be fabricated on thin foils which are laminated between glass panes. The function of the holograms is limited by dispersion. Especially for large angles of incidence only a small portion of the solar spectrum is diffracted by a single hologram. Thus the redirected sunlight changes color. In this paper we show how the color changes can be minimized by using a stack of volume holograms. Each hologram diffracts a different portion of the solar spectrum into the same direction. The diffracted waves are superimposed in order to generate white light according to the additive color theory. The case of two holograms operating in the blue and red portion of the visible spectrum is analyzed theoretically and realized experimentally. Measurements of the diffraction efficiency as a function of wavelength are presented for different angles of incidence. From these measurements the color performance and the angular sensitivity of the stack is inferred.
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