The optical properties of a novel light modulator consisting of colored particles of N-isopropylacrylamide (NIPAM) gel, a well-known thermoresponsive gel, dispersed in an aqueous poly(vinyl alcohol) solution were examined. The performance of the light modulator was mainly defined by two factors: the NIPAM get properties and device compositions. The NIPAM gel properties included the amount of the volume change, the volume-change temperature, and the pigment concentration in the NIPAM gels. The larger the volume change was of the NIPAM gel particles, the wider the transmittance change became. The color-change temperature was controlled by the manipulation of the volume-change temperature of the NIPAM gels with the addition of sodium dodecyl sulfate (SDS). The volume-change temperature of the NIPAM gels became higher with an increasing concentration of SDS. The pigment concentration also had a significant effect. The higher the pigment concentration was in the NIPAM gels, the wider the breadth of the transmittance changes became. This occurred because, in the case of low pigment concentrations, absorbed water diluted the pigment, and this led to low absorption at each NIPAM gel particle. The properties of light modulation could also be controlled by the composition of the light-modulation layer. The two main parameters were the concentration of the gel particles in the layer and the thickness of the layer. The transmittance of the light modulators decreased as the thickness and/or concentration of the gel particles increased. Light modulators with various colors were obtained with NIPAM gel particles containing pigments of different colors. (c) 2006 Wiley Periodicals, Inc.