In an embodiment, an illuminating device includes a light source, a light source control unit, an estimation unit, a first calculating unit, and a second calculating unit. The light source includes light emitters, each having a different spectral distribution. The light source control unit determines an emission intensity of each of the light emitters. The estimation unit estimates a spectral reflectivity of an object. The first calculating unit calculates a first evaluation value, indicating an adequacy of a color of the object visually perceived, based on the spectral distributions and the spectral reflectivity. The second calculating unit calculates a second evaluation value, indicating how much an influence is given by the illuminating light to factors other than a visual sense. The light source control unit determines the emission intensities by which the first evaluation value and the second evaluation value satisfy a restraint condition determined beforehand.
