Blocks alternate between being visible and invisible. Many objects that are transparent to visible light absorb UV. Wavelengths in audible sound are much longer than those in visible light. White light is a combination of lights of different wavelengths in the visible spectrum. Light outside the visible band does not contribute. Many example of hidden treasures guarded by visible or invisible supernatural powers. Other stimuli include the electromagnetic radiation from visible light. Sunglasses offer protection against excessive exposure to light, including its visible and invisible components. The other dihalides decompose on exposure to ultraviolet or visible light, especially the diiodide. Many other fluorescent emissions are known in spectral bands other than visible light. A rendered image can be understood in terms of a number of visible features. Electromagnetic radiation of wavelengths other than visible light were discovered in the early 19th century. Alphabets may exist in forms other than visible symbols on a surface. Work on achieving similar results with visible light is in progress. Chameleons can see in both visible and ultraviolet light.