A light illuminating element including a transparent closed casing, an exciting gas, a first exciting coating, and a first dielectric multi-layer long-pass filter is provided. The transparent closed casing has a first inner side, a second inner side, a first outer side corresponding to the first inner side, and a second outer side corresponding to the second inner side. The exciting gas is disposed inside the transparent closed casing, and suitable for providing an ultraviolet light. The first exciting coating is disposed on the first inner side or the first outer side, and is suitable for absorbing the ultraviolet light to provide a visible light. The first dielectric multi-layer long-pass filter is disposed on the second inner side or the second outer side, and suitable for reflecting the ultraviolet light and allowing the visible light to pass through.