The amount of light required to illuminate an entire galaxy is an astronomical scale of measurement. Galaxies are vast collections of stars, gas, dust, and other celestial objects, and their sizes can vary greatly. Therefore, it is challenging to quantify the exact amount of light needed to illuminate an entire galaxy uniformly.
Furthermore, galaxies emit light from various sources, including stars, active galactic nuclei, and nebulae. The total luminosity of a galaxy depends on factors such as its size, composition, star formation rate, and the presence of any particularly bright objects within it.
To give you a sense of the scale involved, let's consider the luminosity of the Milky Way galaxy, which is the galaxy in which our Solar System resides. The Milky Way has an estimated luminosity of around 5 billion (5x10^9) times that of our Sun. This means it emits an enormous amount of light, but it is spread out over its vast expanse.
In order to illuminate an entire galaxy evenly, an immense amount of light would be needed, likely far beyond the capabilities of any current or foreseeable technology. It's important to note that the illumination of a galaxy is not a practical or achievable goal in the same way we would illuminate a small space with artificial lighting. The natural light emitted by the stars within a galaxy is what allows us to observe and study it.