Ultraviolet light is ubiquitous throughout the geological history of Earth. It drives photochemistry and can affect surface environments and organisms. It is an important source of chemical energy that can, in the right circumstances, be harnessed for prebiotic synthesis. When aqueous photochemistry has been explored in the lab, the source of ultraviolet light is often discrete, providing light at a single wavelength. The young Sun, on the other hand, is a broadband ultraviolet source, providing light to surface environments over a wide range of wavelengths. I review how a broadband laboratory source that approximates the ultraviolet spectrum of the young sun affects the rates and yields of various chemical reactions relevant for prebiotic synthesis of life’s building blocks. I then discuss how this broadband source can be used to explore prebiotic and abiotic environments on early Earth and Mars, and in the clouds of Venus today.