Cyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2] cycloadditions that exploit low-wavelength UV radiation emitted from inefficient medium-pressure Hg lamps. This paper, co authored by Almac’s Megan Smyth and Tom Moody, discusses the development of a modern approach using a high power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous-flow reactor.