All lights are applied deferred in Unreal Engine 4, as opposed to the forward lighting path used in Unreal Engine 3. Materials write out their attributes into the GBuffers, and lighting passes read in the per-pixel material properties and perform lighting with them.
There are three lighting paths in UE4:
Fully dynamic - with Movable Lights
Partially static - with Stationary Lights
Fully static - with Static Lights
Translucency is lit and shaded in a single forward pass to guarantee correct blending with other translucency, which is not possible with multipass lighting techniques.
Translucency can cast shadows onto the opaque world and onto itself and other lit translucency.
https://lh4.googleusercontent.com/oSofFg5UiBQD2uu8nn9qMpPsrNF3LKWRG7k2hkQsRui9UtevDdJU1t0d6q4kT206FAXmDm039DeRYBgMpfP1SGADw0CL5zJowkOwq-BKJ7dP9zKltTolS81_33XNsbxexQ
Materials have a shading model (MLM_Subsurface) for things like wax or jade or ice which are opaque, but in which lighting scatters inside.
https://lh6.googleusercontent.com/WoMprLLHoMBUplirkJYHGBP8YvVAIeQFMRL8VDpgxvD-kulwsxlUk6gbjZE05MqRGIXW08xg29SL-fSzMh7BTizkX22-QGDORXAYeuB83s2kttpqzDVmnxW3g0YVUreFqQ
Particles using GPU instead of CPU, allowing for hundred of thousands of particles.
https://lh5.googleusercontent.com/DrUfhTACPY_rKWWIoHK_6DkxUSS-laYhjQghJHgBIhZRk_SwysjvLfki7XwC-Ma4GjMZSvzHuXc8zI_IUCn2fZ5mavX608Q-jcalCr5S9wRMS7B9BlH5bmAF5IIgzjrsHQ
Grid of vectors (can be placed as an actor in the world) that influences the motion of particles that enter the field, creating cool effects.
https://lh6.googleusercontent.com/EN-mSVdI2kPYxIDXPRqaWwx-zQ3QmdsdufgQsRP06zPjSj6IvEgBtEcxoOnFTxbQmtbsEsVbfJpdTYpNwhx32fBFrUW8pTQd0mkz8aBLBUFnHdhnaUuz1vgQsg9HFqeHkA