“Light has always been my favorite building material,” says architect Steven Holl. At his new Maggie’s Cancer Caring Center at Barts Hospital in London, light does seem to assume near-tangible properties. Commissioned by a charity that has created more than 20 such freestanding centers designed around the UK by top architects, the facility offers cancer patients and their families practical and emotional support. This center uses carefully moderated illumination to draw in those who feel anxious, to lift their mood and foster intimate conversations. “This small building is important because it can change the way people feel at a difficult time,” says Holl. “Light is essential in doing that.”