You’re probably aware that plants need light to grow. But did you know that photosynthesis is enhanced by certain waves of the light spectrum – like blue, for instance? The bank HSBC has pledged to reduce its environmental impact and help its clients do the same. In order to communicate the initiative, the bank and its agency Wunderman Thompson created billboards with blue backlighting, and installed them right next to the rare green spaces in Manhattan. So while talking about sustainability, the bank also shed some growth-giving light on urban plants. A rare example of posters that contributed something life-enhancing to the cityscape.