Fig. 1

Adaptation of a mat of needles to varying light conditions: PRI and light conditions indicated by the reflected radiance at 570 nm [L(570), in W m⁻² nm⁻¹ sr⁻¹]. The letters (a, b, c, d) identify irradiation transitions plotted in Fig. 2: a, c are high → low transitions and b, d low → high transitions