How quickly are plants able to sense changes in light intensity? Evidently due to the process of photosynthesis, plants are able to "sense" light (as demonstrated by the phototropic response). My question is, how quickly are plants able to perceive changes in light intensity? I.e. if there is a strong light shining on a plant, and at t=0 the light is switched off, is there some delay τd before the plant exhibits a response to the change in light intensity?

The delay for UVR8 photoactivation seems to be in the range of picoseconds depending on the wavelength:

> Global analysis in terms of a model of parallel decaying components indicated four lifetimes of 14.7 ps, 370 ps, 1.9 ns, and 5.9 ns.

![Time resolved uorescence of the UVR8 dimer. \(A\)](

> The photodynamics of the Trp ensemble in UVR8 can be summarized as illustrated in Figure 5B. We observe excited state decay in the few-hundred- picoseconds to nanoseconds time domain to the triplet intermediate U460.

![Tentative photocycle of UVR8
photoactivation as observed in vitro.](

For a better understanding of photoactivation mechanism times, you can read the following article:

Proton-Coupled Electron Transfer Constitutes the Photoactivation Mechanism of the Plant Photoreceptor UVR8 Journal of the American Chemical Society 137(25) · May 2015