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Comment by wcoenen | Hacker News Reader

> Now lets say blue light delivers only 80 units of energy. When that same cloud passes over, 80 * 75% = 60 units of energy, or a drop of 20 units. So, if your process is sensitive to changes in absolute energy, you would rather have a swing of 20 units for every passing cloud than a swing of 25 units.

That's not exactly it. The idea is that the blue light absorption can be tuned (presumably by shifting the absorbed wavelengths by a few nanometer) to compensate for external changes. So if the overall light intensity drops 1%, the system responds by shifting the absorbed spectrum to get 1% more power.

This only works in parts of the solar spectrum where power varies sufficiently versus wavelength, hence the preference for blue and red.

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Ahh I get it. Maybe the leaves even actually change colour when shaded, but our eyes just aren't sensitive enough?

I'm confused though -- how can the plant possibly shift this?

Biological light harvesting complexes[1] act as an antenna network. I guess the shape and other properties of such a complex change depending on conditions.

The paper doesn't really try to explain the biological tuning mechanism. Instead, they created a model of an antenna network capable of tuning. As in, this model had a bunch of parameters describing how it captured light and tuned. Then if they optimized those parameters for stability given the light spectra that different plants are exposed to, they found that their model would reproduce the actual absorption spectra of those plants. This strongly suggest that the plants have done the same optimization by evolution.

[1] https://en.wikipedia.org/wiki/Light-harvesting_complexes_of_...

And on what timescales does this timing occur? Are we talking seconds? Or days, i.e. accomplished by growing different structures?

FWIW, hardening seedlings to sunlight from a greenhouse is all about switching their spectrum, and it takes 3 to 7 days depending on what plant you're talking about. Gardener's rule of thumb. 4/6/8hr exposure etc.

I wonder if anyone has used RGB LEDs and tormented plants with short cycle color changes yet? There's much anecdata and debate over spectrum vs efficiency in indoor gardening, but it's faded as power density became more obviously dominant, i think.

Yeah, on the orders of days is what I'd expect. So if that's right, then what kind of meaningful tuning are talking about for plants? On the order of days you can simple grow more or less of the green chlorophyll; is that not tuning enough?

Near instantaneous. In the paper it is described as "noise-cancelling".

(waves hands) proteins (or something)

Interesting but why would it not apply the same shifting within the green light spectrum which seems to be quite stabile?

https://d2r55xnwy6nx47.cloudfront.net/uploads/2020/07/Plants...

That's kind of the point. The green section is flat - if you vary the frequency by a couple of nm, you do not see a meaningful change in power input.

But the slopes in the red and blue sections allow you to adjust the input power significantly by tweaking slightly the wavelength of the incoming light.

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