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Comment by tomcam | Hacker News Reader

> Michael Strano, professor of chemical engineering at MIT and the senior author of the study, said: 'The vision is to make a plant that will function as a desk lamp — a lamp that you don't have to plug in. The light is ultimately powered by the energy metabolism of the plant itself. Our work very seriously opens up the doorway to streetlamps that are nothing but treated trees, and to indirect lighting around homes.'

Someone help me... I can’t make the numbers work. How can you create plants with enough energy to provide light to read or make your neighborhood safer without sharply increasing their food supply & metabolism? They’d have to photosynthesize vastly more than they do already.

Also those pictures, if genuine (and I don’t think the picture of the tree is) are definitely long exposures.

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Sunlight is about 1000W/m^2. The efficiency of photosynthesis is about 0.2% https://en.wikipedia.org/wiki/Photosynthetic_efficiency

So assuming a 100% efficiency in the conversion of the products of the photosynthesis to light, a 12h+12h light/dark cicle, 100% canopy coverage, ignoring the branches, ignoring that plants need energy for other activities and ignoring that the plant will release 1/2 of the light to the sky instead of to the floor, we get 2W/m^2 for illumination at night.

For a 3mx3m room (10ftx10ft), I'm happy with a 18W LED lamp, and streets are usually darker. (I can't find the official recommendation.)

I'm ignoring a lot of inefficiency sources, so assuming a 100% efficiency after photosynthesis is too optimistic. Organic reactions are usually far from 100% efficiency. I think that a 10% is still optimistic, but it's difficult to give an accurate estimation.

So I think it's not ruled out by the laws of physics, but I don't expect it to be viable as a street illumination method. (On the scale from 1 to Nessie, I'd rate it as Yeti.)

That sounds like a figure that reflects how little energy a plant needs. Becoming an active light source requires more energy than the evolved requirements of plant life. So you have to engineer the whole cycle into the plant.

That is likely the primary issue. Same with a bunch of cool sci-fi things you can do with gene editing in other organisms.

Most organisms are exceedingly energy efficient. [Build me an humanoid-like robot with all its attendant capabilities that can be powered on 2000 calories of snickers bars and apples...]

In order for these things to put of the kind of wattage we're familiar with even in a candle, you'd have to be feeding those plants some really crazy food (not what they usually do), or be charging them up with some super crazy laser (kinda defeats the point of a bio-light).

However, it's still super cool. And you could probably find all sorts of ways to actually charge up a plant in the long run, and as technology matures. Maybe have a whole 'forest' providing energy to a single 'lamp', or be able to provide some direct reservoir of maple syrup the plants can tap into for fuel, or store up energy over a few days for a few hours of light. The energy can come from somewhere else, but it does have to come form somewhere.

But yep - there are some basic laws of physics around energy expenditures that need to be taken into account here.

Plants can't grow LEDs?

Daylight is about 10k times brighter than twilight, so the plants would not need to output much energy compared with what they get during the day. The human eye is non-linear.

https://www.engineeringtoolbox.com/light-level-rooms-d_708.h...

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