The ratio of red and blue light controls various functions of a plant. In the context of aquarium plants, more red light makes them get tall and leggy, more blue light makes them be compact and bushy.

https://gpnmag.com/article/effects-of-blue-light-on-plants/ talks a bit about it in the context of greenhouses and tomatoes, the picture in the middle shows 6 plants grown with wildly different red/blue ratios.

If the balance of the light coming through your solar panel was problematic, you could always filter out some of the overabundant light.

Is that how they know how close to the surface of the water they are?

A blue plastic bag filters most of the spectrum EXCEPT the blue part. Not the other way around. Simple proof: look inside, the light is blue.

I guess the biggest problem for the plant here is that especially the infrared part of the sunlight is very important. Yellow leaves usually mean not enough light. Especially tomatoes need lots of sunlight.

Nope. If the bag looks blue that means it's scattering away blue light while letting the rest through. So it's filtering (out) the blue. OP is right.

No, a blue filter, like a blue plastic bag would let blue pass and absorbe the other colors. That's why if you shine a white light through a blue filter, things look blue on the other side.

Now, some of the blue light is scattered away, and that's why you see the plastic bag itself as blue.

Hang on, so if you shine a white light through a blue filter, the light on the other side looks blue. And the filter itself still looks blue on both sides. But then, where did the non-blue component of the light go?

Converted to heat. What's going on here is a discussion about transmission and transmittance. [1]

[1] https://www.swiftglass.com/blog/key-differences-transmission...

Imagine looking at this blue-transparent bag with a red light, it will appear more opaque.

Just like laser light protection goggles.

If you see blue on BOTH the outside of the bag and the inside, what does that mean? I’ve never thought of this.

It means some blue goes through, some is reflected.

As a guess, perhaps the unfiltered light that gets through goes through a phase change from being reflected. https://en.wikipedia.org/wiki/Reflection_phase_change

That slight colour blockage, or the tint those solar panels have is helpful.

There are two reasons. One, plants grow better under red light. Red light has the highest efficiency for photosynthesis in plants, that why LED grow lights are tuned for certain wavelengths. Plants use blue light to know what direction to grow.

And for a certain category of tints or dyes that are fluorescent, additional red light.

Luminescent solar collectors have an embedded dye with molecules that fluoresce, that give off even more red light.

Example: http://www.soliculture.com/lumo-technology/

Is that why indoor LED growing lights have that purple-ish tint to them? I never knew that. I knew about the red, but never the blue. You're awesome. Thanks so much.

Here's my source material: https://youtu.be/Y1nlQ6bGX4c?t=4018

All of my plants this year have gotten blossom rot, pretty much too late to fix too. No tomatoes for me this year.

Blossom end rot is caused by calcium deficiency. Easiest solution for this is to just crush up egg shells and put them in and on top of the soil. I save my eggshells in a jar in the fridge for a few months prior to planting. It may be too late for this year but should work wonders for you in the future.

I had deformed cumquats from my tree until I started blending egg shells in the spice blender and watering them into the tree base.

Seconded, I would do this with my mom each year in her garden when I was a kid. Works 100% of the time, and it's a non-invasive way to address the issue.

Not always. Sometimes it's because it's too hot at night.