would it make sense then to put shade cloth over tomatoes when their fruit is ripening so as to increase the sugar content. or maybe even provide supplemental red lighting.
( please lets not discuss the source of said lighting in this thread )

Hi grizzman,
Flavor preferences for tomatoes goes beyond sweetness of course.
Regarding sweetness, the use of deliberate shade to manipulate the kinds of "sugars" is not likely to give you sweeter results. My reasoning is detailed below.
Regarding supplementing "blue" spectrum - seems of potential use. The proportion that you use may have an upper limit before you inadvertently cause some other side effect.
Genetic characteristic of your tomato variety is a major taste factor; Cherry tomatoes are yet another sub-set capable of even more sweetness.
The measurement of light refraction through the soluble solids, like carbohydrates (sugar) & minerals, in ripe tomatoes let's us compare sweetness; with a scale called Brix.
A higher Brix = more soluble sugar; due to an increase in sucrose (I skip the nuances of different types of sugars). If the plant is in direct sun light then get maximum photosynthetic activity & then sucrose as a result.
In greenhouse tomato cultivation the sheer numbers of fruit yielded is increased by stripping lots of leaves; yet the full size fruit is not particularly sweet. (The varieties grown in commercial greenhouses get selected for assorted reasons.)
When you do the opposite & prune away some fruit, so that there is proportionately more leaf, the end result is sweeter tomatoes.
There is a post of Feb. 16, 09: "Soil, Salt & Tomato Taste" with a video link in the thread I found interesting; on GW Tomato Forum. The greenhouse shown has tomato plants with full leaf cover & sweet fruit.
As for the genetic influence:
there are enzymes determining how any specific tomato variety works with carbon (as in carbohydrate). This means there are different degrees of enzymatic interplay that rule the effectiveness by which the leaf makes carbohydrates, develops sugars & (possibly) even how readily gets it going into the fruit.
In some tomato varieties there is a genetic programed feed back loop; where high soluble solids (Brix) instigate the plant's DNA to put out even more sucrose processing enzymes; so it can get even sweeter. (If the plant has no excess sucrose to work with, because it has not enough leaf area for carbon processing, those extra enzymes stay mute.)
The types of tomatoes with low Brix (sweetness) lack this special genetic capability to go into sucrose over drive.
Lastly, there is evidence that the way to grow the sweetest tomatoes is by the grower manipulating several factors, rather than just vine ripening.
The video I mentioned (in the thread of post above) comes to mind. The Japanese grower gives the following clues to sweet tomatoes:
water restriction (concentrates solubles in fruit), small mature tomato size is from standard seed (genetic predisposition toward ideal enzymes more important than maximizing weight), plenty of leaves (sucrose production) & nigari (mineral concentrate, beyond scope of this post).

That's some good info. Bear in mind the digression on radishes was in regard to partial sunlight under the shade of peppers, though. In case anybody doesn't know, I was the digressor when I said that radishes do well in partial sunlight under the shade of peppers. Anyway, there is a very big difference between partial sunlight and shade. I'm not just playing word games here. They are two entirely different growing conditions and I don't think that radishes would do well in shade. Partial sunlight generally means the plant gets less than 6 and more than 3 hours of sunlight a day. It also normally is accepted to mean afternoon sun coupled with afternoon heat while partial shade generally means the same number of sun hours but only in the morning without the accompanying heat. My radishes get about 4 hours of sun in the afternoon with the sun's current sky position.

With radishes, I will get varying sizes in the spring even in the same generals areas with the same planting times. A radish can be 20% bigger than others just a few inches away or a few may be smaller than their neighbors. So many variables in soil can obviously cause the variation in resulting edibles. The size of my current radishes (partial shade grown under pepper leaves) are quite a bit larger than the first round at the same age (just under 4 weeks). We've had more rain this round, though. I don't believe the size had much to do with the sun at all when talking about the difference between my early spring and current radishes. Also, the radishes I picked yesterday were sweeter than the spring ones, which had a very mild spiciness to them (which I prefer). Not sure if they were really sweeter or if the complete lack of spice just made the sweetness more noticeable. I'm guessing it is probably the latter, in reality.

In a controlled environment where all conditions but that which is studied are the same then I'm sure it would matter. Or, of course, in an indoor environment like hydro. But the reality is that in outdoor soil gardening we do contend with variables that change from one year to the next (which is why many of us are doing indoor hydro, right?). For example, this past month has been a lot cooler than normal. My radishes last year weren't nearly so sweet and I assume it has to do with the heat.

I don't use pro equipment, but the light meters I have show the light intensity as being quite high enough even in shade of the peppers. I have wondered how accurate they really are, though.

All in all, I must admit that I prefer the slightly spicy spring radishes, but my kids and will not even eat them. They have no problem at all with the ones I just pulled, though. And my wife prefers the recent ones. That makes them even more valuable.

Fresh pulled for your viewing. It's my last pepper shaded one. Well, along with the other 4 I just pulled. Didn't put down any more successions in this bed, but I have some growing in a tree shaded spot at my grandfathers, too. Anyway, these are a lot bigger than any others I normally see of the same variety. As far as I'm concerned, the proof is in the pickin's! For those interested, I only use compost and worm castings (from my own worm bin). I do add manure to the compost pile. No other ferts in the soil. This radish is on the northeast facing side of that pepper plant in the pic.

Hi joejr,
Do you think the spring angle of the sun as opposed to the current sun angle might mean the wave lengths your radishes received were different ?
Maybe this time they are sweeter since had more "blue" exposure time.
(Nice planting bed you made to grow in.)

Yeah, that's why I mentioned current sun position. I think it could be a contributing factor. I just don't know how much. Again, there are so many variables I couldn't begin to track what causes what. We've had more rain. I was more diligent with the compost in early spring to make it as nutritious as I could. The earlier radishes had to make do with the fall compost, which I'm sure lost nutrients over winter. Etc. There are probably others I haven't mentioned due to my poor note taking.

On the tomatoes: I am experimenting a bit on tomatoes right now. See my pic in the "Tomatoe Tips" thread. Freeman had mentioned another thread suggesting stripping leaves. I had replied that I was under the impression the leaves determined brix factor. I have plants that are stripped in what I consider a heavy manner and plants that are quite bushy. The stripped plants indeed have faster fruiting and more flower clusters. I'm going to perform the ultimate test at harvest. . . my 6 year old daughter will tell me which ones are better. 6 year olds have much better sweet taste buds than 32 year olds that have smoked (though no longer) and drink way too much coffee. She is a tomato taste expert! I'll call it the Sarah factor. She determined the tastiness of my cherry tomatoes last year in my indoor vs outdoor growing experiments. She spit the indoor cherry tomatoes out, which were grown under artificial light, but seemed to not be able to get enough of the ones grown under sun.

I referenced a thread above, with this video about Nigari & tomato sweetness:
http://www.youtube.com/watch?v=zmXu4dr.R1S8
Nigari has a lot of Magnesium ( & sea water trace minerals) so the role of mineral "salts" is what will discuss.
Metal ions impact the genetic code signal in several ways.
They can stabilize the genetic information coils or torque them out of position, influencing how that genetic program is read . This means that the precise "kick-starter" of a specific protein ( what the gene expresses to be made, in order to start things going) can be influenced by trace minerals.
A deficiency of a vital trace mineral causes too little of the genetic signal "kick-starter".
An excess of a trace mineral can destabilize the configuration of the master code strands & cause a different "kick-starter" protein to be expressed.
As this pertains to Nigari (opposed to NaCl, sodium chloride salt, which increases conductivity to reduce water intake, makes tomato fruit smaller & thus concentrates % of sugar ) the likely sweetness factor to follow is Mg.
Let's scale back up to enzymes.
Tomato fruit uses sucrose, when young, to develop seeds. The sucrose form of sugar will eventually get acted on by sucrose specific enzymes & broken apart into other sugar molecules.
As fruit develops the fructose form of sugar is a byproduct (mature fruits' sugar is in the form of lots of fructose). Here begins a factor of how sweet can things get & it is a dynamic influenced by trace minerals.
On one hand, the fructose building up in the fruit tends to inhibit the very enzymes that specificly break apart sucrose & let the fructose "out" . It is a genetic program & why some tomatoes don't get sweeter than a certain degree.
Yet, on another front, the enzymes that act specificly on fructose act to clear the cell structure (cytosol) where sucrose is made of all that built up fructose. This is a circumstance that, in effect, takes the "lock" off the sucrose enzymes & the result is that sucrose can again get acted on so sucrose's fructose is again let out (ie: fruit gets even sweeter).
Which brings us back to the trace metal ions. There is evidence one of the key sucrose transformational enzymes is Mg++. It is not that this trace mineral is incorporated into the enzyme itself, but what it does.
Previously it was explained how trace mineral "salts" influence a protein structure (peptide) formation to occur. This is the 3 dimensional key refinement that is shaping the event.
In other words, the trace mineral ions rule the bridging that might occur between a protein's amino acid (components that define the type of protein) & this specific geneticly expressed protein's intended receptor site. If no docking is possible by that protein "sent" from the gene then no enzyme goes to work.
Nigari's Mg++ possibly may make tomatoes sweeter through "over-driving" the interplay of the sugar (sucrose & fructose) regulating enzymes, by making both enzyme's bridging phase go quickly .
It may be possible that Nigari's other ++ trace minerals can favorably orientate (twist) the genetic informational strands so that enzyme proteins are produced (expressed) that "hot-wire" some tomato varieties into sugar processing.
In this last case, the unknown ++ trace mineral would work by causing more total production of the actual enzymes that act on sucrose & fructose sugars (as opposed to making these enzymes work faster). This would only be possible in geneticly pre-disposed tomato varieties.
It would be interesting to hear anyone's suggestions on how much & when to use Nigari.

Editing follow-up subtitled "Nigari", more than 1/2 way down.
Paragraph begins : "Which brings us back to the trace metal ions...."
The following sentence structure reads poorly, lacks a modifier & so wrongly says Mg++ is the enzyme.
What was meant to be stated is:
that Mg++ is important to how one of the enzymes that breaks down sucrose works.