I am looking for a guide to understanding the datasheets, this is for someone who has an interest, but is not fully knowledgeable about electronics, explanation for things such as (and not limited to) thermal resistance, temperature coefficient of voltage, or what the chromacity vs current graphs tell you, reflow soldering characteristics, that sort of thing
Whatcha makin? 
nothing right now, but who knows what the future may hold
I’ll answer a few of your questions…
Thermal resistance (2.5 Degrees C per W, for instance, for an XM-L)…
- This is a function that describes the temperature difference between the actual die (junction) of the LED and the package of the LED. The LED as we think of it is the entire square package with the silicone dome on top of it - but this isn’t really the LED - it’s the carrier for the LED. The actual LED is the square semiconductor die that is on top of the package and under the silicone dome. The temperature of this little slice of wafer is what matters. For a cree XM-L, the thermal resistance between this wafer slice and the outside of the carrier is 2.5 degrees C per watt, meaning that if the LED is driven at 3 amps (which equates to a little under 10 watts), then there will be a (2.5 * 10 = 25) 25 degrees C difference between the outside of the LED package and the actual die.
Temperature Coefficient of voltage…
- Once again, a math function that describes the change in forward voltage that an LED undergoes with changes in die temperature. The voltage required to maintain a given current changes with respect to the LED’s die temperature, and this coefficient describes how it changes. Once again, referencing an XM-L, I believe the value is –3mV per degree C. This means that for every degree C hotter the LED die gets, the Vf of the LED decreases by 3mV (.003V). A 10 degree C rise in temperature would equate to a 30mV (.03V) decrease in Vf to maintain the same current flow.
chromaticity vs current graphs…
- The chromaticity of an LED describes the ‘color’ (for lack of a better simple term) that it produces. This color is not perfectly stable with respect to current (how hard the LED is driven). These graphs describe how that chromaticity (tint/color) changes with respect to the current flowing through the LED.
Reflow soldering charachterics…
- Most LED’s are soldered to the circuit board (star board, or otherwise) using a technique known as reflow soldering. Reflow soldering is accomplished by using a paste (about the consistency of peanut butter) of a mixture of very fine solder balls and solder flux. The paste is applied to the circuit board using a stencil (very similar to silk-screening) to just the areas where solder is wanted. Components (such as LED’s, resistors, capacitors, etc) are placed into this paste, and then the circuit board is baked in an oven until the solder becomes molten. The circuit board is then quickly cooled down and the solder hardens - thus attaching the components to the circuit board. The reflow soldering characteristics describe how the circuit board should be heated and cooled to successfully solder the LED to the circuit board without damaging the LED in the process.
Hope this helps.
PPtk