LED-sandwiches. What and why?

[Another-Nocturn]

Hey guys. I am trying to learn a bit about Cree-style LEDs and have a few questions



Aside from giving the LED big solder points, what is the purpose of the star?

Doesn't the star present an unwanted layer of thermal insulation between the emitter and the heat-sink plate?

What about thermal paste... Does it need to be placed between the led and star? How about between the star and the heat sink?

What do I need to know to match a driver with an emitter?

What are the defining characteristics between those LEDs that make crazy beams 1 mile into the sky from those only give enough light to see whats in front of you. (Is the same hardware with much higher voltages?)

About reflectors.. I'd like to create my own in a CAD environment. Where can't I find a good guide to recreating the right shape?

Many thanks in advance

 

[CKOD]

The LED is soldered to the star, a joint though metal to the metal PCB is better than it just being mushed up lightly against a heatsink with some thermal grease there.

the star also provides electrical insulation so emitters like the SSC P7 that have a non-isolated base can be used. For a single LED its not ideal,(ideal being a $$copper$$ heatsink that you put on a hot plate, heat up and solder the led to a mounting post, and then attach leads.) But if you need to isolate the bases from each other its the best way.

You should have thermal paste at every thermal junction you make, between the star and the heatsink, between the heasink and the body.. yeah it'll be messy, bring q-tips and 90% rubbing alcohol

for matching an emitter and driver you need to know:
1) Current limits of LED and your desired current
2) operating voltage of LED (or LED string)
3) Your battery voltage

from there find a driver that will take your battery voltage and has a suitable current and voltage for your LED/string

As far as getting a far throw, from what Ive gathered so far (I.e. not an expert here) you want a LED with a high output density (Lumens per square mm), and aspheric lens's seem popular, though I'll have to defer to the experts.

I wont touch reflector design other then that plotting out what you want for a parabolic design seems easy enough
http://www.candlepowerforums.com/vb/showpost.php?p=3107500&postcount=11