Regarding LEDs:
Yes, please re-read. The most common usage is a 3W LED, run at 700 mA, so really run about 2.4 Watts.
Interestingly, those 3W LEDs are rated to 1000 mA, with a Vf of 3.5 or so there, so really about 3.5W max.
But to make it more fun, the measurements in the data sheets are done at 350 mA, where it is most efficient.
Marketing... :|
Note that common-practice is changing with the newer XP-G LEDs, they are rated to 1500 mA, so often run at 1050 mA, so about 3.6 Watts.
Running LEDs at max current decreases efficiency, longevity, and can affect color a bit, so under-driving is a good practice.
You can use any power LED you want of course. 1/2W to 100W. Whatever. But there are big trade-offs.
Using 1W will work. You just need more. How many more will depend on lumens/watt, so it is likely more than 3X!
The smaller ones are usually less efficient.
If you use 20W on the other hand, you need less, but now you end up with coverage and spot issues, and/or complex optics,
plus thermal issues.
In general, 3W - 5W is a good sweet spot, which is why most are done that way.
Then there is the question of using optics or not, and in my mind, the most important, trickiest, and often ignored : COLOR.