And I can think so much more clearly. :thumbsup:

This is why I have that bench supply! I can use it to see what my LED's want to be fed, and buy a power supply that fills that need.

The LM138 is good for higher temps than the 338 (150 C. vs, 125 C.) so I'll use those. Found some real sporty dedicated heatsinks for the TO-3 package. My driver will look like the Batmobile, or perhaps the Nautilus (esp. if I do any plumbing! )

So, Weezard, my last question, hopefully, before I start buying components for the red circuit, is:

What watt rating to I need for R1 and R2? It seems like folks are using a 5K ohm Radio Shack pot for R2. These are only rated at a half watt. However, I see some devices on your light that look like 7W resistors. How much juice is going through the R1-R2 resistor combo?

Mouser has a 5 watt wirewound pot-style variable resistor for only $4, but only up to 2K ohm. Would you recommend recalculating R1 value and using resistors/pots rated at 5 watts, or are half-watt parts sufficient here? I know the LM138 is going to have to handle some heat, but what about R1 and R2? Are they putting the brakes on any significant current flow, or are they just reference / sense components? And what the heck is a sense resistor, anyway? (Well, that was more than one question, I guess.)
DreadedHermie Reviewed by DreadedHermie on . Calling out to Weezard for LED advice My friend, I've read your stuff here and at Steve F.'s site. I want to build a dedicated flowering lamp using Ledengin 15 watters. (4 reds, 1 blue, and possibly 1 warm white; LM 317's so I can tweak the ratios.) Essentially, a copy of your 4+1 cake pan lamp but built on a 4 x 18" finned heatsink so I can see what's going on under it.) If I were to post my picks for power supply, resistor ratings / values, etc., would you critique and perhaps offer some guidance? I have already purchased Rating: 5