None of the standard clamp lights work for this purpose as they are all better suited for reading books in bed, or barbecuing at night. If I want to photograph very small subjects at close range, with directed light, I need an articulated, dimmable, very bright LED light source....will I have to build it myself or can I buy one somewhere?
Option one: Buy magnifying glass with illumination, remove the lens and shoot through it.
Option two: Use the ring from above, remove much more parts, and make a mout to a camera (use the screw now dedicated to tripod).
Option three: Do-it-yourself. Make a ring array of LEDs and design the power supply and dimming. Look for articles and recommendations regarding pulse width modulation and rectifiers. If in doubt, or struggle, search through and ask Electrical Engineering here. You can use one type of LEDs, or, use several types - with different spectra, aka "temperatures", and power them separately.
Get a Gorillatorch. I have no affiliation with this product other than it works and that my wife bought two for exactly that purpose. One will suffice but sometimes you want to fill in shadows.
The Gorillatorch seems to exactly fit your description: directed, articulated, dimmable and very bright.