After more use and brightness tweaking, the COB light bars on the Juki TL-2010Q and Kenmore 158 now have 2.2 Ω ballast resistors setting the LED current to 370 mA and 300 mA, respectively:
Changing from 2.0 Ω to 2.2 Ω produces a noticeable decrease in light, so 10% steps around 2 Ω seem to be about the right increment. The COB LED strips claim 6 W at 12 V = 500 mA nominal, so they’re running well under the spec.
Given that cheap 1% metal film resistor assortments use E6 or E12 value steps, at best, we may need two resistors in parallel for the next adjustments.
The Smell of Molten Projects in the Morning 