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I decided to make a light module out of 28 LEDs in parallel. Hooked it up to a lab bench. Without constant current regulation, any initial current above 840ma (30ma per LEDs) will result in a (very gradual) thermal runaway where the module start to pull more and more current and heat up more until it would presumably burn out. On the first try, I initially set the current at 1.4A, and it rose up to almost 1.6A within 10 minutes.

Granted, these LEDs are packed fairly tightly together and thus complicating the thermal problem. I'd say, if you want to run this LED on a long term, you shouldn't be running this at 35ma (per LED) or more without airflow.

With 840ma starting current, the final current stabilized at 900ma.