What's Tj mean? Seen it used in convo. & i'd like to always understand.
Tj is the junction temp measured where the dies are connected, as photon said above it is the closest real measurement to diode temp. as opposed to more easily measured Tc, case temp of the chip which is measured on the chip itself. so theres thermal resistance from the diodes to the case, and then from the case to the heatsink
here is a page which explains Tj,Tc, Rj-c, etc really well
http://www.led-heatsink.com/LED_heat_sink_calculation_simulation_thermal_design.html
running soft these numbers converge. at 300 mA you can have 30C Tj, 28C Tc, 27C heatsink temp
at 3000 mA you can have 130C Tj, 90C Tc, 80C heatsink temp. thats all the resistance trying to get the heat from the chips dissipated