how lumens output a luxeon at given mA?

i have a QV0J and i drive it at 470mA, and a SV1J at 800mA

it's normal that the Qv0J is brighter than the SV1J?

there is some method to estimate the lumens output?

Lumileds data sheets (DS23: LuxI star; DS46: LuxIII star) will give you relative output at a given current.

For a Lux I, the graph doesn't go past 400mA, but I'd guess that it's around 1.3x relative output at 470mA.

For a Lux III, it's close to 1.1x relative output at 800mA.

I usually assume that any given emitter is at the bottom of its flux bin, so I'd guess ~39lm for the QVOJ and ~66lm for the SV1J.

As for why the QVOJ seems brighter... no idea. If the QVOJ is at the top of its flux bin, then it might be ~52lm, which might be difficult to tell from 66lm without a lightmeter.

i think 2 possibilities:

1) the color of the QV0J is a little on blue so appears to my eyes brighter than the warm-white of the SV1J

2) when i have solder the SV1J the emitter have take too much heat

it is easy change the aluminium star with a copper star without blow the emitter?

Are Luxeons more efficient (lumens/watt) when underdriven?

yes

leds: less mA more efficiency

incand: more volts more efficiency

So would it make sense to underdrive a Luxeon V or Luxeon III if you wanted maybe 40 Lumens, rather than overdriving a Luxeon I?