Lumen output xhp70 at low current

Hi,
can anybody give me an educated guess on how many lumens a xhp70 6V LED will produce at 250 –500mA?
I know, its not really build for such low voltages and also pretty old today.
Thanks for your help

Refer to the datasheet, there is a relative flux curve down to 200mA.

There are also these measurements: XHP70.2 P2 4000k Output test by Texas_Ace - it's over 9000!! lumens and still going strong!

The diagram is a little inaccurate at low currents as far as I can tell.

Can anybody tell me, how much cooling I need for a xhp70 at around 5W?
I cant find anything in the datasheet for that.

Probably about 4W worth.

Oh wow, I was hoping for a little more that 20% efficiency
Thanks, though

If it 40% efficient then you need 3W of cooling.
But you want to oversize cooling a bit so i recommend 4W of cooling.