You should try with a short arc xenon bulb like the Osram XBO series. They are among other things used architecturally for emulating daylight inside buildings.

You should try with a short arc xenon bulb like the Osram XBO series. They are among other things used architecturally for emulating daylight inside buildings. Downside is you need a 70A 28V power supply and a semi-massive cooling system. And bulb lifetime is approx. 1 year of normal use.