Is Power Factor only relevant at rated load in Light Equipment?
Given that power factor requirements come from government regulators, you want to look at your country's rules. Here is example for US Energy Star:

https://www.energystar.gov/ia/partners/product_specs/program_reqs/Integral_LED_Lamps_Program_Requirements.pdf

It specifically says:


  Minimum efficacy, light
  output, CCT, CRI, and power factor of
  dimmable lamps will be confirmed with
  the lamp operated at full power. 


Unfortunately, I don't know if there are other power factor requiring standards -- so I guess check your jurisdiction?