Hi Micha,

Thanks for your question here!

One unfortunate convention in optics is to use the term Intensity for two different things. Intensity is commonly used in ray tracing applications and in the optical design community to define the flux represented by a single ray, measured in Watts or Lumens. On the other hand, Intensity is also used in the illumination and radiometry fields, but the definition used there is flux per solid angle, measured in Watts/Steradian or Lumens/Steradian (Candela). So,while the quantity specified in Lumens describes the Luminous flux, the one specified in Candela is the Luminous intensity. The conversion between them is Candela = Lumen/Steradian.

You may find a more detailed description in the Help under:
The Setup Tab > System Group (the Setup Tab) > System Explorer > Units

As a further reference, you can check out this forum post that discusses How radiant intensity is defined?

If you have further questions, please let us know!

Best,

Csilla