Hello ,
Thank you for posting your question in the community and at this time this file format is not supported with lights objects in Twinmotion. You can however use IES profiles which are more commonly used worldwide from my understanding.
Here is a video tutorial I found to convert LDT files into IES files:
https://youtu.be/yP6VCyF9nFc
If you think this is something that is going to have a big impact to have this file type supported with light sources you can submit an idea on our road-map for consideration: https://portal.productboard.com/7pu88c9kpmqtzt8hwg6arujh/tabs/4-under-consideration
Hope this helps.
Kind regards,
Vincent B.