I am currently comparing the performance of a downlight (DL) in a mall space to the original lighting design. The IES file I’m using has the same lumen output as the original one — this is confirmed, as it’s the only specification they allowed me to inquire about. The beam angle is 60°, and based on the manufacturer's information, I believe any variation should be within ±5°, so it shouldn't significantly affect the result.

However, I noticed a significant discrepancy between the calculation results.

One key difference is the calculation report itself. The original calculation used an "Outdoor" utilisation profile and the calculation plane was set at -3.850 m. Based on this, I assumed that the original design was done using a .3ds model.

In contrast, I had to recreate the space from scratch in DIALux, which may have introduced some differences.

My Questions:

1. Can using a .3ds model vs. building the space directly in DIALux lead to significant differences in the lighting calculation results?
   Or is the large difference more likely to be due to something in the IES file or setup?

2. For future projects, when I need to compare different lighting products, what conditions and factors should I be careful to align (e.g., modeling method, surface reflectance, utilization profile, calculation plane, etc.) to ensure a fair comparison?

I really appreciate any insights or suggestions you can provide — thank you in advance for your help.