For lighting loads, a neutral conductor is required, hence the secondary should have a star wound.
The lighting load is constantly imbalanced across all three phases.
To reduce current unbalance in the primary, we use delta winding. So, for lighting loads, a delta/star transformer is employed.
Delta-star transformers are typically utilized for lighting loads because they simplify voltage transformation & distribution, reduce third harmonic distortion, & are adaptable to various power system layouts.