I have a customer who has existing,400 watt MH low bay lights in diesel truck repair shop.they are spaced fairly normal. 20-25 ft apart & 15-18 ft high.They are not getting enough light at lower levels when working in engine compartment. I am thinking of adding some t8 low bay lights in between the existing lights. I am unsure yet as to number of lamps per fixt.Can use 4 or 6 lamp fixtures. Any others have input or experience with some thing like this? Thanks in advance for any advice.Do I go safe & just use 6 lamp?