Uniformity
Uniformity
Does the owner care about the quality of the lighting? You have fixtures 30 feet in the air and need to throw 75 feet horizontally. A good design is 1fc on average across the entire area. But, you also want to manage the ratio of brightest to dimmest. The parking lot is 13,000 sq ft. At 1fc that is 13,000 lumens. So, if the fixtures were perfect, you need 13,000 lumens of light coming from the fixtures and evenly spread on the parking lot. You need a light with a throw pattern to get the light away from the building, out into the parking lot. A narrow forward throw is needed: this has a wide horizontal spread but a narrow vertical spread. When the fixture is aimed at the middle of the lot (35 ft from the building) you want the spill toward the building and toward the farther edge of the parking lot to be acceptable. A standard flood light or high bay will not work. HPS fixtures, if the color is acceptable, are the most energy efficient inexpensive fixtures. Metal halide are better color but less energy efficient. LED are more energy efficient but pricey.
Warning: if there are paths of egress that cross the parking lot from the building, the fire code light levels must be met. That can be a challenge. In that case, you really want a lighting designer to model the situation and select the number, location, type and size of fixtures. Good luck.
