We want to design for 2 footcandles on a 100 x 500-foot parking lot. Given that the CU = 0.70 and LLF = .64, how many fixtures will we need? First, let's assume we'll use a 250 watt High Pressure Sodium lamp with 27,500 lumens.
27,500 lumens per lamp times 1 lamp per fixture times 0.70 times 0.64 which results in 8.12 fixtures rounded to 8 fixtures. The final number of fixtures used could be further adjusted by how the fixtures are actually laid out. Fixture layout is discussed in more detail elsewhere.
This Lumen Method calculation doesn't give much insight into uniformity of illumination. For that a Point-by-Point calculation needs to be done.
