Traditionally, Metal Halide lamps (one of the HID family types) were constructed round in shape because the bulb is rounded. It was not possible to have the HID lamps made rectangular like the fluorescent lamps.
When the first generation LED High Bay lights were built, it modeled after the Metal Halide lamp and kept the round shape. The shape was influenced by the single or multiple high wattage chips used at that time. Both this is high wattage chips LED High Bay lights and the Metal Halide lamps uses reflector to divert the light down.
Subsequent technologies advancement allows the use of higher multiple of lower wattage chips for better heat dissipation. At that juncture, the manufacturer had the choice to place these low power wattage chips in either a linear array or keep them in circular layout same as the first generation of high wattage chips LED High Bay. The One-to-One Retrofit market which kept the spacing between the lights remain unchanged for ease of conversion has inevitably led to the high use of round LED high bay in this segment.
However, the other market segment which is the new factory where layout of high bay lights are not influenced by any previous installation, the use of linear LED High Bay was preferred. Main reason is linear LED High Bay can be laid out to better match the footprint of the factory. The passage way, the storage rack aisle, the shop-floor being all rectangular in shape can be lighted up more effectively. The other reason is that linear LED High Bay do not create the undesirable “white spots”which are prevalent with round LED High Bay.