Sheet metal has been used for the last 30+ years by lighting manufacturers to build HID and fluorescent light fixtures. Over the years these companies have become very competent trading and importing sheet metal from overseas very inexpensively by stacking it in thin layers. As these manufacturers adopted LED technology, they kept sheet metal as a significant portion of the bill of materials in their LED designs due to their economy of scale to keep costs down.
Now as LED lighting is becoming a mature technology, time has proven sheet metal is a bad choice for most parts of an LED fixture for these two reasons:
Heat sinks should have a large amount of surface area exposed to free airflow. Sheet metal ends up with a large flat surface facing upward, with air only flowing around the edges. Some manufacturers punch holes in between the LED rows to improve airflow but air is still only going around the edges. The only way sheet metal could be better is if fixtures were all mounted perpendicular to the way they are, which doesn’t make sense. Because of this thermal inefficiency vendors must reduce LED current, increase the operating temperature of the LED, or use a very thick and heavy sheet metal. None of them are good ultimately for the value, ease of installation, and life of the product.
Although it doesn’t seem the rigidity of a light fixture is that important if it survives shipping (it’s just hanging out in the ceiling, after all!) that flexibility means the relatively delicate LED PCBA is also subjected to the same strain, stress and vibrations. When vibration is present, resonance can occur which amplifies the damage. LED chips are very inflexible and can crack internally when subjected to those vibrations. The damage may not show up for several months, but it gets worse over time. Even if the company producing the fixture honors their warranty, you will be out the labor and hassle.
They are the most dependable, deliver higher performance and enable a longer LED life thanks to their superior heat dissipation. LED High Bays with aluminum heatsinks and wireways, like the Essentials Series 4.0, also benefit from higher rigidity and increased durability while keeping a lightweight design for an easier installation.