Dark Sky Compliance requirements help protect from light pollution. Outdoor lighting fixtures that are Dark Sky Compliant shield the light source to minimize glare and facilitate improved vision at night.
A few characteristics of Dark Sky Compliance include:
Lights be on only when needed (with dimmers, timers or photo-controls)
Lights are only illuminating areas that need it
Lights are no brighter than what’s necessary or safe
Most importantly for this topic, lights must use optics or shielding to prevent “uplight”
High mast lighting will always be mounted via a Horizontal Tenon (so that the fixtures' optics are facing downward), ensuring that any IDA compliance rating is maintained. Keep in mind that you may see images of extremely tall poles that look like high mast lights, however, when high mast fixtures' optics are not pointed downward, they are not mounted properly and much of the light is wasted.
In comparison, because flood lights use adjustable angles with mounting brackets, they lose any IDA compliance rating when they are no longer oriented 90 degrees to the pole. Once flood lights are angled, the effectiveness of the fixture to generate even lighting on the ground is reduced.
Therefore, only certain flood lights will be considered IDA Compliant. Although it may be common to see “IDA Complaint” listed on a LED Flood Light specification sheet, if you read the fine print you will see that as soon as the light fixture changes its mounting angle (which is why you would use a flood light in the first place), it will lose IDA Compliance. In theory, flood lights that point straight downward (mounted at a 90 degree angle) are IDA compliant, however, this mounting orientation is not normal for flood lights and a 90 degree angle actually defeats the purpose of choosing flood lights in the first place.
Bug Rating
BUG stands for Backlight (light directed behind a fixture), Uplight (light directed upward above the horizontal plane of the luminaire), and Glare (amount of light emitted from the luminaire at high angles) – fixtures that minimize all three of these improve light quality, decrease light harshness, and are often Dark Sky Compliant.
Bug Rating is a system designed by IES and International Dark Sky Association that works together with the Dark Sky Compliance light zones, which are accepted levels of light in specific outdoor areas. When a fixture has a U0 BUG rating, it means the fixture emits zero light up into the sky – the lower the number, the better and more likely, IDA Compliant.
