In the past, we bought lightbulbs based on how much energy, or watts, they use. Wouldn't it make more sense to buy lights based on how much light they provide?
When you're shopping for lightbulbs, you can choose your next lightbulb based on the brightness you want by comparing lumens instead of watts.
A lumen is a measure of the amount of brightness of a lightbulb -- the higher the number of lumens, the brighter the lightbulb.
Virtually all lighting fixtures emit a range of colors of light. Some, like incandescent and halogen bulbs, create a continuous spectrum over a wide range of wavelengths. Others, like fluorescent bulbs, emit a few very specific wavelengths that, when seen by our eyes, mimic white light.
Lighting manufacturers use a characteristic called correlated color temperature (CCT) as shorthand for whether a light looks “cool” or “warm”. As shown here, the higher the CCT value (as measured on the Kelvin temperature scale), the bluer the light looks.
Light that is strongly blue can be environmentally disruptive (and often harmful) to plants, wildlife, and humans. Blue-rich light also scatters readily in the atmosphere, creating lots of skyglow.
The International Dark Sky Association now recommends 2200K or lower for most outdoor lighting installations:
"The correlated color temperature of lighting used in most outdoor applications should not exceed 2200K, and where light with a larger fractional emission of short wavelengths is desired, it should be carefully controlled through stringent application of the other Lighting Principles, such as lower intensity, careful targeting, and reduced operation time." (Source: https://www.darksky.org/values-centered-lighting-resolution/)
Help reduce light pollution by selecting a dark-sky friendly fixture.
This illustration provides a visual guide to the differences between harmful, unshielded light fixtures and fully-shielded fixtures that minimize skyglow, glare and light trespass.
You can also look for the International Dark Sky Association's Fixture Seal of Approval.
IDA certifies outdoor lighting fixtures as being Dark Sky Friendly, meaning that they minimize glare while reducing light trespass and skyglow. All products approved are required to be fully shielded and to minimize the amount of blue light in the nighttime environment.
Closing window drapes and shades within a home after dark will prevent interior lighting from escaping; it is amazing how much interior light impacts the exterior environment.
The curtains in the downstairs windows in the home pictured on the right allow the indoor lighting to escape outside, while the upstairs room has its opaque shades drawn, keeping the light of that room inside.