What is light pollution?
Light pollution refers to the excessive, misdirected, or obstructive use of artificial outdoor lighting. It’s essentially “wasted light” that shines where it’s not needed, causing a range of environmental, astronomical, energy, and, in some cases, health problems.
The most recognisable form is the bright, diffuse glow over urban areas, caused by light scattering off dust and gas molecules in the atmosphere. This is what obscures the stars, making the night sky appear washed out.
It severely limits astronomers’ (both professional and amateur) ability to observe faint celestial objects, as skyglow drowns out the light from stars and galaxies.
How do we measure the light pollution?
There is a system, a numeric scale if you will, called the Bortle Scale. The Bortle Scale is a nine-level numeric scale that measures the brightness of the night sky and the degree of light pollution at a given location. Created by amateur astronomer John E. Bortle, it helps skywatchers evaluate the darkness of their area for observing celestial objects, with lower numbers indicating darker skies and more visible stars. Class 1 is the darkest, while Class 9 is the brightest, typical of an inner-city sky. You can check the class of your area by the number of online services available. I won’t be judging their popularity; I will list the ones I use in my daily routines.
Minimising light pollution requires a shift in how we design and use outdoor lighting, focusing on the principle of “only light what you need, when you need it.” But, unfortunately, almost none of us – amateurs – have the influence on how the town is lit during the night.
Light pollution is one of the biggest challenges in astrophotography, but there are several effective strategies you can use, both in the field (while shooting) and during processing (after shooting).
- Broadband Filters: Block a wider range of wavelengths and are good for general skyglow reduction.
- Narrowband Filters: Block almost all light except the specific wavelengths emitted by certain nebulae (like Hydrogen-alpha or Oxygen-III). These are extremely effective for imaging nebulae, as the nebula’s light shines through while the background skyglow is mostly blocked.
A less convenient but highly effective way is to travel to Dark Skies. Use light pollution maps (such as the Bortle Scale) to find locations with the lowest skyglow (Bortle Class 1-4). This is the single most effective action.
Shoot When the Target is High. The skyglow is thickest near the horizon. Shoot your target when it is highest in the sky (near the zenith) to look through the least amount of Earth’s atmosphere and the least amount of pollution. Again, the AstroPlanner will help you to plan your sessions. It will also allow you to apply the artificial horizon, which will help you plan the shot when objects are visible above this horizon (above a line of trees or roofs).
An IT network engineer by profession. A passionate diver. Active diving instructor and EFR (Emergency First Response & Secondary Care) instructor. Technical diver TDI Advanced Trimix Open Circuit and X-CCR Normoxic Trimix. Closed-circuit diving enthusiast. Yet also an astrophotographer. After all these years, I'm still a beginner, learning the stuff to do things better.
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