La Palma’s “Sky Law” requires public lighting to be directed downwards to avoid direct light scatter and skyglow. Most streetlights therefore have full cut-off housings. But some lights could be better, much better. One bright example are floodlights, especially the ones used in Los Llanos’ municipal stadium.
Either these floodlights are excluded from the norm, or Los Llanos, the largest town on the island, ignores the law. In either case, the floodlights of the municipal sports stadium are not ‘light pollution-friendly’ at all:
When active, the stadium lights create a significant amount of stray light. Especially when the air is humid or dusty, the skyglow caused by the floodlights, dominate light pollution over Los Llanos. I’m quite sure that their extra skyglow is measureable from the Roque de los Muchachos as well.
Of course, these lights serve a purpose. Noone would ask to switch them off alltogether. Plus they are only switched on until about midnight. But that’s exactly the time when most touristic stargazing tours take place. And with just a simple adjustment direct stray light could be easily eliminated: Keep the lights downwards! Why should they illuminate the surrounding mountains and the night sky anyway?
There are examples on La Palma of well shielded floodlights, too. This makes me wonder why these are not standard on La Palma. The stadium of Los Llanos certainly is one of the brightest single light polluters. Its white light is visible from several elevated sites in the vicinity: