Artificial lighting performs very important functions in the modern world, e.g. it is related to the safety of movement and enabling work after dark. However, its extensive use may lead to several adverse phenomena, collectively known as light pollution. From the point of view of biology, the presence of artificial light at night-time may have a significant, negative impact on flora and fauna. In the case of astronomy, artificial light emitted by outside light sources increases brightness of the night sky, hindering observation of astronomical objects.

The artificial light spectrum is one of key factors determining how much the night sky deteriorates from light pollution. Currently we are observing a progressive process of switching from discharging lamps (e.g. sodium) to LED sources in outside lighting. It may have a significant impact on astronomy because the spectra of LED lamps usually cover the entire visible radiation range. In their interdisciplinary article published in the Bulletin of the Polish Academy of Sciences, the authors analysed the impact of over 150 LED sources and sodium lamps with colour temperature correlated in the range of 1,000 K to about 10,000 K on astronomical observations. For each analysed artificial source a Starlight Contamination Degree (SCD) index, i.e. a volume to quickly assess the impact of light sources on the night sky, was determined. The SCD index was calculated taking into account the reflection of artificial light from different ground surfaces and its scattering in the atmosphere at different levels of transparency.

It was determined that LED lamps with very low correlated colour temperature (CCT) and colour rendering index (CRI) values may have a similar or even smaller impact on astronomical observations than sodium discharge lamps. The obtained results may have a practical application. On their basis it can be indicated what should be the parameters of LED lamps that replace sodium lamps, so that observational conditions do not deteriorate. It is particularly relevant in the case of astronomical observatories that have illuminated areas in their surroundings (cities, villages, industrial areas). In this case, it is not possible to have a zone without lighting surrounding the observatory. One way to protect the night sky is choosing appropriate lighting.

The publication by Tabaka P., Kołomański S., Effect of replacing discharge lamps with LED sources in outdoor lighting installations on astronomical observations, appeared in the journal Bulletin of the Polish Academy of Sciences Technical Sciences, 71(6), 2023.