The claim that the Quran describes the speed of light with the phrase "12000 lunar orbits/Earth day" involves interpreting a specific verse in the Quran through a modern scientific lens. This interpretation is based on the idea that the angels travel at an incredible speed, as described in Quran 32:5:

Here’s how the argument is developed: - Lunar Calendar: The people in the Quranic context measured time based on the lunar calendar, with each year consisting of 12 lunar months. The verse mentions "one thousand years of what you count," referring to the lunar calendar system. - Interpretation of the Verse: The verse suggests that angels travel a distance in one day equivalent to 1000 years as counted by the lunar calendar. The argument made here is that this distance is analogous to the distance traveled by the moon in 12000 lunar orbits, or about 12000 lunar months, in one Earth day. - Speed of Light Comparison: This concept is then compared to the speed of light, stating that the distance angels travel in one day, as described in the Quran, is equal to the speed of light when measured in terms of lunar orbits. In modern science, the speed of light in a vacuum is approximately 299,792 kilometers per second, and this interpretation suggests that the Quranic verse, when measured in terms of lunar orbits, corresponds to the same distance that light travels in one day. -Orbital Mechanics: The idea is that over the course of one day (one Earth day), the moon completes approximately 1/30th of its orbit around Earth (since there are about 29.5 days in a lunar cycle). Thus, the total distance the moon travels in 12000 lunar orbits in one Earth day, when calculated using orbital mechanics, corresponds closely to the distance light travels in one day.

The interpretation of Quran 32:5 as describing the speed of light through the "12000 lunar orbits/Earth day" comparison is a modern interpretation, which links ancient descriptions with current scientific understanding. However, it remains speculative and varies in acceptance depending on one's approach to the Quran and its verses—whether literal, metaphorical, or symbolic. Whilst these verses might not necessarily reference the scientific findings mentioned here, they clearly showcase how the guidance mentioned in the Quran are very much scientifically possible.