The light is not physical, so it can penetrate physical objects. Much or little of the light will be reflected by an object, and that object will appear to us as of this or that colour depending on the frequency of the light it reflects. The light was seen as a manifestation of the divine, if not the divine itself. The Sun and the light phenomena caused by the Sunlight was anthropomorphised, and e.g. the dawn was called Austr (Scandinavia) or Eos (Greece), the rainbow was called Bifröst/Iris, the power of the Sunlight was was called Baldr/Apollon and the Sun itself Sunna/Helios.
The absence of light was seen as dangerous, but the reflection of the Sunlight from the heavenly bodies was seen as more powerful even than the Sunlight itself. Yes; the light itself is good and pure, but it changes when it is reflected by an object. This naturally also explains why metals, and in particular gold, was to be seen as sacred, when they came into use; they reflected the light very well.
Before metals came into use the sea, lakes, rivers and water in general was seen as sacred, because it reflected the light so well. Not only did the Sunlight colour the sea when the Sun sat in the West, but the Moon mirrored herself very clearly in the sacred lakes; divine light had been reflected by the Moon, Mâni/Selene and Skaði/Artemis, and this reflected light lit up the sacred lake and the areas around it. Anyone who investigates this further will find such sacred lakes all over Europe, in place names and in lake names, and if not in names then any lake near a hill or mountain top where the Sun can be seen rising each morning. The sacred lake was an intricate part of our religion.
The light reflected from the sacred lake, the sacred mirror, was a purifying light; an elf child of the Sun god and the Moon goddess blessing man - just like Baldr/Apollon, the elf child of the Sky god and the Earth goddess did too.
As we know from Greek mythology the son of Helios/Sunna is called Phaëton, and he is known to have tried to drive his father's chariot, but lost control of it and set the Earth on fire. Selene is said to have the four Horae with Helios, and also the mortal man Mousaios.
What we can read from this is that the light from this "Moon mirror" can be very beneficial, enlightening and helpful, but it can also be dangerous to those exposed to it. This naturally confirms European folklore regarding the Moonlight, where it is described as being able to turn you into a lunatic (from the Latin name of the Moon, Luna).
This in turn explains how the beautiful Selene can have a darker side, called Hekate, a goddess of crossroads, fire, light and sorcery. Yes, when you look into this "Moon mirror" you might have come to a crossroad in life, and you will probably cither be blessed by this light or become a lunatic. You light your mind up with a light in a metaphysical sense much more powerful even than the Sunlight itself; it has been reflected by the Moon and has thus become stronger.
We know this light can trigger something in us, and the outcome can be good or bad, or perhaps it will have no effect on you. Some set the Earth on fire or become lunatics because they are not ready to control what this triggers; some walk away unaffected, because their minds had not been opened for this (yet?), but some walk away with sorcerous powers and are (from then on even more divine and much better than they were before. Try it yourself... if you dare.