How Light Causes Decay

Lighting is one of the major agents of decay to objects. Have you ever noticed certain fabrics in direct sunlight fade? Or red cars turn pink? These are due to UV rays aka sunlight. The same principle can be applied to museum objects. So it is important to keep the artefacts away from harmful rays, while still keeping them viewable to the public.

A painting after being in direct sunlight for 25 years
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A car thats been left in the sun for years
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Embrittlement

As well as causing an object to fade, lighting can also cause objects to become brittle. Ultraviolet (UV) rays, visible light, and even infrared radiation can initiate or accelerate chemical reactions within an item. Organic materials such as paper, textiles, wood, and leather are particularly vulnerable to this exposure. Prolonged exposure to light breaks down material, which makes objects fragile and prone to cracking. 

Parchment object stored poorly
and has become dirty and cockled.
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Darkening and Discolouration

When subjected to prolonged lighting, chemical reactions can occur, such as oxidation or degradation of pigments, dyes, and fibres, leading to changes in colour and appearance, sometimes causing objects to darken over time. While sunlight is a major culprit, artificial lighting can also contribute to this process.