Winter Sunshine

[Monika]

I would like to know if winter sunshine streaming through the windows fades fabrics.

I say that it does and my husband says it doesn't.

Who is right?

[Llamatron]

Surely sunshine is sunshine whether it's winter or summer.
I'd have thought the only difference would be that's it less intense during the winter.

[Monika]

Hi Llamatron ...... I have read that winter sun can be more intense than summer sun when it is being reflected off white snow.

Also, I'm wondering if the effect of fading is also caused by the type of rays emitted rather than heat.

The other thing which makes me think that it is likely to cause fading is that it is coming through glass and is therefore quite hot even on the coldest of days.

[heathfield]

Fading is caused by ultra-violet radiation in sunlight. The atmosphere tends to filter out this UV radiation. Much more is filtered out in winter, since the low sun means the slanting sunlight has had to pass through much more atmosphere before it reaches us.
In summer, a UV Solar Index of 7 or 8 would mean rubbing on the suncream. But in winter the Solar Index is more likely to be 1 or 2, where protection is un-necessary.
You're right about reflection from snow - but this tends to be more of a problem in high mountainous areas where the air is so much clearer, and less of the UV is blocked.

[heathfield]

They, (whoever 'they' are), say that glass blocks UV. So how come when I'm driving in summer my hands get a tan from the sun shining through my car windscreen? And why did shops used to have those transparent orange blinds to stop the fading effect of UV on goods on display in the window?

[mibn2cweus]

Ordinary soda lime glass blocks from 10 (UVA) up to 90 (UVB) percent of ultraviolet light. Although ultra-violet light is largely responsible for fading due to the higher energies of shorter wavelengths of light, even visible light from the Sun can, over time, fade some pigments and dyes.