Why is black better than white for sun protection?

[physicsforlife]

OK, so people say that wearing white is better than wearing black in the sun because white reflects light whereas black absorbs light.

But at the same time it is said that black is better for sun protection (for example, darker skinned people are much less likely to get skin cancer than lighter skinned people).

Are the two phenomena even related? It's confusing to me because you would think that black would be worse for sun protection because it absorbs light.

Thanks for any help.

 

[ZapperZ]

OK, so people say that wearing white is better than wearing black in the sun because white reflects light whereas black absorbs light.

But at the same time it is said that black is better for sun protection (for example, darker skinned people are much less likely to get skin cancer than lighter skinned people).

Er... the latter has nothing to do with "black or white" skin, but rather the nature of the pigment in the skin. So it isn't about reflection or absorption due to colors only. This is now more of a biology/physiology question rather than a direct physics question.

Zz.

 

[physicsforlife]

maybe the skin example was a bad one.

here's another one: it's better to wear dark hats and clothes for uv protection rather than white ones. a scientist said this somewhere, but s/he didnt exactly explain why. it seems counterintuitive to me.

 

[johnintheuk]

the pigments in white coloured materials emit and reflect more spectrums of light back. Black pigments absorb it and convert it to conducted heat.

if you wear black clothes, they need to be very loose fitting.

 

[mgb_phys]

Thin white cotton t-shirts, especially after they have been washed a few times don't block very much UV so might not be protecting you from sunburn as much as you think.

The dyes in dark colors are better at absorbing (=blocking) UV.
Of course they also absorb more energy and so heat up more, but if they are loose and not in contact with your skin it doesn't really matter what temperature the material is at.

 

[physicsforlife]

thanks a bunch!

 

[anon123456789]

Thin white cotton t-shirts, especially after they have been washed a few times don't block very much UV so might not be protecting you from sunburn as much as you think.

The dyes in dark colors are better at absorbing (=blocking) UV.
Of course they also absorb more energy and so heat up more, but if they are loose and not in contact with your skin it doesn't really matter what temperature the material is at.

im quoting you because you are a physics guru that answered this question and hopefully you can respond. okay so i asked this same question thread starter asked and i got a different answer. the answer i got was that you can't take the properties of objects in the visible spectrum as an indication of what happens in the UV spectrum or any other spectrum for that matter. this means that you can't tell unless there has been some testing with the dyes and fabrics.

 

[mgb_phys]

you can't take the properties of objects in the visible spectrum as an indication of what happens in the UV spectrum or any other spectrum for that matter.

That's true in general, it would be possible to design a dye that was black in the visible but transmitted UV completely. But in practice you wouldn't .

White T-shirts generally don't contain any dye they are simply bleached to remove the natural color of the cotton. They are also usually the thinnest cheapest material because they aren't being processed as much as colored ones. There is very little UV absorption in the material an there are a lot of gaps between the fibres for the UV to go through.

A dye will absorb a range of wavelengths to give the color you want, generally the heavier the dye the more has to be absrorbed and since UV rays are more easily absorbed (higher energy) then in general the darker the dye the more UV is blocked as well.
For traditional clothes like a bedoiun's black robe the thick heavy wool material also helps.

For synthetic materials the dyes are more carefully designed because the polymers the fibre is made of are damaged by UV and so you usually have to ad UV blocking elements to the dyes. And since the dye is chemically incorporated into the fibre it doesn't usually wash out. The makers play on this necessity by advertising them as UV protection swimwear/beachwear. But remember it also depends on the thickness of the material and the weave - a string bikini of thin UV blocking polyester still isn't going to block as much UV reaching your skin as a thick woolen robe.

 

[anon123456789]

A dye will absorb a range of wavelengths to give the color you want, generally the heavier the dye the more has to be absrorbed and since UV rays are more easily absorbed (higher energy) then in general the darker the dye the more UV is blocked as well.

are you saying that darker dyes block more UV because they are usually a heavier dye?

For traditional clothes like a bedoiun's black robe the thick heavy wool material also helps.

i got that same answer from another member, that to dress for hot sunny weather you take cues from the bedouin. on a somewhat related note, bedouin seem to dress quite thick, as seen in this photo - http://en.wikipedia.org/wiki/File:Bedouinwomanb.jpg
wouldn't dressing like that be hot in the desert? or is it just clothing that is very loose and big and its just me thinking its thick?

 

[sanijerum]

thank you so much.i like this topic..hiki...hiki..hmmm...

---------------------------------------------

sanijerum

hdbfkdhkjsd@sycodas.cz,cvzxdkuyf@sycodas.lt,fgjhdf@sycodas.lv,fduifh@sycodas.md,gfnhdjs@sycodas.me,yfgtsduihf@sycodas.pl,hgjthgot@sycodas.sk

 

[Dadface]

are you saying that darker dyes block more UV because they are usually a heavier dye?

i got that same answer from another member, that to dress for hot sunny weather you take cues from the bedouin. on a somewhat related note, bedouin seem to dress quite thick, as seen in this photo - http://en.wikipedia.org/wiki/File:Bedouinwomanb.jpg
wouldn't dressing like that be hot in the desert? or is it just clothing that is very loose and big and its just me thinking its thick?

Dark clothing can absorb more heat but if it is loose fitting it can set up a convection current with hot air leaving the top of the clothing and refreshing cooler air flowing in from the bottom.The air flow can further enhance the cooling effect by increasing the rate of evaporation of sweat from the skin.A nice example of solar powered air conditioning.

 

[mgb_phys]

Correct, it's also very cold in the dessert at night.