Protction from Sun rays
Protction from Sun rays
(OP)
Hi,
which colour umbrella will give best protection from Sun rays during very hot sunny day?
Thanks,
KMPillai
which colour umbrella will give best protection from Sun rays during very hot sunny day?
Thanks,
KMPillai





RE: Protction from Sun rays
Martin
RE: Protction from Sun rays
Thank you for your response. I agree with your reply. Let us say the material is cloth.In some regions in south Asia most of the people are using black colour umbrella during summer also. Is there any reason behind that. From the heat transer point of view, I think white colour will give best heat protection.
KMPillai
RE: Protction from Sun rays
Funny question here, because it reminds me to a quite long discussion i had during my study. Well, the conclusion was that the color you SEE is not relevant. Since you ask for the thermal properties you must consider the IR-range of the sunlight. This is in fact the reason for the heat you feel, but the visible color of e.g. a fabric does not necessarily represent the properties for infrared. You can have black surfaces which reflect more IR then a white one. It depends on the material itself and not on its color. Though you find that (for us) ´white´ clothings reflect more sunlight (also IR?) then black.
The UV-Range of the sunlight is again different, here all i know is, that most materials absorb ultraviolet light quite well and i´d guess that the visible color is also not necessarily important for the UV-related properties.
So, sorry for my long story, but i discussed that much more already. :)
(pls let me know if you have great new findings!)
MT
RE: Protction from Sun rays
Regards,
Believe it or not : Though he couldn't prove, Einstein never agreed with Heisenberg on his Uncertainty Principle.
RE: Protction from Sun rays
Furthermore i actually wrote the same as Martin, that the surface/material and not the color mainly determines the protection level.
So long,
MT
RE: Protction from Sun rays
On the use of different colours and its properties to pure radiation heat transfer it all comes down to the emmitance number. Black objects would absorb radiational heat very quickly. Black objects would also emmit heat better. Where white and silver objects would not absorb so much heat from radiation (and rather reflect it) the same lighter coloured object would be less effective for emmiting heat it already has. The reason for Asians using black is maybe more a cultural thing. I am no UN-diplomat but isn't white clothing supposed to be a colour of mourning for some Asian cultures? Could also be because white cloth tend to be more transparent than coloured because the colour die fills up the little holes in the material. Personally I'll wear white when it is a hot day.
For the more harmfull rays (UV's) metalic surfaces are used for protection. UV's might not heat something up a lot but it is damaging because of cancer and deteriation of chemicals. That is why some surfaces of spacecraft is made of gold foil. Yep, real gold, but not enough for retirement, unfortunatly.
martindup
RE: Protction from Sun rays
Perhaps they simply know more about real-world heat transfer than you think:
http://search.csmonitor.com/durable/2000/12/05/p18s1.ht...
TTFN
RE: Protction from Sun rays
I know in Saudi during the summer, I never saw any of the Saudi men who were wearing traditional clothing in anything but white. In winter when it's cooler, you see black, grey, blue, etc but they weren't worn in the summer.
The women's clothing on the other hand in public was always black.
RE: Protction from Sun rays
Feminist activitis - No offence intended. Don't shoot me !!!
RE: Protction from Sun rays
My idea is that black might have been the cheapest color to dye a cloth.
Regards,
Believe it or not : Though he couldn't prove, Einstein never agreed with Heisenberg on his Uncertainty Principle.
RE: Protction from Sun rays
I suspect that most Saudi's visible to Westerners wear white as a sign of prosperity.
The Bedouins and Tauregs are not so enamored with Western ideals of prosperity and assuming that you could actually track a traditional one down, they would still be doing the black tents and black clothing.
TTFN
RE: Protction from Sun rays