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A question for the physicists

Alecto
Grafter
Posts: 2,886
Registered: 30-07-2007

A question for the physicists

Amid all the moaning (justified, I'm sure), I thought I'd ask the PhDs among the audience a question that has been puzzling me for all of three minutes:

We all know that it's better to wear white clothes in this hot weather, as white radiates heat better than black does.
But does this still work in the dark?
Will I be cooler at night in white pyjamas than in black ones, or will I need to leave the light on to get the full benefit?

Answers please before bedtime. :lol:
37 REPLIES
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

A question for the physicists

Well I'm by no means a Physicist but I do consider myself to be a logical person.

So to me logic dictates that once the sun has gone down you no longer need to reflict the heat from that source with your white clobber.

Any heat now is coming from your own body and in order for that to escape and keep ypu cool then black clothing is the attire to wear after sundown.

So white during the sunlight hours and Black Pyjamas would seem to be the order of the day.

However I accept no responsibility if by following this advice you barbeque yourself tonight. Tongue

Edited to correct some bad spelling Sad
Denzil
Grafter
Posts: 1,733
Registered: 31-07-2007

A question for the physicists

John is right, white during the day to reflect (not radiate) heat. Black is good at radiating heat but is also good at absorbing it. During the day the sun is warmer than you are so black clothes would absorb more heat than they radiate, and you get hotter. During the night your surroundings are cooler than you are so black clothes will radiate more than they absorb.

However, the amount of heat a body radiates also depends on its temperature. Human body temperature is too low to radiate very much, so the cooling effect of black pyjamas would be more than offset by the insulation they add. So if you want to lose heat at night don't wear anything Cool

Denzil
N/A

A question for the physicists

Hmm some very logical thinking right there...

I can only comment on the last line in Denzils post. Not being familiar with what PJ's are :?: I can comment on which would keep you cooler.

However as an alternative bear flesh with no quilt and a air conditioning unit blowing upon your bodies at night sure as anything keeps you chilled Smiley ( I should know I actually sleep at night lol ).
Alecto
Grafter
Posts: 2,886
Registered: 30-07-2007

A question for the physicists

Thank you for those few kind thoughts guys.

Further research on Google has indicated that black and white are both the same, and the colour won't matter till I reach 700 degrees C, so I'm off to buy a thermometer.

Meanwhile, I'm on the look out for some black and white striped pyjamas to cover both options. Which I won't wear because of their insulating properties.

My cats are very dark, so I wonder if they'd benefit from being wihtewashed during the day. I'd try it, but I don't like the sight of blood. Especially mine. :lol:
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

A question for the physicists

Quote

However as an alternative bear flesh with no quilt and a air conditioning unit blowing upon your bodies at night sure as anything keeps you chilled Smiley ).


Not sure about "Bear" flesh as it would be very furry and have a high degree of insulation. (Polar Bears manage quite well in freezing conditions).
However "Bare" flesh would be a different matter Wink
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

A question for the physicists

Don't yer genuine bedouins often wear black outer robes in the desert? Coming from an engineering/physics background I find it a little hard to come to terms with but I think I saw an explanation somewhere about the overall desert dwellers uniform that was to do more with moisture retention and insulation than thermal absorption/radiation :?
Alecto
Grafter
Posts: 2,886
Registered: 30-07-2007

A question for the physicists

In the film "Lawrence of Arabia", the really hard Arab guy (Omar Sharif I think) wore black while Peter O'Toole and all the other softies wore white.
I'd always assumed it was just to show how hard he was that he could put up with a temperature of 350 F under his kilt without blinking. :lol:
N/A

A question for the physicists

Quote
Quote

However as an alternative bear flesh with no quilt and a air conditioning unit blowing upon your bodies at night sure as anything keeps you chilled Smiley ).


Not sure about "Bear" flesh as it would be very furry and have a high degree of insulation. (Polar Bears manage quite well in freezing conditions).
However "Bare" flesh would be a different matter Wink


Its not my fault I kant speel. Wink
Alecto
Grafter
Posts: 2,886
Registered: 30-07-2007

A question for the physicists

Quote

Edited to correct some bad spelling Sad


Isn't there a saying about pots, kettles and glass houses? :lol:

And would a glass house be a good place to be at night?

ps. decided not to whitewash the cats. Shaving will be better.

Edited to complain about Tom's avatar.
I wish to complain about Tom's avatar.

And why hasn't John's avatar got any older in the two years I've been here?
Has he a portrait in the attic which ages while he stays young and fair?
Community Veteran
Posts: 6,983
Thanks: 8
Registered: 10-04-2007

A question for the physicists

Whitewash the cats by all means during the day but wash it off them at night and then brush them with coal dust. Vacuum this off in the morning and re apply the whitewash.
That should keep the cats cool and you busy enough not to rake up quotes from my posts made when I've had a few pints.

I don't like Tom's Avatar either. It makes him appear to be the sort of person you wouldn't want to meet in the dark.
Community Veteran
Posts: 5,878
Registered: 04-04-2007

A question for the physicists

I'm not sure I'd like to meet many people (or cats) on here in the dark! but at least its a tad cooler at night.
bluewhale
Rising Star
Posts: 884
Thanks: 15
Registered: 30-07-2007

A question for the physicists

what you need is something that reflects infra red as thats where most of the heat radiation is

and there will still be lots of it flying around your room as all the walls etc will be radiating after days like todays

i'm sure you could knock up a tin foil set of jamies...

it'd also keep you from being controlled by ufo's too Wink
Alecto
Grafter
Posts: 2,886
Registered: 30-07-2007

A question for the physicists

Quote

That should keep ........you busy enough not to rake up quotes from my posts made when I've had a few pints.


3.55pmHuh
:lol:
csogilvie
Grafter
Posts: 5,852
Registered: 04-04-2007

A question for the physicists

Maybe he had a liquid lunch :p