|View single post by Huw Griffiths|
|Posted: Fri Feb 20th, 2015 12:59 am||
|Tramcar Trev wrote:
Then there is the black car/ white car debate and black cars get hotter in the sun yes of course they do. We also busted that myth, the black car heats up a hell of a lot more quickly but gets to a point where it re radiates the heat faster than the white car which actually gets hotter than the black car but because its white the general public believe thats they are cooler on a summers day...
It's occasionally been suggested that another issue might be how well different coloured surface finishes reflect light of different frequencies.
The suggestion was something along the lines of white surface finishes reflecting enough light at visible frequencies (red ... violet) - to a similar enough extent - to appear white under sunlight.
By the time the light frequency moved down to the infra red (effectively "heat") end of the spectrum, any pigments, bases etc in any surface finishes might well behave very differently from how they might have in the visible spectrum.
I don't doubt that these differences apply just as much to bare metal - with differences depending on how the surface has been prepared (polished, grit blasted etc).
I also don't doubt that there are many people better qualified than me to comment on stuff like this.
Also of interest to me was the initial topic of this thread - voltage step up converters.
I suspect that the key issue with using these is how much current you actually need to draw out of them. This might seem like a strange statement - but I'm not sure that it is.
A couple of years back - at an engineering trade show - I was given a "white" LED torch with a step up converter (aka "Joule thief") built in (very useful it is, too).
I'm not sure how efficient it was - but it probably doesn't need to be particularly efficient.
The whole point of this device is that it allows me to drive a reasonably usable torch from 1 "AA" cell that would otherwise have been discarded. I might only get (say) an hour out of each cell - with a pretty low current driving the LED - but it's enough so I can see my way home, if I've got a bit of a walk after I get off a coach.
It's also use I would not have got out a cell that no longer had enough "juice" to do anything else - so I'm not exactly complaining if the thing isn't quite as efficient as it might be.
Would I use a similar circuit to drive anything that needs a significant current? Probably not - if nothing else, it probably wouldn't work. However, for a really low current application - where it allows me to get away with using batteries which would otherwise be completely useless - I can't think why I wouldn't wish to use something like this.
For me, the key is how much current it needs to supply - and whether I'm actually too bothered if the thing isn't quite as efficient as I might sometimes wish.
Anyway, sorry about the interruption - back to the thread.
Last edited on Fri Feb 20th, 2015 01:08 am by Huw Griffiths