I observed a fascinating demonstration of how science doesn’t come naturally to most people yesterday.
There were five adults present along with a two-year-old. The two-year-old had a toy that shone a picture in yellow light onto the surface it was pointed at.
Someone suggested the child shone the picture on their (black) trouser leg. I pointed out it would show up better on their white sock. ‘Surely,’ came the reply, ‘yellow would stand out better against black than white?’
Three out of five adults were Cambridge graduates – but still the immediate consensus without thinking about it, apart from me, was that a yellow light would show up better projected on black than on white.
After a little thought, at least one came round to my line of thinking, but the rest put up a defence. ‘What colour is a movie screen?’ I asked. ‘That’s different,’ they said. ‘That’s in the dark.’
What this little encounter made me think is that we are inudated with art in kindergarten and primary school. Art tells us that yellow will show up better on black than white. But we get very little thinking about science – so don’t really question how limited this view is. Similarly we get told the primary colours are red yellow and blue, not red, blue and green.
I’m not suggesting we stop youngsters playing with paints, but I do think we should give them more science-based toys to play with so they discover more at the same age how light acts. Arguably also we should teach colour first from a light-based view and then consider pigment, rather than the other way round.
Whether or not you agree with that, the reaction of those in the room with the two-year-old was a salutory lesson. C. P. Snow would be turning in his grave.
On or against black?
On if it’s a pigment, against if it’s a fabric…
The whole thing boils down to transmitted versus reflected light, and the primary colours are different in each case. I’ve come across this recently when formatting color pictures in Mallorn (the Tolkien Society journal wot I edit). When people send you a jpg, it’s meant to be seen in transmitted light, like a stained-glass window, and the primary colors are red, green and blue (RGB). Before I send these to the printer I have to reformat them to CMYK (cyan, magenta, yellow and … er … black) so that the color balance will look the same in reflected light, that is, when it’s printed on paper. CMYK approximates to the blue, red and yellow primary colors we learn about as toddlers when we’re messing around with paint. Having said that, I’m still not sure about Brian’s question above. I guess that a yellow light shone onto a black surface would be absorbed, so we wouldn’t see anything much.
This is one of those things that its quite hard to get your head around why it works. A bit like ‘why is your reflection in a mirror reversed only in the horizontal plane and not the vertical plane as well?’
Absolutely, Henry – black should absorb all appropriate frequencies (unless it’s shiny black, but let’s not get into that), so the projected yellow hippo should disappear on the black trousers, as indeed it did. Of those present apart from myself, a mathematician got it wrong, but then said ‘hang on a minute, this needs think about’, while the other, non-sciency types were convinced, even when I brought up the matter of cinema screens.
When I say ‘non-sciency types were convinced’, I mean convinced the yellow light would show better on a black ‘screen’ than a white one.
Why can’t we edit comments?! We deserve to be told.
Everybody knows the movie screen is silver, that’s why they call it the silver screen.
RGB for screen. CMYK for print.
I’m surprised that no-one (in your description at least) made the empirical observation, rather than standing around arguing! (To be fair, this is exactly what I would assume the two year old would be getting on with :)
Anna – as I mentioned, one of those present was a mathematician, with a couple of arty types too. Practicality doesn’t really come into it. (We did the experiment eventually, but the argument was primarily about what people’s immediate reaction was to the concept, without thinking too much about it.)
Jeff – Movie screens have been both silver and white over the years (I think you’ll find modern screens are closer to white than silver), but certainly never black!
Cameron – the mirror thing did cause confusion for a while before clear explanations came along, but they have now. The whole thing is a misunderstanding. Mirrors don’t rotate in any plane, they invert front to back. Look at yourself holding a magazine when standing in front of the mirror. If you hold the mag (Nature, of course) with the front page towards the mirror, the mirror person is holding a mag with the back page (which just happens to have an inverted version of your front page on it) towards the mirror.