You may venture all types of colours from a video projector, however are you able to venture the colour black? Would not that be like capturing a shadow out of a flashlight? I imply give it some thought. Once you give a presentation, you’ll be able to have a slide with a black background. How does that work? Nicely, guess what? There’s some enjoyable physics right here, so let’s get into it.
How Do We See the Colour Black?
I wish to ask college students some questions on how they see issues. The primary is probably the most enjoyable: Have you ever ever been in complete darkness? I imply no gentle supply in any respect, not even from a crack below the door. You may need skilled that is on a cave tour, when the information turned off the lights for just a few seconds to freak you out. (Not a good suggestion; typically a light-weight doesn’t come again on.)
The subsequent query: What do you see in a darkish room? If it’s not fully darkish, your eyes will modify and you ultimately see glimmers of shapes. Nevertheless, in a completely darkish room you see nothing. A complete void. It’s sort of unnerving.
Only for enjoyable, I made a physics demo to assist individuals perceive the colour black.
Courtesy of Rhett Allain
This can be a field with a tube going into it. There’s additionally a door that you may open on the highest. The scholars look into the tube and attempt to decide the colour of the within of the field. Everybody has the identical reply—it is black on the within. I then open the highest door in order that gentle can get in, they usually see that the partitions are white and there’s an image of me in there:
Courtesy of Rhett Allain
The purpose is that if there isn’t any gentle going into your eye, your mind interprets that as the colour black.
All of the Different Colours
Do not forget that gentle is an electromagnetic (EM) wave. EM radiation can have any wavelength, from radio waves tons of of meters lengthy to gamma rays spanning only a few picometers (trillionths of a meter). And there’s a tiny sliver of this vary, from 400 to 700 nanometers, that we will see. We name this seen gentle—or simply “gentle” (although technically it’s all gentle).
Our human brains interpret totally different wavelengths of the seen spectrum as totally different colours. You may see these colours by passing white gentle by way of a diffraction grating in order that totally different wavelengths bend totally different quantities. This is what that appears like:
Courtesy of Rhett Allain
There you have got a pleasant spectrum of colours, with pink being longer wavelengths and violet being shorter. This reveals that white gentle is a mix of all the colours of the rainbow. However what about hues like brown, magenta, or cyan that aren’t in a rainbow? Nicely, these aren’t a single wavelength.
So how will we see them? It’s truly fairly wonderful. Our eyes are delicate to solely three particular wavelengths: pink, inexperienced, and blue. However by mixing these three in various intensities, you’ll be able to create the notion of any colour.
Do not imagine me? Nicely, should you’re taking a look at this submit on a pc or cellphone with a colour display, that is precisely how all the colours are created. There are a bunch of tremendous tiny lights which might be pink, inexperienced, or blue (RGB). Every of those tiny lights can fluctuate in depth to supply no matter colour you need. In case you put a small drop of water in your cellphone display, it can act as a magnifying glass and you’ll truly see the RGB lights inside.
Courtesy of Rhett Allain
However what in regards to the colours from a video projector? It basically does the identical factor. Nevertheless, as a substitute of a bunch of tiny RGB lights, it initiatives RGB colours to totally different places on the display.
Projecting the Colour Black
Now we’re prepared for the enjoyable stuff. How does a video projector shoot out black gentle? Black gentle could be the absence of any gentle, as we noticed earlier than. How do you venture nothing? First, let’s take into account a display like a TV. If in case you have three tiny lights (pink, inexperienced, blue), you may make a tiny black dot by simply turning off the lights for all three colours in that spot. Increase, it’s black!
So, is it potential that you just simply flip off the projector to make black? That may’t be proper, can it? If that was the case, you could not inform the distinction between a projected black colour and the display with out the projector even on. Sure, that’s precisely the way it works.
Test it out: Within the following picture, I am projecting a slide that’s half black and half white. The slide takes up a lot of the display.
Courtesy of Rhett Allain
You don’t see any black, do you? That’s as a result of there’s nothing there, and the ambient gentle within the room simply reveals the silver display. This is the reason we watch films in darkened theaters.
So when Darth Vader makes his look within the unique Star Wars, striding by way of Princess Leia’s spaceship? That’s proper, it’s only a Vader-shaped gap within the projected picture. The lit-up areas round him trigger our eyes to see the distinction as a deep black. There are lights reflecting off his thermoplastic armor too, including to the sense of one thing being there.
It kinda provides new that means to becoming a member of the darkish facet, proper?
