Light beams interference.

[Robear]

Hello.I have a question wich popped up:

Suppose we send two beams of red and green light(or,lets say blue and yellow light) towards a surface,and both beams are projected at the same spot?What will we see there?Some of us said we would see:yellow and green(since red+green=yellow and blue+yellow=green) while others said it is not true...The question is,do the basic ideas about colour combinations work here too or not?

[iNow]

Hello.I have a question wich popped up:

Suppose we send two beams of red and green light(or,lets say blue and yellow light) towards a surface,and both beams are projected at the same spot?What will we see there?Some of us said we would see:yellow and green(since red+green=yellow and blue+yellow=green) while others said it is not true...The question is,do the basic ideas about colour combinations work here too or not?

 

Yes, this is also exactly how projectors work (at least older ones, but I think DLP follow this same approach). You basically have three bulbs, and they project onto a screen to create all of the various colors.

[Robear]

Just in case this question appears again,let me say,that in case you didnt know there are aditive and substractive systems.If we mix colours like yellow and blue,the classic RYB colours,well get green,however this is not the case of projectors and as it is an aditive system and the basic colours are RGB one cannot obtain the green colour by projecting blue+yellow on a surface,wikipedia says no simple colour combination will give you the green result.The aditive system is oftenly used in theatrical lighting so projecting two colours on a surface will give you a third colour tho,it will follow diferent principles.One more thing,lets say you project green and red on a surface(thus havin a yellow surface) and then project blue.My classmates said it would be usual yellow+blue=green.Actually since this is not a substractive system Red+Green+Blue=white and not green as expected.