Post by thread:[OT] Giant redder LED displays

Hi all, Last week I went to a sign expo and was looking at a *giant* (prob >15 ft horizontal) LED display screen, as would be used for advertising. It was made up of individual red, green and blue LED's in a grid. But I noticed that in every grid "square" two diagonal LED's were red, and the others were one green and one blue -- ie: there were twice as many red LED's as green or blue. But the image colors seemed normal to me. So why more red?... Is it possible that the eye perceives red less? Perhaps over a long distance? Is brighter/more red used to make more stand-out advertisements? Did they just fill the grid spaces and reduce the brightness of the red LED's? Or...? Cheers, -Neil.

Em 28/3/2012 22:28, Neil escreveu: {Quote hidden}> Hi all, > > Last week I went to a sign expo and was looking at a *giant* (prob >15 > ft horizontal) LED display screen, as would be used for advertising. It > was made up of individual red, green and blue LED's in a grid. But I > noticed that in every grid "square" two diagonal LED's were red, and the > others were one green and one blue -- ie: there were twice as many red > LED's as green or blue. But the image colors seemed normal to me. > > So why more red?... > Is it possible that the eye perceives red less? Perhaps over a long > distance? > Is brighter/more red used to make more stand-out advertisements? > Did they just fill the grid spaces and reduce the brightness of the red > LED's? > Or...? > > Cheers, > -Neil. Some time ago, the ready-made RGB LED modules had two blue, one red and one green LEDs, IIRC, because older blue LEDs were much less efficient. Perhaps now the green and blue LEDs can be built more efficient than the red ones? By the way, Bayer filters have one blue, two green and one red cell. In analog color TV, the luminance signal is made of 0.299*Red+0.587*Green+0.114*Blue. Our eyes are really more sensitive to some colors than others, combined with the fact that LEDs of different colors have different efficiency explain the need for different arrangements. Isaac

On Wed, 28 Mar 2012 20:28:40 -0500, you wrote: >Hi all, > >Last week I went to a sign expo and was looking at a *giant* (prob >15 >ft horizontal) LED display screen, as would be used for advertising. It >was made up of individual red, green and blue LED's in a grid. But I >noticed that in every grid "square" two diagonal LED's were red, and the >others were one green and one blue -- ie: there were twice as many red >LED's as green or blue. But the image colors seemed normal to me. > >So why more red?... >Is it possible that the eye perceives red less? Perhaps over a long >distance? >Is brighter/more red used to make more stand-out advertisements? >Did they just fill the grid spaces and reduce the brightness of the red >LED's? >Or...? > >Cheers, >-Neil. A couple of probable reasons : Red LEDs are less efficient than modern green & blue ones. The Vf of red is lower than red/green - large displays are typically run from 5V supplies, so it is probably the case that for a 5V supply, two reds in series is more efficient than one, as less power is wasted in the constant-current driver. With LEDs on a square grid, using a symmetrical pattern of 4 LEDs probably also gives a more even illumination and more consistency over the viewing angle range than 3