[chbot] LED displays coloured filters

[Helmut Walle]

On 13/01/17 23:06, Volker Kuhlmann wrote:
> On Fri 13 Jan 2017 22:20:50 NZDT +1300, Colin Isenman wrote:
>
>> You could consider a plain grey polarizing film instead of colour
>> filters. The polarization should significantly reduce reflections and
>> hence improve the contrast of the display. To be really slick, an
>> antireflective coating on top would be nice. But maybe not necessary
>> unless you want sunlight readable.
>
> In a bright sunlit room I find the white/grey background of the display
> front and the LED-segments when not lit to be close to indistinguishable
> from lit segments. Removing the light refelcted from unlit segments
> would go a very long way.
>
> I'm not sure the polarizing would help, because neither the LED light
> nor the ambient diffuse light is polarized, but it'd be worth a try.
>
[...]

I can't but agree with Volker that a polarising filter is very unlikely 
to improve the situation, mainly because it will remove 50% of the 
desired LED light, too, while making little difference on diffuse 
reflected light. BTW, it doesn't matter that the ambient light is not 
polarised, as long as the reflected light is - but the polarisation of 
the reflected light if any will be across so many planes due to the 
geometry of diffuse ambient light rays being reflected off the 3D 
structure of the LED module that it will be pretty much near impossible 
to reduce the reflection by using a polarising filter. I would expect 
that the loss of 50% of the desired LED light would more than cancel out 
any minimal gains made by reducing reflected light...

A matching colour filter OTOH will transmit almost all of the desired 
LED light, while blocking everything else.

Anyone interested in judging where a polarising filter makes a 
difference should use a polariser as they are commonly used in 
photography and try it in different situations. They generally don't 
make a difference for reflections from metallic surfaces, as the light 
reflected by metals is not polarised (unless the incident light already 
was). They do make an amazing difference for portraits, though - saves 
you a lot of skin powder...

Kind regards,

Helmut.