Improving the keyboard background light

[Neelix]

Except that with the keyboard backlight, lighting up the area above the keymat well isn't actually the goal.   The goal is specifically to light up the areas under the key markings over as wide an area as possible. For that you need to keep the light bouncing around within the keymat material itself for as long as possible. The longer you can keep it in there, the further it should spread within the material.   To demonstrate the idea, hold up a piece of white paper near a lamp that's next to a wall and notice the effect that has on the light coverage on the wall itself.

What that picture and the effects you pointed out tell me is that you'll most likely get the best results if there is a layer of opaque white paint directly over the silicone on the top of the mat itself and the sides of the keys, leaving only the key tops transparent. Colouring the PCB under the keyboard white would also be useful or the same reason.

That done you can colour the top of the painted keymat any colour you like, (including black) and it will have no effect on how far light carries within the material.

- Neelix

 

[EvilDragon]

The difference between holding a piece of paper before a lamp and these pictures you see here and our keymat is:
The light is DIRECTLY below the area it should light up.
This doesn't work here, as you can't put the LEDs below on the contact pads.

So our LEDs need to be as far away as possible from the actual key so that it get's light. Because: The further you are away, the wider the area being lit by the LED.
Right now, with the paint, the light is being stopped after 1mm of travel.
So it NEVER has a chance to reach the area it should light up.

Without the paint, everything is transparent and the light travels all the way up to the actual key which it should light up (it's about 0.7cm which it has to travel), so the area that gets light is a LOT larger.

As said, take a flashlight and put it 1cm away from a wall.
Then move it back to 7cm and let me know if the area it lights is larger than before.

 

[Eight Bit]

Maybe it's an idea to keep the mat free of paint at the light entry points and paint the rest of the underside of the mat and the topside in between the keys with a reflective paint to sort of "capture" the light and let it bounce until it finds an exit.

 

[Neelix]

The difference between holding a piece of paper before a lamp and these pictures you see here and our keymat is:
The light is DIRECTLY below the area it should light up.
This doesn't work here, as you can't put the LEDs below on the contact pads.

So our LEDs need to be as far away as possible from the actual key so that it get's light. Because: The further you are away, the wider the area being lit by the LED.
Right now, with the paint, the light is being stopped after 1mm of travel.
So it NEVER has a chance to reach the area it should light up.

Without the paint, everything is transparent and the light travels all the way up to the actual key which it should light up (it's about 0.7cm which it has to travel), so the area that gets light is a LOT larger.

As said, take a flashlight and put it 1cm away from a wall.
Then move it back to 7cm and let me know if the area it lights is larger than before.

Except when there is something blocking the light. (in this case, the case)  If you put your hand in front of the flashlight It doesn't matter how far back from the wall you pull your flashlight, the light falling on your hand will never reach the wall. (at least not without bouncing around the rest of the room first, which makes it a lot less useful)

Think of the keymat more like a fibre optic cable.  It allows light to be transmitted vast distances, by reflecting the light off the interior walls until it gets to the other end. If there is too sharp a bend in the fibre, light will leak out at that point and the fibre becomes ineffective.  Removing the paint altogether means that you are letting all the light escape before it gets where its going.  Painting it white gives it the reflective surface layer it needs to keep the light inside allowing it to be transmitted further.

-Neelix
 

 

[EvilDragon]

The case is not in the way. And nope, the keymat is not a fibre.
A fibre is a light channel which transfers light from one point to the other. It also works without any surroundings.

A fibre is exactly what we DON'T need, as it would never light up the keys, as no LED is straight below one.

Besides, the case is not in the way for the light - where the key is, there's a hole in the light, and the grid doesn't go all the way down to the keymat.

 

[levi]

I've been thinking of the ideas behind a fibre optic lighting soluition.  One old soltution to lighting in confined spaces (before SMD high-power LEDs existed, I guess) was to take a glass rod, file nicks into it where you wanted the light to come out, then put a light source at the end.

The problem of simulating that effect in a rubber keymat is the reflection depends on a change of refractive index at the boundary - specifically afaik it needs a higher refractive index than the surrounding material.  Glass has a higher refractive index than air, for example.   I'm not aware of any way to make rubber with different refractive indices, nor of the necessary clearness to permit almost unlimited reflection.

One possibility would I suppose to embed high refractive index plastics in the keyboard matrix.  It shouldn't be necessary to move the LEDs; as a nick in the tube allows light out at that point, it also allows light in.  It needent also be the sort of sharp nick you make with a hand-file, it could be a moulded shape quite easily.  Only problem is cost, and I don't know how that would affect the keyboard feel.

 

[fusion_power]

This picture is also a good example why removing the black painted layer is the correct thing to do:
If you take a look at those cubes, you can see that light emits from the sides as well. The emitted light actually lights up the surrounding area, which can also clearly be seen here.
A black painted keymat has THESE SIDES closed as well. So no light will get there.

BTW: One of my daily life work is properly lighting scenes.
You can believe me I know how light behaves with different material. And using a diffusor foil to make the light more soft and less spotty is a common thing.

I know  that example is not 1:1 the Pyra keymat issue but it shows that different material alone can make an difference. If in your case the light already stops at 1mm, well than the mat was done wrong. Again, tweak the material to let more light through. There are other examples with full painted keymats and these do work without any issues. So it can't be a big problem to get an black keymat that guides light well through the insides, especialy when the whole underside is not painted. The light guides inside of the material, no matter if the outside is painted or not. At least with the right material. Are there no experts in the keymat company that do exactly these things? You deal again with problems here that shouldn't be any problems at all, very strange. 
I find tons of such pix in the net, I'm sure there are companies that can be contacted to ask what's possible and what's not, maybe even in germany.

http://img.curiousexpeditions.org/nimg/24/fb/c78fb234c108e0c6e41364762df6-600x600-0/black_remote_controllers_silicone_rubber_keypad_cover_with_backlight.jpg

http://nelson-miller.com/silicone-keypads/

 

[Neelix]

The case is not in the way. And nope, the keymat is not a fibre.
A fibre is a light channel which transfers light from one point to the other. It also works without any surroundings.

A fibre is exactly what we DON'T need, as it would never light up the keys, as no LED is straight below one.

Besides, the case is not in the way for the light - where the key is, there's a hole in the light, and the grid doesn't go all the way down to the keymat.

But don't you see,  the light not being directly below the keys is exactly why you do need to distribute the light *through* the keymat,  not outside of it.   It doesn't matter that you're distributing the light, rather than directing it to a single point, the principle remains the same.  In order for the medium (be it fibre optic or in this case the keymat) to transmit the light where it needs to be, that light needs to stay within the medium until it gets there, or the medium can't do its job. 

-Neelix

 

[fusion_power]

But don't you see, the light not being directly below the keys is exactly why you do need to distribute the light *through* the keymat, not outside of it. It doesn't matter that you're distributing the light, rather than directing it to a single point, the principle remains the same. In order for the medium (be it fibre optic or in this case the keymat) to transmit the light where it needs to be, that light needs to stay within the medium until it gets there, or the medium can't do its job.

Of course the light must go through the keymat, in the meaning of going through and spreading inside of the material itself. ED also means that for sure. It just needs the correct material, not to transparent and not to opaque of course. I found an article about an similar issue another company had to deal with: Overcoming a Challenge to Backlight a Rubber Keypad Overcoming a Challenge to Backlight a Rubber Keypad
"Do you have any applications that you’ve been experimenting with to include backlighting? What challenges have you come across, if any? We’d love to hear your feedback and thoughts onbacklighting rubber keypad applications."

 

[bismuthdrummer]

Think of the keymat more like a fibre optic cable.  It allows light to be transmitted vast distances, by reflecting the light off the interior walls until it gets to the other end. If there is too sharp a bend in the fibre, light will leak out at that point and the fibre becomes ineffective.  Removing the paint altogether means that you are letting all the light escape before it gets where its going.  Painting it white gives it the reflective surface layer it needs to keep the light inside allowing it to be transmitted further.


-Neelix
 

Fiber optic cables work by having very specific indices of refraction on the core and cladding to keep the light inside the cable (see: total internal reflection). The sharp bend causes light to escape only because when light hits the inside from a 90° angle (or an angle beyond a calculable tolerance), it passes through entirely.  This is the precise opposite of diffused light, which is scattered in all directions.

I think that's the point you were ultimately touching on, except that we already have diffusion. We want to increase is the luminosity behind the keys. The problem with diffusion is that light loses energy very quickly from dispersal. The solution is to remove any barriers preventing light from taking the shortest path. Attempting to trap it for a longer period just results in lower luminosity due to the increased energy loss.

EDIT: So your point about the white paint is not entirely wrong, it's just that I'm not sure it's really needed. The keymat is not transparent up to the paint but instead translucent so we don't need to invest effort in further dispersing the light.
 

 

[Grench]

Going outside the box a bit...

Long ago we had discussed the idea of only printing the symbols on otherwise white keys -and everyone hated it from an aesthetic perspective.  But...  would that cure the current issue?

There are two ways to think about backlighting.  Most common is to want 100% even lighting behind all symbols.  I expect that will be hard to attain.  The other way is as islands of reference using pools of light as a guide.  That would function OK, but would not be as pretty.  Hmm...

 

[fusion_power]

It's a simple backlit silicone keymat like gazillion exist on different devices and they all work and light up well! I disassembled an old mobile phone by myself and oh wonder, it had covered keys and was basicly only a rubber mat (with a reflective metal layer underneeth but oh well). I see 0 reason why the Pyra keymat should not work. We can expect that the company that does this mat has experience with such materials, otherwise I would strongly suggest to switch to another company. All they have to do is to provide different samples of rubber/silicone with different transparency and "frosting" levels so ED can choose which one works best. It's not like ED had to re-invent a backlit Keyboard from zero.  :rolleyes:

 

[F_Slim]

The case is not in the way. And nope, the keymat is not a fibre.
A fibre is a light channel which transfers light from one point to the other. It also works without any surroundings.

A fibre is exactly what we DON'T need, as it would never light up the keys, as no LED is straight below one.

Besides, the case is not in the way for the light - where the key is, there's a hole in the light, and the grid doesn't go all the way down to the keymat.

But don't you see,  the light not being directly below the keys is exactly why you do need to distribute the light *through* the keymat,  not outside of it.   It doesn't matter that you're distributing the light, rather than directing it to a single point, the principle remains the same.  In order for the medium (be it fibre optic or in this case the keymat) to transmit the light where it needs to be, that light needs to stay within the medium until it gets there, or the medium can't do its job. 

-Neelix

To me it looks like you both mean the same thing, but you don't talk the same language.
The way I understand it, the problem is that the keymat is entirely black. Look at a picture of one: it's a big, black rubber-mat with keys on top. So if you light up the black rubber-mat from below (with an LED sitting between the keys), there is hardly any light seen through the keys (because the light of the LED does not spread wide enough before it hits the mat directly above it). If you use some semi-transparent rubber instead of black rubber, the light can diffuse into the actual mat and therefore reach the keys.
I think this is the effect that you (Neelix) thought of when you brought up the fibre, only that a fibre does the opposite (it does not diffuse the light but directs it to one point). We don't want the light in one point, we want to spread (diffuse) it.

 

[fusion_power]

You can see the underside of the mat, it's white, not black. only the top is painted black. But yes, the solution is simply semi-transparent rubber to spread the light inside of the material far enough to reach teh labeling. The correct value of how transparent/solid the material is must be tested.

https://boards.openpandora.org/uploads/monthly_2015_10/Backside.thumb.jpg.86c876ca68fc7e140e073ef7cc611b24.jpg

I just see plain white there, no wonder it does not work well.

 

[EvilDragon]

The reason you only see plain white here is the flash of the camera I used
The material is indeed semi-transparent.

 

[Grench]

Maybe silver paint both sides except where the LEDS and letters are then black/white/Fn?  If the light can be kept moving instead of being absorbed by the black paint, it could make a difference.  

 

[fusion_power]

The reason you only see plain white here is the flash of the camera I used
The material is indeed semi-transparent.

Yupp, and it is on a white table. But it made me concern that you do not even see any indication of the backside like the buttons itself or the black paint showing through the underside in some way. So it must be pretty opaque. Well, the method may be correct (it really should work this way) but the material is just not adjusted. I still don't see a real issue here, just needs different samples to test. No need to redo the PCB with more LED's etc.

 

[Mr_Loon]

From ED in OP : 'Instead of 1 LED for 4 keys, we'll use 1 LED for 3 keys. The downside is that this will increase the costs of the Pyra a lot... by 0,40 EUR.'

This might be impractical and a little daft but would it be possible to use 1 LED per key, pretty sure our devs could find some cool uses for this (things like only illuminating the keys required for game / app control etc.)

Must admit I've got no real concept if this idea would over complicate things or would  be simple as there are already loads of LEDs on the board.

 

[elvissteinjr]

That wouldn't work as the LEDs can't be placed below the keys, only between them.

 

[Yoyobuae]

Assuming the keymat will be mostly transparent, is there anything that could be done on the top side of the keymat (where black paint was) to "pipe" light into the keys?

I mean, instead of just letting light scatter freely, maybe some shapes could be built into the keymat to direct or spread light, specially in the directions it is most needed (ie. towards the keys).

Could the keymat material work as a lens?

EDIT: Quick diagram (assuming refraction index of keymat is greater than 1):