QP Lightpad™ And Future Observations

QP Optoelectronic’s Lightpad appears to me to be an interesting “transitional product” in the evolution the pico projector “use model”.    In this post I am going to comment on what I think they got right and what will need to be improved to make pico projectors more useful.

The Lightpad combines a rear projection screen, keyboard with touchpad, WVGA (848×480) DLP pico projector, and battery that folds up into a thin form factor.   In effect it turns a smart-phone with HDMI output into a netbook (except that is for the currently for a non-jail-broken iPhone which does allow “mirroring” of the phone’s display) .   The phone acts as the computer with all the software on it, but you now have a larger, easier to read screen and a reasonable size keyboard for typing.  The projector can also be flipped around in a front projection mode to give a larger on say a wall or screen in dark environments.

The Lightpad address one big issue I have with the typical pico projector shoot on the wall use model, namely that there is almost never a white wall, in the right place with low enough ambient lighting to be useful.  The “shoot on the wall” use model only seem to work in very contrived demos.   The Lightpad addresses this issue by having a built-in rear projection screen.

The rear projection screen, as opposed to say a sheet of white paper address a very important issue for pico projectors, namely giving sufficient contrast in typical room lighting.   As I discussed perviously about ambient light, even a dimly lit room has 1 to 2 lumens per square foot and a well-lit room has 30 to 60 lumens per square foot.  It turns out that you want at least 10 to 1 contrast for a reasonably easy to read text, so with a 10 lumen or even 30 lumen projector you can’t project a very big image with much contrast on a white screen.   A rear projection screen is designed to only accept light from a certain range of angles behind it and reject most of the random room light coming from everywhere else.  Because of this “ambient light rejection” a rear projection screen will result in higher contrast in the final image.  So the rear projection screen enables lower lumen pico projector to be very usable in brighter room light conditions.

The keyboard on the Lightpad makes typing easy and the touchpad in front seems to integrate well with the touch interface on the front of the keyboard.  Because the rear projection screen is lightweight plastic, it solves the weight and potential breakages issue of carrying around a large LCD screen.   I could definitely see this type of product being useful for the professional that doesn’t want to carry a laptop with them.  As big an advantage as any being that all the software and data on your smart-phone is available to you without needed to worry about sync’ing or buying a bunch of software.

While I like the concept and QP got many things right in terms of functionality, there are both some short, medium, and long-term improvements that will hopefully be made over time by QP Optoelectroncs and/or other companies.

Short Term (Easy) Improvements

The most obvious flaw, one in which QP says they are working on to improve, is the rear projection screen.  In particular, it has a “hotspot” where if you look at the projector straight it is very bright in the center.    The hotspot effect is show in the picture at the left (but please note a camera exaggerates the effect so it is not as bad as the picture shows but still present).

The next issue, somewhat evident in the picture at the top of this article, is the size and bulk of the cables.  Some of those in the picture are associated with power that will not be there in portable use, but still there are some long bulky cables and adapters between the smart phone and the Lightpad.   In my experience, the cables can often take up more space than the pico projector itself. I would make the cables much shorter, smaller, thinner, and they should easily store into the Lightpad.

Medium Term Improvements

With their announcement of the Lightpad, QP optoelectronics also announced that they are working on a 720p (1280×720 pixels) version.    This certainly would be welcome as many of the newer, more advanced, smart phones are supporting 720p and higher resolutions and one of the big reasons to project a bigger image is to be able to see more.   It really doesn’t make much sense to project a large image if it low in resolution.   Having higher resolution would enable more normal notebook like use for applications such as editing and viewing documents, working on presentations, internet browsing, and spreadsheets.

Long Term Improvements

While Lightpad is light and about the size of a pad of paper when closed, it still does not fit in your pocket.  So you are left to have something to carry around. The really big volume potential for pico projectors is in having something that fits in a normal pocket so it can be with you wherever you go.   Improvements in LEDs and laser light sources should significantly reduce the size of the projector and its battery, but then the issue of the rigid screen and the physical keyboard.

Today with 1 Watt, only about 7 to 10 lumens is possible with LEDs and LCOS or DLP including the light source and light modulator (currently laser beam steering is far behind needing about 3 Watts to give just 10 lumens).   Realistically with significant improvements direct diode lasers and incremental improvements in the light modulators, in a few years it should be possible to produce to about 30 lumens per Watt.    If we want an image that covers about half a square foot, about the area of a small laptop LCD, that means we could get to about 60 lumens per square foot.   If the ambient lighting is normal room lighting of 30 to 60 lumens a square foot then we would only have 2:1 or 1:1 contrast and a very washed out image.  So even with major improvements in pico projector technology we will need to look for a dark corner of the room or still want some form of light controlled screen.

To make the screen easily portable it should roll up into something about the length of a pocket pen (about 6 inches long) and less than 1-inch around (about the size of a white board marker).    Making rollable rear screens with good light control and uniform light spreading (avoiding hot spots) is not that easy as generally there needs to be things like a Fresnel lens which wants to be rigid.  3M has developed Vikuity™ rear projection plastic films  that don’t use Fresnel lenses but these are still meant for rigid installation on a glass or Plexiglas rigid surface.  Perhaps something like the Vikuity materials could be made rollable.

While rear projection screens are the obvious approach,  a perhaps better rollable screen approach would be to use a “wavelength selectable” (WS) front screen.   With a wavelength selectable screen, only specific wavelengths of light are reflected and the other absorbed.  Since normal room or sunlight is “broad spectrum” most of the ambient light is absorbed.  The WS coating could be made on thin rollable plastic.  Sony made a rigid form of WS screen called the ChromaVue™ back around 2005.   At the time Sony said that they could make a rollable version with the same technology but it never came to market.  ChromaVue screens were designed to work with fairly broad spectrum projectors using high pressure lamps with color filters.  Unfortunately, manufacturing costs and low volumes of the ChromaVue screens appears to have caused Sony to stoop making them several years ago.   The task of making a WS screen with narrow band LEDs or Lasers should be much easier so I would think that we will see the re-emergence of WS screens in the future.

Virtual Keyboards and Other Input

Inexpensive camera input should enable the elimination of the physical keyboard with the pico projector projecting the image of a keyboard.  The use of cameras for input is becoming commonplace today with devices such as the Microsoft Kinect™.  In fact, many people in the field expect that pico projectors and cameras will commonly be paired together in future application.

In the case of a rear screen projection one technique is to use infrared cameras (CMOS cameras naturally detect infrared) to sense when and where the screen is touched such as with the Microsoft Surface®.  One advantage of the rear screen infrared approach is that it is relatively easy to detect when the screen as been touched.

There are more issues with a front projecting virtual keyboard.   The first of which is that it become very desirable to project the keyboard at a shallow angle so that the project does not have to be so far away from the surface of a table.   The shallow angle also means that the keyboard will not be blocked as much by shadows cast by one’s hands.   The use of laser light in pico projectors will make short throw, shallow angle projection much easier to implement.

A bit of a technical challenge with front projection keyboards is to know when a key has been pressed versus a finger hovering over a key an there is a lot of work going on in this area.   With structured light (for Microsoft presentation on structured light click here)  and/or multiple cameras detecting finger pressing versus hovering is possible.   One can also expect some quicker input like Swype to be employed.


My expectation is that we will see the pico projector evolve from today’s shoot on the wall gimmick/toy to being a really useful product.    I think the QP Lightpad makes a good first step in the right direction.   It is much easier and with faster adoption rates to use already successful user interfaces and use models than to try and create new ones.     At the same time one needs to live within the physics of what is possible, such as how many lumens will be possible in the coming years for a pocket size device.   The technology for virtual keyboards and multi-touch displays is becoming very advanced and should not be a limiting factor.

Karl Guttag
Karl Guttag
Articles: 247


  1. Hi, Karl,
    I am glad to tell you that we have done your suggested near term improvement. Thanks for your suggestion and look forward to demo the product to you.

  2. Mr. Guttag, it ispossible to see products based on the new 720p panel after the lawsuit?, everything is so quiet on syndiant’s site. I hope the 720p panel will see the light soon.

    Any new pictures that you can share?.


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