A see-through iPhone hit the Google+ "What's Hot" list this week. One day later, a transparent-display iPad hit the list as well. (I posted the second one.)

The "What's Hot" list is Google's ongoing popularity contest for posts on Google+. The clear-screen iPhone and iPad posts inspired a lot of talk about whether such displays are feasible and, if so, desirable.

The general consensus: "Cool! I want one!"

Transparent-display iPhones and clear iPads don't exist, of course, nor have they been announced or even hinted at by Apple.

The pictures are "design fiction" -- drawings and videos created with the help of software to create the illusion of reality.

It's clear that transparent displays are bad for mobile

The good news is that transparent-display phones and tablets are possible. The bad news is that they're undesirable.

Docomo and Fujitsu built a prototype transparent display for a multi-touch mobile phone. (The touchscreen works on both sides!)

This research may have inspired designers to engage in some Fujitsu-branded fantasy design concepts that included a display that toggles back and forth between transparent and nontransparent modes -- for example, showing words in a book one moment, then the words translated into another language the next -- much like the pretty Word Lens app I told you about previously in this space.

The blog Concept Phones has been publishing pretty pictures of fantasy phones for years. They've become something of a banality on the design-fiction sites.

Real transparent-display phones will probably become available within a few years. But they'll never go mainstream.

Display quality is important to users. Phone and tablet makers work hard to maximize the quality of displays. Apple says its Retina display is the best in the industry. Some reviewers say displays in some Samsung phones are higher quality or more or less the same quality as the iPhone's display, but bigger.

On any display, picture quality requires clarity -- black blacks, white whites and vibrant colors. If the background bleeds through from the other side, picture quality will suffer, even if companies figured out how to make a see-through screen as high resolution as a conventional display.

The replacement of a high-resolution screen for even a high-resolution transparent screen would involve a dramatic reduction in image quality.

The need for long-lasting batteries is a another problem facing companies interested in developing see-through screens. Because they must last as long as possible, batteries these days are so big that they occupy most of the physical space inside smartphones and tablets -- so it would be pointless to have a transparent display. If companies want to offer see-through displays, they'd need very small batteries that fit somewhere near the top or the bottom of their devices, and such batteries probably wouldn't last very long.

Most users won't be willing to sacrifice image quality and battery life for the novelty of transparent displays.

Why transparent displays have a bright future

Transparent display technology is coming, just not to phones and tablets.

Rather than transforming computer screens by making them transparent, this technology will instead transform transparent things into computer screens.

For example, it will be applied to windows. No, not Microsoft Windows. I'm talking about the glass windows we have in our offices, cars and homes.

Samsung actually sells a transparent display device. Called the Samsung NL22B, the $2,805.99 device is an aquarium-like box with regular glass on the sides, a transparent display on the front, a lockable door on the back and a PC built into the base. It's designed for display marketing, whereby a store places its product (or whatever) into the box, then uses Samsung's MagicInfo software to display moving words and pictures on the transparent screen.

Other companies, including Crystal Display Systems, have shown similar products recently.

Even more interesting is the touch-based Smart Window that Samsung demonstrated at the International CES trade show last month. In the demo, the display is placed in front of a mini cityscape, suggesting that it could be installed as a window in your office. It basically just throws up a Windows-like desktop on the window.

It's easy to imagine incorporating this technology into a home, as the makers of the Iron Man movies did.

Transparent display technology will be used in eyewear, such as glasses, goggles and scuba masks, enabling reality to be augmented. It is one of those exciting areas of innovation where science fiction is about to become very real, very soon.

Just don't expect transparent screens in your phones or tablets. Because while that idea yields beautiful design fiction pictures and videos, it makes for a lousy mobile device.

Mike Elgan writes about technology and tech culture. You can contact Mike and learn more about him on Google+. You can also see more articles by Mike Elgan on Computerworld.com.