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Rainbow Effect

If you like the way this looks,
you’ll love the HP49G!

by Joe Horn

Here you can see the “rainbow effect” at its worst, partially obliterating the face of the young, handsome, and brilliant Jean-Yves Avenard. Not only are there dark blotches all over the screen, but there is a very visible rainbow at the top of the display. As you rotate the display (with respect to the plane of ambient polarized light or of the user’s polarized sunglasses), the rainbow and blotches move about but never go away. Both are “interference patterns” caused by the interaction of the clear display shield and the LCD’s polarizing sheet.

Since stress in clear plastics can be observed by placing them between two polarizing sheets, the rainbow at the top of the screen might indicate either a stress point caused by the calculator on the display shield, or an artifact of the manufacturing process of the shield.

I apologize to Jean-Yves Avenard, whose photo is in the ROM because he was on the software team, and is not responsible for the design of the display.

This problem is not a production flaw, but a design flaw. ALL HP49G’s exhibit the same behavior. It is most visible when the sun is at an angle, or in far northern and far southern climes, or when there is any ambient reflected light, and especially when wearing polarized sunglasses.  All these photos were taken in ordinary sunlight with a polarizing filter oriented in the same plane as sunglasses.

As you can see, the “rainbow effect” is visible at any angle, and even when the calculator is turned off.

Gee, look how nice the Casio CFX-9850G Color Power Graphic display looks in polarized light.
Could it be that Casio takes this into consideration in their design?

It would seem that HP did it right with the LCD in the HP38G and most 48G’s and 48GX’s ...

... but look at this! Turn it sideways (to play Tetris or use a “vertical reader”) and BLAMMO it becomes opaque! Boo! Hiss!

Everybody tells me, “That can’t be helped. That’s how polarizers work. When turned perpendicular to the plane of polarization, no light gets through.”

Oh yeah? Then explain this to me:

Evidently Casio understands polarization better than most! Look at the display of the fx-991N; it looks perfect at any angle! I’ve been told that it must be using a “circular polarizer.” Uh-huh. Sure. Look: I don’t care how it’s done! All I know is that it can be done, so manufacturers should do it! And that includes Hewlett Packard!

UPDATE — September 2013

Good news! For the first time, HP is now using a circular polarizer on their "HP Prime" calculator!
It's legible at any angle, which is especially important for Prime's excellent color display.
Thanks, HP!

Disclaimer: I do not work for HP or anybody else. My opinion only.

“Truth is just truth; you can’t have opinions about truth.” -- Peter Schikele

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