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About Active and Passive 3D In the Classroom

By Art Feierman

About Active and Passive 3D In the Classroom

3D shows great promise.  Most of the education oriented press coming out of school districts or even individual classes that are experimenting with 3D have been generally very positive.  3D immerses the students, and that seems to help keep their attention, and in turn learn.  It’s been a while since I read any studies, but I’ll assume here, that my opening statement is still true.

There are two options for 3D in the classroom.  Active 3D, which is the same as 3D used in home theaters, and Passive, which in the US, is what you get in a movie theater, with those much lighter “passive” glasses.  Active means each eye glass has a shutter, so that for that fraction of a second, the left eye’s glasses lens is open for the left eye’s information, then it closes and the right eye’s information is transmitted to the right eye who’s lens opens.  With passive glasses, both sides of the glasses get the same information but different polarization determines what data is visible to each eye.

Generally 3LCD projectors for the classroom do not offer 3D.  There’s one exception.   Almost all education DLP projectors are 3D capable, just needing 3D active glasses.    The one thing to note, is not all of those 3D projectors support all 3D modes.  Some still have HDMI 1.3 which does not support Blu-ray 3D.  That may be an issue for some courseware, when movies, or other Blu-ray content would be shown.

Two 3LCD projectors can be “stacked” together, aligned, and with polarizing filters in front of each, do passive 3D.  Sound complicated?  Well, normally it is, but one manufacturer sells a solution ready to go.  That would be the Epson W16SK one of our Best In Classroom award winners last year.  That’s two projectors, a stacking mount, filters, etc.  Pretty plug and play.  It’s the only easy solution I know of using passive glasses.

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Active vs. Passive

Active vs. Passive:  That’s where the first big decision needs to be made.

Active glasses have one real disadvantage, which is the cost of the glasses, and the cost of replacing them when lost or stolen.  Unfortunately, missing glasses is a very likely, and very expensive problem in many schools.  Manufacturer 3D active glasses are typically $69 to $99, but the lowest priced 3rd party ones (the ones I’m thinking of are pretty flimsy), are just under $20 street price.  Still equipping a 35 student classroom, including a few extra pair, means 40 pair or about $700-$800 with the least expensive (those aren’t rechargeable, use button batteries), but typically the cost might be double that.

With passive glasses, first of all you are paying for two projectors not one.  That means a much higher starting price for the projector(s), but then in the case of our one passive solution, list price on the glasses are $6/pair and 3rd party ones half of that or less.

So, you might be paying $700 for one nice DLP projector that’s 3D capable (and can handle Blu-ray 3D), plus $700-$1600 for enough glasses to get you started, (assuming no major thefts).  Or if you go passive, you are likely paying almost $1500 for that Epson, but those 40 pair of glasses is only $200 or less, perhaps less than $100 with 3rd party glasses.

Note that the passive solution has a huge advantage in brightness, which is normally a 3D issue, as few 3D projectors can get more than 35% of the brightness in 3D relative to 2D.  With a stacked pair, you have two projectors, so starting with double the brightness, so you end up with much brighter (typically 2x as bright or more) with passive 3D.

The real savings though for passive is if disappearing glasses is a problem.  If a school has to replace 1/3 of its glasses each year, in three of four years, the dual projector passive solution starts looking like a huge bargain.   Much to be considered when choosing, not the least being what other features are desired in a projector – networking, wireless, and so on.  There’s lots of active 3D projectors suitable for the classroom, but only one passive.

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