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Home Theater
Optoma HD91 Projector Optoma HD91
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Street Price: n/a
3D: Full HD 3D
Weight: 15.4 lbs
Aspect Ratio:16:9
Lens:1.9x manual
Lens Shift:H + V
Lamp Life:20,000 Hrs
20,000 (eco)
Warranty:3 year
Connectors:  Composite, Component, VGA In, HDMI 1.4a (x2), USB, RS232, 12-Volt Trigger (x2),
Video Formats:  480i, 480p, 720p, 1080i, 1080p/60, 1080p/24

Review: Optoma HD91
LED 1080p Home Theater Projector

Bill Livolsi, March 26, 2014

Key Features

LED light engine. Whereas lamp-based projectors produce white light and then split that light into primary colors through the use of either prisms or a spinning color wheel, the HD91 uses three colored sets of light emitting diodes (LEDs) to produce red, green, and blue light separately. This light is flashed onto a single DLP chip sequentially, approximating the action of a color wheel with RGB segments.

The primary advantages of an LED light engine are longevity, uniformity, and cost. LEDs are solid-state, unlike traditional lamps, and so they last much longer. Whereas a traditional arc lamp might last up to 5,000 hours, the HD91's LEDs are estimated to run for 20,000 hours.

Finally, with regard to cost: arc lamp replacements for home theater projectors can cost several hundred dollars each. With an LED projector, you never have to replace a lamp, so ongoing maintenance costs are lower if you put a lot of hours on your projector.

LED Brightness. The HD91 does not have an "eco-mode", but instead it has an LED Brightness control that allows LED light output to be adjusted between 100% and 50% at 5% intervals. This level of control is unmatched in any other home theater projector currently available.

So what's the benefit? Say you want to use the HD91 with a 100" 1.3 gain screen. Cinema mode at full power produces 517 lumens, which works out to 22.7 foot Lamberts -- slightly too high. Simply reduce LED Brightness to 70%, thereby dropping light output to 361 lumens and screen brightness to 15.9 foot Lamberts exactly. This kind of fine-grained control helps to pair the projector to your room and your screen more precisely than a typical eco-mode on a conventional lamp.

UltraDetail. Optoma's PureEngine system includes several features designed to improve the viewing experience, the first of which is UltraDetail. This enhances the appearance of fine detail by selectively sharpening certain parts of the image, similar to the smart sharpening systems on other home theater projectors. UltraDetail has two settings: "On" creates subtle enhancement, while "HD+" is a more exaggerated effect. We left UltraDetail set to "On" most of the time, only switching to "HD+" for selected content on a case-by-case basis. The system can be disabled if you don't like the effect.

PureMotion. This is the HD91's Frame interpolation system. By inserting interstitial frames in the video stream, it adds smoothness to motion and reduces judder in film. PureMotion has three settings. We used "Low" for most film content, though the digital video effect was sometimes visible, so some folks will prefer to leave the system off. "High" is best reserved for video and live-action content, where it completely eliminates judder.

DynamicBlack. Instead of a variable iris, the HD91 has DynamicBlack which changes the brightness of the LEDs in response to the content on screen, reducing light output in dark scenes and boosting it in bright ones. There are three available settings that differ in where they set the LED power floor. DB 1 varies power between 100% and 13%, DB 2 varies between 100% and 5%, and DB 3 varies between 100% and 0%. If you're not a fan of the system, you can also manually set LED power between 50% and 100%.

Color management. The HD91's color controls are second to none. In addition to the standard RGB gain and bias adjustments, the projector includes a full color management system that is designed for ease of use. If you have a color meter and some spare time, you will find it easy to bring the HD91 into line with the Rec. 709 color gamut and 6500K color temperature standards.

Anamorphic support. Anamorphic stretch mode allows you to use the HD91 with an external anamorphic lens for native display of 2.4:1 Cinemascope films. What's more, the projector has an internal setting for both mobile and fixed anamorphic lenses, making it easier to properly scale the image when you want to watch non-cinemascope content.

Dual 12V triggers. The projector also includes two configurable 12V triggers which can be used to trigger any number of external accessory devices. Examples include a motorized lens sled for an anamorphic lens, a motorized drop-down projector screen, or a masking system on a fixed-frame screen.

Full HD 3D. The HD91 is one of the first LED projectors to include full HD 3D compatibility. The projector is compatible with both DLP Link glasses and Optoma radio-frequency glasses, though the latter require an external emitter. Neither system showed significant ghosting or jitter, though as mentioned earlier light output can be a concern.  

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Comments (11) Post a Comment
crabarts231 Posted Mar 27, 2014 3:07 AM PST
If I want to turn the Dynamic Black on what Dynamic Black you guys suggest? DB1, 2, or3?? Of course I will calibrate with DB on.
Robert Posted Mar 27, 2014 10:19 AM PST
Bill, thanks for the detailed review.

One major benefit of LED projection is that brightness remains relatively unchanged over the long haul. So, once you set up and calibrate the projector, that's it.

With lamp based projectors, how much dimmer is the bulb after 100 hours, 500 hours or 1000 hours? Brightness of a new lamp tends to drop significantly and then stabilize over time. So, how long will it take for a lamp based projector to be less bright than the LED projector? Also, as the lamp fades, colors and black detail will change, requiring recalibration.

It would be interesting to compare measurements after long term testing - after 100, 500 and 1000 hours.
Edgar_in_Indy Posted Mar 28, 2014 7:57 AM PST
It would be a great selling point for LED-based projectors if they maintained their maximum brightness over the full life of the light source, but I have heard some reports from other LED projectors that they actually do lose brightness over time. So it will be interesting to see the long-term reports come in.
Bill Livolsi Posted Mar 31, 2014 2:44 PM PST
Hi everyone. Thanks for reading.

crabarts231 - it really depends on the content you're watching and the room you're watching it in. The higher levels of DynamicBlack will dim brightness more than the lower levels, so unless your room is dark and non-reflective enough to eliminate ambient light, the downsides may outweigh the benefits.

Robert - obviously this depends on the projector in question. I have yet to see a trustworthy source for long-term lamp dimming that is generalizable across all projectors, but it is clear that many projector lamps lose a chunk of brightness in their first 100 hours and then gradually fade from that point. With our specific comparison (Epson 5030UB versus Optoma HD91), I don't think the cross-over point exists.

The problem with long-term testing (and the reason why we haven't done something like this already) is that you need to maintain a normal pattern of use for your data to be meaningful. In other words, we can't just burn the lamp for 24 hours a day, 7 days a week, and expect to get results that are applicable to typical home use. Instead, we'd have to turn the projector on for smaller periods of time (say, 2 to 4 hours at a stretch), then turn it off and allow it to cool down before starting it up again. This takes a lot more time than just running the projector all day. If we used a "six hours on, six hours off" schedule on a projector with a lamp life of 4,000 hours, it would take just under a year to exhaust the lamp's life span.

Still, it is a topic that we are interested in, and we will likely write more about the differences between mercury lamps and alternative light sources in the future.

Edgar_in_Indy - To our knowledge, the projectors that suffer the largest light loss are hybrids -- those that use a combination of LED and laser sources. Pure LED projectors have less brightness but also lose less light output over their lives. Some estimates (unconfirmed) put total brightness loss of LEDs at 30% over the entire specified lifespan, and that loss is heavily weighted towards the end.
Frank Posted Apr 4, 2014 12:25 PM PST
What a great ittle projector! Of course, for LESS MONEY than what Optoma is peddling their HD91 for, you could get a PROFESSIONAL LED+laser light engine projector from Panasonic (Model PT-RZ470) that outputs 3500 ANSI lumen instead of just 1000. Just sayin'....
Stunko Posted Apr 4, 2014 2:03 PM PST
Funny that for a 1000 lumen PJ Optoma actually gives in their spec sheet a maximum projection size of 300-inches. Do the law of optics and physics support this size screen for any 1000 ANSI lumen projector, I wonder?
Frank Posted Apr 4, 2014 2:10 PM PST
"... projectors that suffer the largest light loss are hybrids -- those that use a combination of LED and laser sources. Pure LED projectors have less brightness but also lose less light output over their lives."

Trying to figure out how this goes. Okay, so a pure LED projector used R+G+B LEDs, whereas a hybrid projector uses a RED LED, a BLUE LED, and for the GREEN color, it uses a blue laser with a yellow phosphor wheel. If these LED+laser combination "hybrid" projectors lose more of their brightness than the pure LED chip projectors do, as seems to be suggested here, than the lightness loss must be related to the laser part in the hybrid, specifically the tiny blue laser gun that is used to generate the greens via the spinning phosphor wheel. I was not aware that laser sources dim over time at all, although I know that LEDs do.
Bill Livolsi Posted Apr 4, 2014 2:43 PM PST
Stunko - a projector emitting exactly 1000 lumens, projecting onto a 300" diagonal screen at 1.0 gain, would measure 3.8 foot-Lamberts. However, using a screen of equal size with a gain of 4.5 would give you 17 fL. So yes, it is possible.

Frank - I may have overstated things a little.

Some hybrid models we've tested experienced significant loss of light output over the first few hundred hours of runtime, specifically in the green channel. I'm not an engineer, but I suspect it was related to the phosphor. Then again, we tested this phenomenon years ago when the first Casio hybrid projectors were released. We did not see that same dramatic degradation in the Panasonic hybrid model we reviewed.

So far, we have not seen evidence of similar rapid degradation in projectors that are solely LED-based, but we have also only reviewed a small handful of pure LED projectors. This is something we'll be testing further as the market matures.

It's possible that the loss of green we observed in the early Casio hybrids was a model-specific problem that will not reappear in other hybrid models, but I was commenting based on my own experiences. I realize now that I phrased my comment too broadly, and for that I apologize.
Art Posted Apr 21, 2014 11:49 AM PST
Hi Bill, You done with that HD91 yet, I'm still trying to get one out of Optoma to review…

Great review, btw, I tend to agree, and do believe from my conversations with them and others, that their green problem has to a large degree tied to the design of their first (and second?) gen systems.

To Stunko, let's just say some manufacturers tend to be more optimistic than others. Interestingly 25 foot diagonal has been the favorite "maximum size" of most projectors going back to the early days. Back in 1994, the first "portable" the Proxima DP2800 projector claimed 110 lumens and claimed maximum screen size was 25' diagonal - a popular size used in a great many hotel ballrooms. Of course back then, all lights but emergency exits were normally out so that the screen was bright enough to see… Some times marketing trumps reality. -art
Doug Blackburn Posted May 27, 2014 12:33 PM PST
Calibrating with Dynamic Black ON is not going to be as easy as you might think -- I haven't thought about this in GREAT depth yet, but it seems to me that to get best results if you want to use Dynamic Black is to do calibration in 2 phases. This will be required to get decent results...

Phase 1 - Turn Dynamic Black off and calibrate everything as best you can

Phase 2 - Turn Dynamic Black ON to the setting you plan to use and as you fine tune grayscale steps and even colors, you will need to make your adjustments so that you do not change the luminance of the step you are adjusting. For example. Let's make this easy and say with DB OFF you calibrated the grayscale and you measured 10% White at 0.1 fL and you set your gamma to 2.25 (with variations in gamma that are practically inevitable, you managed to maintain your gamma between 2.2 and 2.3 for 10%-100% white). Now remember, this is with DB OFF. OK, so now you have a good grayscale and good gamma. Now, you turn DB ON and pick your setting/level (1-3). For whatever reason, when you measure some steps, especially darker steps, there are color shifts you need to get rid of. So now you measure 10% white as 0.05 fL due to the action of DB. In order NOT to screw up that gamma you set when DB was OFF (remember, your result where each grayscale step was between 2.2 and 2.3 gamma), you now need to remove some green from 10% white but when you do that, 10% white is going to get quite a lot dimmer... you don't want to let that happen. You need to make your 10% adjustments but you have to keep your luminance at 0.05 fL. So you can't just take out some green. If you were to determine that -4 on green would "fix" 10% white... your luminance level might drop to 0.04 or even 0.03... you can't let that happen. To keep that from happening, you might have to make your adjustments something like -1 for green and +3 for red and +3 for blue. That way you are removing green but also adding red and blue to keep that step from getting dimmer (these numbers are samples only, each projector is going to respond differently).

If you maintain luminance of each step after you have calibrated with DB off, you should maintain your gamma performance pretty darn well.

Similarly, when adjusting colors (red, green, blue, cyan, magenta, yellow), one of the things you SHOULD be looking at is color luminance. After you turn DB ON, your first measurement of each of the 6 colors will give you the target luminance for each color that you want to maintain as you make each of the 6 colors accurate. If your Red luminance was 3.36 fL, for example (with DB ON) but you need to tweak red to make it more accurate, you will want to do what you can to maintain that 3.36 fL of luminance which may mean making adjustments of multiple controls to keep your luminance at 3.36.

Doing this should allow you to use DB (or Auto Iris) while not introducing odd gamma behavior as image brightness goes up or down in response to the iris or changing light levels of the LED light source at different calibration settings. You may be used to having your d65 target (x=313, y=329), but luminance determines gamma -- so when adjusting any step AFTER the DB-OFF phase of calibration, you must maintain the DB ON luminance you began with... skipping that step is how we get those strange gamma results when using DB or Auto Iris.
Manuel Posted Jul 30, 2014 2:57 AM PST
Great report, though, for me one major positive of aspect of LED is the instant on and off feature, making a projector equal in speed to a TV and less hassle to start. We often use ours only 20 min/day, so this makes a difference. One question remains: why aren't there 2000 lumen LED home theater projectors yet?

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