Find a Projector
Award Winning
New Projectors
Projector Brands
Screen Brands
Projector Lenses
Find a Projector
Subscribe
Optoma's newest home theater projector is what many have spent years waiting for - an affordable, high-quality 1080p projector with a solid-state light source. For a retail price of $3,999, the Optoma HD91 combines the features and functionality of Optoma's top of the line home theater models with an all-LED light source anticipated to have a life span of 20,000 hours. The HD91 does not cut corners, and the projector includes all of the modern conveniences (like a long zoom lens, lens shift, frame interpolation, detail enhancement, and full HD 3D compatibility) that home theater enthusiasts have come to expect from this class of projector.
Editor's note: this article has been updated. Information relating to the cost of the projector has been corrected, and our evaluation has been edited to incorporate this information.
We set up the Optoma HD91 on a rear shelf in a light-controlled room and connected it to our Oppo BDP-103 reference Blu-ray player over HDMI before turning the power on. The image jumps to life on the screen mere moments after you press the power button. One of the advantages of LED projectors is that they require no warm-up period, and instead start up at their full brightness.
The first thing we noticed, and one of the important limitations of the HD91, is the projector's relatively low image brightness compared to competing home theater projectors. Our test sample measured 517 lumens in Cinema mode at full power, which is low by today's standards. However, if care is taken in positioning and mounting the projector, that is still enough power for a 120" diagonal 1.3 gain screen, so the HD91 is still capable of large-scale projection.
The image without calibration can look odd, especially if one is accustomed to the appearance of lamp-based projectors. Color is intense, with very high saturation and brightness, while black level is only average. However, these flaws were easy enough to remove thanks to the projector's extensive calibration controls, and the resulting image is smooth, life-like, and accurate. Shadow detail is particularly impressive once the gamma curve has been fine-tuned.
The HD91 has a number of image enhancement features, most of which are located under "PureEngine" in the Advanced image menu. UltraDetail increases detail perception (we left this set to "HD," which is the middle setting) while PureMotion is a frame interpolation system (we left this either on Low or off, depending on the type of content being used). There's also an iris-like system called DynamicBlack, though rather than a physical iris, the system uses changes in LED power to adjust image brightness.
The end result of all of our tweaking was an image that had vibrant color and excellent depth. Foreground objects seem ready to leap off of the screen thanks to the projector's high contrast in most scenes. The projector's black level is incrementally higher than some other home theater projectors that have aggressive automatic irises, but this only becomes apparent in scenes where black is a major component of the image (such as dark scenes in movies or scrolling credits) and was not apparent in mid-toned or bright scenes.
When it comes to 3D, image quality was quite good. The HD91 uses either radio-frequency or DLP Link synchronization at a refresh rate of 144 Hz, which means little crosstalk or ghosting. However, given the light output limitations of the projector, we would not push screen size over 100" diagonal for 3D viewing.
With a 1.9:1 zoom lens and H/V lens shift, it's not difficult to get the HD91 set up in a typical home theater environment. However, the relatively low light output of the projector means that you'll be better off placing the projector as close to the screen as possible to avoid further light restriction from the zoom lens.
The HD91's 1.9:1 zoom lens will allow you to display a 120" diagonal image at throw distances from 13' 1" to 25' 2". However, at maximum telephoto, the lens loses 46% of the projector's total light output, bringing our test sample's 517 lumens in Cinema mode down to only 278 lumens. That's usually not enough light for a 100" diagonal screen, only giving 12 foot Lamberts on a 1.3 gain surface. If you need to use the telephoto end of the zoom to achieve the placement you want, consider going down to an 80" diagonal screen with a mild positive gain in order to boost image brightness. This goes double for 3D projection, where brightness is further curtailed.
As far as lens shift goes, the manual H/V shift will allow you to place the image either completely above or completely below the lens centerline, for a total range of two image heights. Horizontal shift gives you about 25% of the image width in wiggle room. The lens shift range is elliptical, not square, so you cannot use the projector's full horizontal and vertical shift ranges at the same time. There is no decrease in light output when using the extreme edges of the lens shift.
The HD91 is quiet during operation, though it does have a characteristic LED hum that we have noticed on several LED-based projectors. It is not loud enough to be annoying, at least in our estimation, but it can be noticeable during quieter scenes if you have the projector positioned close to the audience.
In summation, the best place to mount the HD91 is in a ceiling mount or low table placement at the minimum throw distance for the desired image size. If you can manage a rear shelf mount while still avoiding much use of the zoom lens, this is another viable option. Use a screen surface with a mild positive gain, and eliminate as much ambient light as you can.
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.
Light output. The HD91 is rated at 1,000 ANSI lumens. After a 15-minute warm up, the projector's internal white test pattern gave a reading of 880 lumens, which was the maximum sustained output we obtained in our testing. Unlike lamp-based projectors, LED-based projectors reach their maximum brightness immediately upon startup. And whereas lamp-based models "warm up" to their full brightness over a few minutes, LED-based projectors like the HD91 actually lose brightness over the first few minutes until they stabilize.
The brightest usable image mode was the aptly named Bright mode, which measured 840 lumens. Bright mode emphasizes green, reduces contrast, and is locked to the DynamicBlack 3 power setting. It is suitable for max-brightness applications like watching sports in a room with some ambient light, though its low output means that ambient light should still be curtailed as much as possible to avoid washing out the image.
Cinema mode is the preferred operating mode for home theater use. At 517 lumens, Cinema mode offers much better color and contrast than Bright mode while still maintaining most of its light output. Photo mode, at 513 lumens, is similar to Cinema mode, though it contains small changes to gamma and color saturation that enhance the visibility of mid-tone detail. The remaining modes are Reference (408 lumens) and Film (386 lumens), both of which attempt to provide a more accurate image than Cinema mode but sacrifice light output to obtain it. Overall, we felt that the trade-off was not worth the loss in brightness, so we stuck with Cinema mode for most viewing.
The biggest brightness concern on the HD91 is the 1.9:1 zoom lens. At the telephoto end of the zoom, the lens reduces light output by 46%, bringing Cinema mode from 517 lumens to 278 lumens. Be aware of this reduction before mounting your projector.
Contrast. Out of the box, the projector's black level is a touch higher than some other home theater projectors, but some fine-tuning of the projector's gamma controls can improve black level significantly. Black level after calibration is comparable to many other home theater projectors. Contrast in any given scene, on the other hand, is particularly good. The picture showed above average pop, with great background separation and three-dimensionality.
Care should be taken when setting the projector's gamma controls, as the projector has excellent shadow detail once calibrated but doesn't look particularly impressive out of the box. Our preferred setting uses the 2.4 preset with a -3 offset. On our test unit, this gives depth to shadows without crushing detail and vastly improves the projector's contrast and shadow detail.
While DynamicBlack is primarily a brightness control, it also improves black level in dark scenes. While the choice of whether or not to use DynamicBlack is ultimately yours, we do offer this word of advice. If you plan to use DB, calibrate your projector with DB enabled. The DynamicBlack control alters the power levels of the LEDs differently, so a perfect calibration with DB turned off will undergo significant color shift if DB is then enabled later.
Color. The HD91's color controls are intuitive and comprehensive, so it is easy to calibrate the projector if you have the knowledge and equipment to do so. If you don't, you can hire a local AV professional to fine-tune your projector.
Sharpness and clarity. The HD91 has a crystal-clear HD image with plenty of detail, and that's without using the projector's UltraDetail sharpening system. With that system engaged, fine detail jumps out from both standard-def and HD content. The effect can actually be a little overwhelming if you're using a source that is already high in detail, such as The Dark Knight or Baraka on Blu-ray.
Input lag. After extensive testing, the HD91's lag performance the same in every image mode provided PureMotion is disabled. With PureMotion off, the HD91 measures 76 milliseconds of input lag, or about four and a half frames on a 60 fps signal. PureMotion increases lag to 126 milliseconds (7.5 frames).
Light output. Compared to competing home theater projectors the HD91 isn't very bright. The projector's calibrated Cinema mode measured only 517 lumens, and using the telephoto end of the zoom lens can reduce light output to as little as 278 lumens. These days, it's not uncommon to see Cinema modes in the 800-1000 lumen range. Since the HD91 has much lower brightness than these other projectors, it is important to mount the projector carefully in such a way that you minimize use of the zoom lens. If you cannot do this, you'll need to use a smaller screen to keep image brightness up. This is especially important if you plan to watch a significant amount of 3D which cuts brightness at least another 50%.
HDMI sync time. The HD91 takes longer than average to lock on to an HDMI signal, which can be frustrating at times. In addition to being somewhat annoying during film and video use, the slow sync makes it difficult to switch resolutions on source devices, most of which now require confirmation of the new resolution. We ran into trouble trying to switch resolution on a Western Digital WDTV Live, since that device's 10 second timeout expired before the HD91 located and synchronized with the new signal.
Menu display time. The HD91's menu will only stay open for a few seconds before it disappears again, and this display time cannot be changed. On the other hand, if you press enter on any individual control, it will display a single-line adjustment control that never times out. This makes it easier to calibrate the projector, but also removes the menu from view when you aren't actively working in it.
Input lag. The HD91 has a minimum input lag of 76 milliseconds. Home theater users will want to use an audio delay to eliminate video/audio synch problems, while gamers who value fast response times should not use the HD91 as their primary gaming machine. On the other hand, I managed to play Skyrim on the Playstation 3 for several hours without noticing any problems, so gamers who don't need lightning-fast response can continue using the projector without worry.
Lens shift. The HD91's lens shift has good range, but the actual shift controls can be difficult to use. The two lens shift dials are both oriented in the same direction, so it's hard to remember which is horizontal and which is vertical. What's more, the dials are situated underneath the projector, and it can be difficult to reach down and adjust them without jostling the projector around.
Cost. A retail price of $3,999 puts the HD91 in an interesting position. On the one hand, it performs similarly to several lamp-based home theater projectors in the $2000-$2500 price range. But it is priced up in the $4000 range with several high-performance projectors. This puts the consumer in an interesting position: they can pay less for equivalent performance or the same amount for better performance.
Optoma HD91 versus Epson Home Cinema 5030UB
For a competitive comparison, we set up the Optoma HD91 next to the Epson Home Cinema 5030UB, a lamp-based home theater projector that sells for $2,499. Both are 1080p projectors built for home theater from established manufacturers who've had a lot of time to iron out the kinks.
When considering strictly image quality and leaving aside brightness, it's amazing how similar these two projectors look. Both do a wonderful job putting highly detailed, high-contrast, well-saturated pictures on the screen, and both calibrate to the established standards without much fuss. If your only concern is your ability to get a high-quality HD image onto an appropriately-sized screen, either projector will suit your needs. If you have requirements about the size of that screen, or where it is located in your home, continue on.
The 5030UB produces much more light than the HD91 in both its brightest and calibrated modes. Dynamic on the 5030UB produces 2230 lumens, making it nearly three times as bright as the HD91's Bright mode at 840 lumens. The 5030UB's Cinema mode measured 805 lumens, giving it a significant brightness edge over the HD91's Cinema mode at 517 lumens. And the 5030UB also has Living Room mode, which produces 1550 lumens with color and contrast that aren't much different from Cinema mode. In other words, you can get roughly three times as much light out of the Epson 5030UB.
This means that the Epson 5030UB can serve double-duty in a living room while the HD91 cannot. It means you can shine the 5030UB onto a 140" diagonal screen without compromising color or contrast. It also means that you can watch 3D on a much larger screen when using the 5030UB. And it is easier to mount the 5030UB using the longer end of the zoom range without reducing image brightness to unacceptably low levels.
The 5030UB also has an advantage in black level, especially in dark scenes, thanks to its iris. The 5030UB has an excellent auto-iris system, and while DynamicBlack is an interesting solution, it cannot match the speed or the effectiveness of a good iris. Brightness changes on the 5030UB were faster, more dramatic, and less noticeable than on the HD91.
On the other hand, the HD91 has an advantage in single-frame contrast, especially in brighter scenes. The HD91 appeared dramatically three-dimensional next to the 5030UB in these scenes, despite the 5030UB's strong contrast performance. This is not a flaw in the 5030UB, in other words, but a strength of the HD91.
As far as color is concerned, the 5030UB is more accurate out of the box, but both projectors calibrate to Rec.709 and 6500K. And, honestly, you should not be purchasing either of these projectors if you don't plan to calibrate them.
Neither projector had a clear advantage in terms of detail, but the 5030UB did have one advantage in terms of clarity. We saw significant temporal dithering in the HD91's image, which isn't the same thing as digital noise but can have a similar appearance (and a similar effect on your enjoyment of the picture). The 5030UB is not without noise itself, but that noise can be reduced by using the projector's noise reduction system. Since temporal dithering is an artifact of the technology itself and not a signal problem, it cannot be reduced through image controls.
Features. The HD91's LED light source has an estimated life of 20,000 hours, while the 5030UB's lamp is estimated to last from 4,000 to 5,000 hours. If both light sources last for their full lifespans, the HD91's LED source is equivalent to four or five 5030UB replacement lamps, which would cost between $897 and $1196. That brings the lifetime cost of the 5030UB up to $3695 -- roughly equal to the HD91's $3999 price tag.
But by purchasing the 5030UB and the spare lamps, you get a projector with the same 20,000 hour lamp life that is three times as bright. That extra brightness gives you the flexibility to use large screens, or mount the projector near the back of the room, or watch large-screen 3D. These things are much more difficult to accomplish on the HD91.
And this is all assuming that you'll actually use the projector for 20,000 hours. Few people do - that is 10,000 2-hour movies, or one movie per day for 27 years. In other words, 20,000 hours is a very long time, and most folks will replace their projector before they get anywhere near that much viewing time. If you decide to replace the 5030UB before you reach 20,000 hours, the extra money you would have spent on lamp replacements is still in your pocket. With the HD91, that extra cost is built in to the projector. There's no opting out.
The HD91 has anamorphic stretch mode, something the 5030UB lacks. The HD91's three-year warranty is one year longer than that of the 5030UB. Both projectors have full HD 3D compatibility, frame interpolation, smart sharpening, excellent placement flexibility and lens zoom, and low fan noise.
All in all, the HD91 produces a very good cinema image that is comparable to that of the 5030UB. However, the 5030UB's light output advantage allows it to display that same great image on larger screens, or in less perfect environments, or from longer distances -- all of which would compromise the HD91's image to the point where it is no longer competitive.
The Optoma HD91 is among the first LED-based projectors to be built specifically for home theater use. When you view it in this light, it is a remarkable product. It combines the refined cinema image that enthusiasts have come to expect with all of the modern features and functions found in lamp-based models, then adds an LED light engine with an estimated life of 20,000 hours.
Of course, nothing is free. In the case of the HD91, the trade-off is light output. Compared to other home theater projectors, the HD91's 1000-lumen spec is already quite low, and the reality of its 517-lumen Cinema mode is doubly so. It limits your placement options despite the projector's excellent 1.9:1 zoom lens and can in some situations effectively confine the projector to smaller screen sizes.
With televisions getting larger and larger, the main advantage of projectors is their ability to use very large screen sizes. But the HD91's relatively low light output means that, should you mount the projector in the back of the room, it is limited to screen sizes that can be matched by a large television.
Don't be mistaken: the HD91 is a great home theater projector, and the image it produces is definitely competitive with lamp-based projector models. You just need to take care when mounting and installing the projector to ensure that you retain enough brightness to light your desired screen size. And with a little bit of work, it is still possible to put the HD91 on a 120" diagonal screen. So if you're finally ready to stop buying replacement lamps, the HD91 might just be the projector for you.
For more detailed specifications and connections, check out our Optoma HD91 projector page.
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.
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.
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.
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.
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
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.
