The HD23 is a brighter than average home projector, although not by much. That's despite the published spec of 2500 lumens.
If you like to judge a projector based on how well the product meets the manufacturer's claims for brightness, then we have here an Optoma that doesn't come close.
But what matters is the projector's actual abilities.
I'll try to forget that this projector comes up shorter, compared to claims, than any other low cost projector, (even the Optoma HD33 we reviewed earlier this year) which was also well below claim.
Setting that aside, what we have here is a reasonably bright projector.
We are using Cinema as our "brightest" mode, and interestingly, after Mike tweaks (quick-cal) the settings for a better picture, Cinema mode gets brighter, not dimmer (dimmer is typical)!
Those numbers above, lumens and color temperatures, are all "right out of the box", without any adjustments to settings like contrast or brightness, which can affect overall brightness.
Now don't let this freak you out. As I just said, our "Brightest" mode turns out to be Cinema! Our best mode is based on the default User, and is dramatically less bright than Cinema, but still a good deal brighter than average. (On most projectors modes with names like Cinema or Theater tend to be the "best" mode, or at least one of the better lower brightness modes.)