P4X Measured Brightness on internal battery: 44 lumens
Basically, the P4-X comes in very close to claim on battery power, but not quite as good on AC.
I'm not going to bore you again, with the long version of how back in the mid-'90's, hi-performance "portable" projectors weighed in at 19 pounds and output barely 100 lumens.
All considered 70 lumens is very bright for a true pico projector. Based on our reviews, only the Optoma PK320 can beat this projector in terms of AC powered brightness. By comparison the two projectors are almost idential in brightness when running on their internal batteries.
Note, the P4X apparently does not recharge when it is plugged in, and in use. To recharge it, you'll have to leave it plugged in while off.
Let's look at the effect of ambient light. Below you will see two images of the main menu. The first was taken in our "testing room" shown here. An assortment of lights are on, providing a moderate amount of light on the screen.
The first image was taken with those lights on. The image size was 40 inches diagonal.
In the second image below, the image size was reduced to 24 inches diagonal. Just that much reduction in size (about 2/3 the square footage) makes a huge difference. Of course with the lights all off, even a 60 inch diagonal size looks better than either:
You can also see some optical reflections to the right of the rectangular projected image.
Whether this uneven leakage is typical of the P4X or only the one we received we can't acertain, but we assume that this would be typical, even if of only minor consequence.
I say minor consequence, based on the likelihood fact that you hadn't noticed anything on all the previous photos, until we just pointed this out.
P4-X Audible Noise
I believe I saw a spec of 20 db, somewhere relating to this P4X pico projector. We don't measure audible noise, but let's say this pico projector is pretty quiet. Certainly it's far lower than the full sized projectors I have in my room at the moment, including Viewsonic and Epson home theater projectors. The pitch of the audible noise is a bit high - a bit of a whine, so even if it does only 20db it is a bit more noticeable.
The bottom line, though, if you aren't sitting or standing within 4-5 feet of the P4-X you aren't going to notice its fan noise at all. Even closer, it shouldn't be any problem. Remember, by any measure, it's quieter than all but a few home theater projectors.