Very nice. I am always amazed at the clarity of you images. I find it hard enough to get any clear nights with light pollution I can't imagine needing 2 or 3 times as many without . Orion is in the perfect location for me right now, but we only have had one clear night in the last month and that was Christmas eve.
You need many times more clear nights imaging the same target WITH light pollution. You can get away with imaging for much less time WITHOUT light pollution.
Why? Because LP is additive to the object signal. If I'm imaging from my back yard, red zone light pollution, for every single object photon I get from a nebula, I get anywhere from 10 to 100 photons from light pollution (depends on transparency). To get 10 object photons, I have to collect 1000 light pollution photons. For 20 object photons, I've collected 2000 light pollution photons. Light pollution is something we ultimately subtract from our images...we correct a bit of it with flats, then we offset the rest. That leaves behind whatever object signal that was collected. If I offset by 2000, my object signal would still be 20. That is VERY low.
So, if my goal is to expose to about 1500-2000 e- at ISO 800, with a gain of say 0.6e-/ADU, then my image level in 16-bit integer would be something like 2000-3333 ADU. After correcting with flats and offsetting for the light pollution level, I end up with an object signal of 15-33. I could expose for longer, but because LP is compounding in the signal so much faster than the object, even if I doubled my exposure again, 4000 photons or 6666 ADU, my object signal is still only 66 ADU. Problem is, at ISO 800, 4000 e- is already getting close to the saturation point of an APS-C sensor, and is likely over half the saturation point of an FF sensor. That's too much exposure, your stars are guaranteed to be heavily clipped. Light pollution thus limits your object exposure depth by making your images "skyfog limited" very quickly.
Now, contrast this with a dark site. For every object photon gathered, I might gather 0.5 or 0.3 photons for skyfog (from light pollution, or at a truly dark site with 21.5mg/sq" or darker, from airglow). Then for every 2 or 3 object photons I gather, I get one skyfog photon. I can expose for much longer, or maybe just expose at a higher ISO for a similar amount of time (not generally recommended unless your imaging something REALLY dim, like the dust in my Orion Sword image.) For 100 object photons, I'd have 33-50 skyfog photons. Maybe even less (if airglow limited, you might expect about 0.1 skyfog photons for each object photon, meaning you can expose your object signal ten times stronger than skyfog.) Therefor, at a dark site, you are freed to expose for much longer, potentially as long as you want, before you become "skyfog limited"...which may be 10 to 1000 times longer or more than when imaging under light polluted skies.
If your goal is to expose to 2000e-, in a backyard with a ratio of 100:1 skyfog vs. a dark site with a ratio of 1:5 skyfog, you would have to expose 80 times longer in your backyard to gather the same number of object photons as you would at a dark site. Your gathering 20 photons per sub in the backyard, but 1600 photons per sub at the dark site. So, 1600/20, or 80x. If your goal is to expose 5 hours worth of total object integration at ~1600 photons per pixel per sub, your subs are 4 minutes (240 seconds) long, then your gathering 6-7 object photons per pixel per second at a dark site. You'll gather a total of 120,600 photons per pixel over five hours. Conversely, to get the same number of object photons from your back yard, you would be gathering 0.083 photons per pixel per second. To gather the same 120,600 photons...you would need to image for a whopping 403 hours under light polluted skies!!! Assuming you take the same 240 second subs, your still gathering 2000e-, however most of that signal is skyfog. So you would need over 6050 subs to get the same signal from your backyard as at a dark site.
Given that, on average, there are only 7 hours of total dark each night (a little more during winter, a little less during summer), it would take you 58 days to gather enough subs from a light polluted site. Assuming you started imaging an object as soon as it started rising high enough over horizon haze in the east, and continued until it was finally setting into the horizon haze in the west, you MIGHT have enough time in a single season to get enough subs to produce the same kind of signal from a light polluted yard as at a dark site. ;P (And, note, in reality, most places have a handful of clear nights a month to image, between cloudcover and the moon, so in a three-four month period of time you MIGHT get 15-20 clear nights tops...to get 6000+ subs on a single target, you would actually need YEARS to get all 57 full nights worth of imaging done.)
If your really interested in astrophotography, I highly recommend finding a close dark site. You might be surprised to find that, pointing either east or west, you have one closer than you think. There are a lot of light pollution maps on the web, but most are based on the bortle scale, which is a tool for visually gauging how dark your skies are, which involves how well you can see city light bubbles on the horizons. A "true or exceptionally dark" site on the bortle scale requires that LP bubbles NOT be visible on the horizons. That isn't necessarily required for imaging, you can often find skies with an SQM reading (sky quality) of >21 within 30-60 minutes from the middle of a downtown city area. Just image in the part of the sky that is dark, and in a few hours you might be able to gather enough "dark site" data that would be comparable to imaging for months from a back yard. You can use this site, which measures direct light levels from overhead, to find potential sites that might be dark enough to image from (anything blue or darker is good enough):http://www.lightpollutionmap.info/#zoom=4&lat=4838950.03614&lon=-9735847.10785&layers=0BTFFFTT
The other option is to use a monochrome camera and narrow band (NB) filtration. Mono NB imaging blocks out 99% or more of the light, passing only very narrow bands of emission. You can image under LP, even when the moon is half or larger. The kicker here is you need a mono camera with a filter wheel and nice, very narrow band filters. A decent mono CCD is going to cost a couple grand, a filter wheel another grand, and the filters themselves could be anywhere from $400 to $1200 a piece. Expensive...but, if you don't have the ability to drive to a dark site all the time, it is the best alternative. Atik has some decent cameras and a nice filter wheel for pretty good prices, and Baader has some narrow band filters (little wider bands, but still narrow enough to be useful) for good prices. You might be able to get away with a mono CCD camera setup for about $3500 or so.