The UKE 2AAA is a nice light with about 20 hours runtime and more throw than a Photon because of its focusing lens, but its total brightness is about the same as a Photon (single 5mm LED). The 2AAA's big brother is the UKE 4AA eLED, which uses a Luxeon at around 250 mA and runs for 12+ hours on four AA's. It's regulated and is highly regarded here on CPF. But it's a much bigger light, not really suitable for EDC for most people.
There is also an incandescent (xenon) version of the UKE 2AAA which is a little cheaper and a lot brighter, but runtime is only 1-2 hours. The Princeton Tec Blast is comparable to the UKE 2AAA Xenon but a little nicer in my opinion.
Photon-style lights are good for several hours, though they do get dimmer over that period. The dimming is usually not a big problem. If it's really dark, a little bit of light goes a long way.
Maybe you want to rethink those runtime and brightness requirements. The UKE 2AAA is bright enough for most emergencies in which a 3-led light is bright enough. And what kind of emergency do you expect needing 8 hours of runtime? That rules out the Arc AAA, one of the favorite lights on CPF, but which runs for more like 6 hours. If you're stuck after dark someplace, do you really expect to need light all night? Just stay put and try to get some sleep til morning.
You might consider the Princeton Tec Aurora headlamp at around 3 ounces. It uses three AAA's and three 5mm LED's, and should run for well over 10 hours even in high brightness mode. It also has lower brightness modes, and flashing modes which could be good for signalling/location.