A driver controls current, a LED will always have a driver, it could be a simple resistor or capacitor or it could be a PWM unit. If the driver is a simple resistor then it really does not matter if you control voltage or current to that resistor, however with a PWM unit any change in voltage with be auto compensated for until the limit is reached, and any control of current again until you reach maximum current it would work but over that maximum it could cause the voltage to raise above the value that the PWM unit can handle.
So with a PWM device the dimmer unit needs to talk to it. The PWM may read the clipping of a leading or trailing wave form as an instruction to reduce the current. As electricians we tend not to reverse engineer lamps, we simply read manufacturers data. As said Magaman has a good site listing what will and will not work with their lamps.
Using cheap lamps the efficiency drops, many LED bulbs are as low at 60 lumen per watt, and some of the strips are even lower, but where the LED unit is designed to replace a fluorescent lamp then they tend to be far better more like 100 lumen per watt as other wise not worth replacing the fluorescent as the fluorescent with a HF ballast is coming in at 90 ~ 95 lumen per watt. Also those designed to replace DC powered lamps also tend to run at 100 lumen per watt, they likely have to use PWM control to take the variable voltage often rated 10 ~ 36 volt. However both the extra low volt DC and the fluorescent tube replacement tend not to be dim-able.
If I was to design a rooms lighting then maybe I would worry about the lumen per watt, but where the design is an existing one, swapping 10 CFL for 10 LED since the CFL was so poor in the first place unlike the larger fluorescent tube, I would not worry if only 60 lumen per watt, it will be better than what it replaced.
As to dimming since there is no ambulance I see little point, they stay the same colour so may as well simply use less or more lamps rather than dim them. The problem with dimming is it can cause a stroboscopic effect as the two devices used to control them don't match. All too often a bulb fails and one buys a replacement at the nearest store. And then the problem starts. All well and good getting 10 bulb which match the dimmer to start with, but unless you hold a stock, then 5 years down the line your trying to find bulbs that work with your make of dimmer.
