LM7812 or ??

[spiwrx]

I'm looking at retrofitting a small LED panel to old incandescent fixture. The source is 12vac landscape light transformer that I cannot change. Actual voltage is closer to 11vac.

The panel I have works directly off 12vdc (10watt). I put a full wave rectifier on there but the voltage drop is too much, the panel barely glows. Using my DC bench supply 12vdc directly to the panels lights as designed. I can add a capacitor but considering a voltage regulator which I don't have experience with for space savings.

My question is, do I need to clean up the ripple on the simple full wave rectified AC, or can I feed it will simple rectified voltage directly.
I don't have enough room to add both capacitor and regulator. Looks like the LM7812 will suit my needs (12v 1.5a) 

[wasedadoc]

The full wave rectifier only turns the negative half cycles of the sine wave into positive ones.  Will still have significant periods of time every 8.4 ms where the voltage is very low.  That is why the reservoir capacitor is needed.  Applying 11 Volts RMS to rectifier plus capacitor is likely to produce an output around 15 Volts DC. If that is too high for the display you need the regulator.  A linear one such as a 7812 converts the excess voltage into heat. Depending on the current taken the 7812 may require a heatsink.  10 Watts from 12 Volts is almost 1 Amp so close to 3 Watts dissipated by the 7812.  Definitely need heatsinking.

[Zero999]

The 7812 can only ever reduce the voltage, not increase it, because it is a linear regulator, which burns off the additional voltage as heat, as mentioned above.

Try adding a smoothing capacitor, but my advice is to buy an LED light designed for 12VAC.

[spiwrx]

This make sense. I saw the input range was like 9-15v and thought there was hoping it would do minor compensation.

[Zero999]

Does the enclosure prevent the user from touching it? If so, then how about using a mains lamp and a small transformer to boost the voltage back up to 120V and use an ordinary mains light? A 9V transformer run in reverse will give 120V out, under load.

Note the reason why I suggested a 9V transformer, is because the secondary has extra turns to compensate for the drop under load and your voltage is 11V, not 12V. Ideally get one designed for both 50Hz, as well as 60Hz, then the extra voltage will be even less of a problem, as it's fine to run a 50Hz transformer at a slightly higher voltage on 60Hz. The obvious downside is it's not so safe, but you've still got the benefit of isolation.

[tooki]

This make sense. I saw the input range was like 9-15v and thought there was hoping it would do minor compensation.

The input range of what? Certainly not of a 7812.