I think the advantage of 'reduced current draw' is NOT in relation to power bills or using less mains power but more to do with less strain on the connectors and driver circuits in the machine. This would certainly be the case should you replace even half a dozen lamps with LEDs - the current draw on the circuitry/transistors/triacs and connectors would be a lot less (I'm too lazy to calculate an example).
The colour enhancement that LED allows is pretty evident.. ive seen them in STNG and it does look bloody great!!
The notion of less current draw is an interesting one though. The reduced current draw is certainly not at your 240V wall socket where you pay your bills from. The power supply in pinballs is still a straight AC transformer. Its output is determined by the winding ratio between secondary and primary.
In other words, once you apply 240V across the primary winding the secondary will pump out the same power no matter what.
You do draw less current by using LED, but the transformer does not produce less current.. what is not used in the circuit is then lost in the form of heat in the windings, so you in fact cause your transformer to run warmer.
We find this all the time in the neon industry... the transformers should be loaded at 80% of their 30mA output limit. Under this amount and you run your load harder causing a loss of time that the neon will run as the electrode shells run warm, the transformer runs hot also. Anything over this 80% limit and you attempt to draw too much current and run your transformer hard causing loss of life in that.
Straight AC transformers are designed to work within a load limit... LED in your machine will not save you any $$$'s - you have to change your transformer to do that. It is also feasible that if using ALL led you will burn your transformer out... but this is theorising and i cannot of course prove this.
Now... were your power supply a switch mode type, then yes.. it churns out what is required dependant on load... but your AC winding transformer will always convert X to Y no matter what you do, unless you change the winding ratios
