LEDs and voltage optimisation
"Voltage optimisation" - essentially reducing mains voltage so that it is at a lower voltage than average, is almost certain to be a waste of money and have negative rate of return in your application. 


ie In most applications VO is expensive snake oil. In a very few it may be worthwhile BUT you need to know why and design the system well. In almost all cases, don't even think about it. 


In your application they are almost certainly of no value because an LED tube's inbuilt power supply is designed to operate the LEDs at a designed operating point and designed power level. To do this the supply takes the available mains voltage and draws whatever energy is needed to operate the LEDs correctly. If the mains voltage is increased the current drawn will decrease proportionately. Similarly, if the mains voltage is decreased the current drawn will increase proportionately. In each case the input power will be essentially the same.  

I say "essentially" as the efficiency of the mains AC to LED drive converter will probably vary somewhat as mains voltage varies - but this will vary with design and possibly amongst inits of the same model, and the worst case differences are liable to be small.

It is possible but unlikely that the tubes that you are buying have a significantly greater efficiency at some input voltages than others. In this unlikely event the optimum voltage may be at the low end or high end or at the average expeccted mains voltage. This would be due NOT for the reasons that voltage optimisers are claimed to work for (lower Vin = lower power draw) which can apply in SOME special cases, but due to manufacturing and design issues that the voltage optimiser maker is unaware oif and unable to design for.

If you really care you could take say 10 tubes and operate then from a variac from Vmin_allowed to Vmax_allowed in say 10% steps and see if there is any useful change in efficiency for a single tube and, if so, if this is consistent across the samples tested. It is extremelt likely that this will prove that a voltage optimiser serves no useful purpose here.



VO's and PFCs

Voltage Optimisers have some overlap with PFCs = but usually not much.

Simplistic mains AC to LED drive circuits tend to draw high current at mains voltage peaks and lower current as voltage drops in a cycle and then probably no power for much of the ranage around zero crossing.
This leads to large current peaks at voltage peaks and no current for a large part of the cycle. This can be "deconstructed" as a current waveform rich in harmonics - the end effect is effectively low power factor and violation of regulatory standards aimed at exactly this issue as electronic loads increase. To meet standards modern LED drivers incorporate waveform correction circuitry - also able to be seen as power factor correction circuitry, which converts the current drain to essentially mains frequency sinusoidal with less than an allowed amount of distortion.
A "good" voltage optimiser may well deal with peaky loads as a part of its voltage shifting task. Failure to do so would make them unsuited to some roles due to regulatory non-compliance. This is no guarantee that they actually will behave as desired. If the load already draws essentially sinusoidal current the VO serves no purpose in that area and probably little or none on any other.



Related:

VO - Wikipedia

Jeff Howell - fergetaboutit

Some real tests - Bzzzzzzt