Power Saver in Lighting Load

I have no recommendations other than to be alert for scams or concepts that don't really do what they claim.

I would echo Tornado's warning and also add that you are likely to experience a drop in illumination levels.

Yep. Chuck out the tungsten lamps and replace them with something with a higher lumens-per-watt performance, with the aim of maintaining lumens and reducing watts. There's loads of lamp vendors on the internet and many other places. Is there an electrical distributor nearby, for example?

Being and Energy Auditor, I have seen lots of fluctuations in lighting feeder supply voltage. If you are in rural area, voltage fluctuations are higher than city areas. If you have any control mechanism particularly for lighting feeder without adding additional transformers is one way of saving couple of bucks. (Ex. proper functioning of online tap changer, reducing voltage by offline tap changer considering minimum rated voltage of luminaries). Adding transformer to lighting feeder will add transformer losses which will get compensated by saving few watts after reducing voltages but will definitely reduce illumination so is not a good idea. There are lots of other options for energy saving possibilities in lighting load and I will advise you to explore those first.

Most of the "power saver" units for lighting are nothing more than a re-labeled version of the Nola energy saver circuit for AC motors. The problem is, all it can affect in a lighting system is the voltage to the circuit, essentially reducing it to the lowest common level. As mentioned above, this reduces the illumination levels. If you can accept having less light, install lower wattage lamps or remove a percentage of them, same effect.

Human finger is the best brand for this job.

please study monthly tariff of an industrial load such as 3-part tariff for better understanding.