Hi OregonMEAD and welcome to this forum. If by "light refractor" you are referring to a refractometer this device can be used to measure the amount of sugar (not alcohol) in a liquid (water) - Let's call that liquid "juice". The moment that juice is mixed with any alcohol light refracts (bends) at a different angle as it passes through the liquid. In other words, while there are indeed calculators that can adjust for the percentage of alcohol in your liquid, simply using a refractometer moments after pitching the yeast without applying a set of quite complex formulae will give you a false reading.
The best use of a refractometer for the wine maker is to check the sugar content of fruit - which is to say so that you know how much (if any) sugar you will need to add to the juice (must) to raise the specific gravity (density) to the level you want/need to make a wine to the percentage ABV (alcohol by volume) you want.
The best tool for a wine maker to use to measure the approximate ABV is an hydrometer. Hydrometers measure the density of liquids where water is given a nominal density of 1.000 and water with dissolved sugars will be greater (you would look for something like 1.090 for juice for a wine and about 1.050 for juice for a cider and about the same or slightly less for wort for a beer.
Remember a refractometer measures the amount of sugar in a juice; an hydrometer measures the density of a liquid. And as the yeast ferment the sugars in your must (the juice) the density drops closer and closer to 1.000 and then drops (hopefully) a little below 1.000 because alcohol is less dense than water and when the hydrometer reads below 1.000 you know that there is no more sugar in solution so all you have is a mixture of water and alcohol with the flavors of the fruit or honey or flowers that the water and the alcohol have extracted. Hope that that helps.