My two cents: raw sugar contains 3% impurities, which are mostly molasses, and has a large, irregular granule size. Light brown sugar has been refined to a pure white state, had its granules made smaller and more consistent, and then has molasses added back to it. The raw sugar will have a more complex and tasty flavor, but will have a larger and less consistent crystal size and probably not be as consistent in molasses content as light brown sugar.
From a baking standpoint, the two most significant differences between raw and light brown sugar are the granule size and molasses content. You haven’t mentioned the recipe you are using. If you are dissolving the sugar in a hot liquid, then granule size doesn’t matter. If you are making a cake, you might want to blitz the raw sugar in a food processor to reduce granule size so that the cake’s crumb will have a fine texture.
Re: molasses content, the raw sugar is likely to have less molasses, about 3% by weight. If we use Rose’s weights for granulated white sugar (1 cup = 200g) and light brown sugar (1 cup = 217g), it appears that light brown sugar is about 8% molasses. That means that if your recipe has baking soda in it, it may need to be reduced when subbing raw for light brown in order to avoid a soapy taste from too much baking soda.
To sum up, it depends on the recipe- in a custard you probably wouldn’t need to make changes for the substitution, but making a cake that called for baking soda might require grinding the raw sugar to reduce particle size and subbing baking powder for a little of the baking soda at a rate of 4:1. Hope that helps!