If desired, toast the pecan halves on a baking sheet in a single layer for 10 minutes, turning once. Let them cool.
Line two baking sheets with parchment paper or a silicone baking mat.
In a 3-quart saucepan, combine the white sugar, brown sugar, and baking soda (and salt, if using).
Stir in the light cream and place the saucepan over medium to medium-high heat.
Clip a candy thermometer to the side of the pan.
Bring the mixture to a boil, stirring frequently until the sugar dissolves.
Continue to cook, stirring occasionally, until the mixture reaches the "softball" stage, which is 235°F (113°C) on the candy thermometer.
Once the temperature reaches 235°F (113°C), immediately remove the pan from the heat.
Add the butter and stir until it is completely melted and combined, which should take about a minute.
Stir in the vanilla or brandy, if you're using it, and the toasted pecans until they are well coated.
Continue to stir for about 30 seconds to cool the mixture slightly.
Working quickly, drop spoonfuls of the praline mixture onto the prepared baking sheets.
Let the pralines cool completely until they can be easily lifted from the baking sheet, which will take about 45 minutes.
Store the pralines in an airtight container for three to five days.