If you've never tried growing hydroponic lettuce indoors before, I strongly encourage you to try it. There are many benefits, from always having just the right amount of lettuce on hand when you need it, to the additional vitamins and nutrients compared to store-bought lettuce, to going straight from your grow area to your sandwich or salad without even having to wash the lettuce first.
If you have grown hydroponic lettuce indoors before, you're probably familiar with the lower leaves not getting enough light, and as a result dying, decaying, and sometimes even attracting some gnats as a result. I've tried spacing my lettuce pods further apart, but somehow it always seems to happen since the lettuce gets crowded and the lower areas just don't get enough light anymore.
So here's a trick I started using recently, and my lettuce has been growing better ever since. Just lying the grow deck with aluminum foil, making sure the shiny side is up. This will reflect the light back up, whether it be from sunlight through the window, grow lights from above, or both. now both the top and bottom parts of your lettuce should receive enough light to avoid some issues you may have had in the past.
Want to take it one step further? Pick up a piece of poster board, and cut it to size so you can stand it up around your growing area. Line the poster board with aluminum foil, shiny side up, then put it in place. You'll want to make sure at least six or eight inches of the poster board stands up above the base of your grow deck.
Also, if you're relying on the sun shining through the window, you'll probably only want the aluminum lined poster board to be standing up on the two or three sides of your grow deck that are opposite where the sun shines in from. If you also use grow lights, depending on the type, you may need to cut some slots in the poster board to accommodate flexible arms of your grow lights. Overall, a pretty quick, easy, and inexpensive setup with a lot of long-term benefits. I've this setup for my hydroponic lettuce and herbs for a while now, with great results.