AeroGarden grow lights are specially designed to deliver the maximum light plants can use, with the lowest possible energy use. Like most lights, the total lumen output can drop over time. We've found that at about 6 months, light output drops to a point that it starts to impact plant growth. Plants can start to "stretch" for the light and look a bit scrawnier than previous crops. For that reason we recommend changing grow lights every 6 months for best growth.
This is especially true for fruiting plants like tomatoes and peppers, where lower light levels can cause flowers not to set fruit. The more light you have, the more fruit you get.
Even though the light may look the same to you, your plants know the difference, and you'll often immediately see improved growth when you change bulbs.