In the directions for the Luster Leaf Rapitest Soil Test Kit 1601, they are suggesting that you use natural light during the day to compare the test results color with the chart rather than comparing the colors at night using synthetic light.
The test chamber is the smaller chamber to the left if looking at the picture of the product on our website. The reference chamber is the larger one on the right of the Luster Leaf Rapitest Soil Test Kit 1601.
When choosing a fertilizer, we always recommend getting a soil sample completed first so that you have a starting point when fertilizing your lawn. This will tell you what your lawn needs the most to make or keep it healthy. Quick release fertilizers make nitrogen available immediately to encourage a rapid recovery however, they can cause burnlike damage and too much can cause growth to quickly that can actually weaken your lawn in the long run. Slow release fertilizer provide nitrogen over a period of time and a steady rate, and are less likely to cause burn and can improve the overall health of your lawn. You can bring a soil sample to your local cooperative extension office for testing, or you can purchase a soil test kit.