Most people buy Wi-Fi by the number on the box. That number tells you less than you think. Here is what actually matters. ◆ First, Wi-Fi is light you cannot see Wi-Fi is an electromagnetic wave, the same family as the light from a bulb, only at a much lower frequency. The two behave in a similar way. The closer you are, and the fewer things in between, the stronger it is. The light-bulb test: Picture a bare bulb where your access point is mounted. Wherever that bulb would lig