In general, you'll need more lumens for an outdoor area than an indoor one. This is because natural light is less intense than artificial light, and also because there are more potential obstacles that can block sunlight from reaching your patio. As a rule of thumb, you should aim for at least 500 lumens per square foot of patio space. So, if your patio is 10 feet by 10 feet, you'll need a light fixture that emits at least 5,000 lumens.