Measuring Daylight Using the Sigmoid Function to accurately measure total hours of daylight. May also be referred to as a Logistic or Activation function. A hyperbolic tangent function is an alternative: tanh(x) = 2sigmoid(2x) - 1. Definitions of Twilight, NWS Dave KinneyJuly 28, 2020 Facebook0 Twitter LinkedIn0 Reddit Tumblr 0 Likes