The higher the wattage, the more electricity your light will use. Theoretically, the higher the wattage, the higher the PAR output. Another lighting term you may see from time to time is photon efficacy. This measures how efficiently a grow light converts electrical energy into PAR. To calculate the photon efficacy of light, you can divide the known PPF by the input wattage of your grow light. The greater the photon efficacy, the more efficient a light is at converting energy into PAR, which means the less expensive it will be to grow plants.