Wattage Measuring

Sensors that are calibrated to the wavelength (within an acceptable tolerance) are required for accurate measuring. Obviously, commercial or scientifically calibrated ones are the most accurate and carry an expensive price tag. Some models range from $700 upwards to $2,000+. Since budget measuring was ideal, the model linked on Amazon below was stated to be calibrated for 660nm & 850nm LEDs. 

Purchased here off Amazon: 660nm & 850nm Phototherapy Light Meter

This sensor relays measurements via blue-tooth to a paired cell phone. Photos below show the readings with one of my single lights.