Repeated field testing on many types and optical surfaces under many conditions and hundreds of satisfied customers has proven the effectiveness of this product over and over. It also has these other attractive features: It is energy efficient. Variable settings on the controller allow maximum conservation of battery power. It has an adjustable heat range to prevent tube currents or seeing degradation. It is lightweight. It is high quality It is capable of keeping every optical surface you are using during an observing or astrophotography session free of moisture all night long. It is guaranteed to work.