Efficacy is a measure of a lamp's energy efficiency.
The efficacy of a lamp is determined by the amount of light output, measured in lumens, per watt of energy used. CRI measures the effect that a lamp has on color appearance of an object. The higher the number, the more accurately the lamp renders the true color of an object, up to a maximum of 100. It should be noted that CRI is different from color temperature, such as warm or cool white. By way of demonstration, here are some examples of Compliance and Non-compliance.