Photometry Light Measurement

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Unique human visual perception presents challenges in light measurement

Since the days of wax candles and oil lamps, man has attempted to quantify the light output from such devices in attempts to standardize production and ensure that one oil lamp was as bright as the next. As it turns out, this would prove to be a complicated problem. The visible light portion of the electromagnetic spectrum, sometimes called the optical spectrum, encompasses wavelengths approximately 400 to 700 nm containing most of the colors discernable to the human eye. However, the human eye is not equally sensitive to all wavelengths of light, being most sensitive to green at 555 nm under normal lighting conditions then to other wavelengths. Complicating attempts to measure human light perception is the individual variation in our ability to distinguish, describe, and reproduce color. A summary of average human visual perception of light would be required if any method for measuring it or reproducing its color was to be developed. Enter the CIE.