Simplified estimation of the eye's response to flashing light-emitting diodes

A useful laboratory technique has been devised using commonly available optical hardware and software to accurately measure the eye's response to flashing light-emitting diode (LED) sources. A simplified version of the modified Allard technique is implemented using a silicon detector, a digital multimeter, and Labview software to collect and analyze the data. Using calibrated radiometric measurements, the method presented allows quantifying, in photopic units, the human eye's response to these sources. The procedure first requires exact conversion of irradiance measurements from radiometric to photopic units and this is done; however, during the study, it was determined that for LEDs with narrow spectra, this conversion can be simplified using an approximation. This involves taking the spectral form of the LED to be a delta function situated at its peak wavelength, which makes the conversion from watts to lumens a simple multiplication by the luminous efficiency, η(λ) value at that peak wavelength. For LEDs with a full width at half maximum of 20 nm or less, this approximation is found to be accurate to ±5% throughout the visible range