The sensor response in voltage output is linear with the of irradiance from each source as both the response curve and the distribution of radiation from both sources are constant. Because the design of the system allows for the determination of the measured incident radiation due to the artificial source, the contribution to the sensor reading from natural light can be determined and thus the total sensor response can be decomposed into artificial and natural contributions. With the sensor response decomposed thusly, the contribution of each source to the human eye response can be evaluated similarly. For a commercial system it would be preferable to select a sensor more closely tailored to the visible light spectrum or incorporate light filtering films to the design of the sensor itself to address the variable spectral distributions of reflected light; however, for use in the laboratory test bed where the largest portions of measured light are direct light components this decoupling procedure is deemed sufficient. In order to determine the visible light contributions from the two sources, transformation factors are calculated. These factors are evaluated by comparing the numerical integral of the original emittance and spectral power distribution curves with the product of these curves and the relevant response curve. By comparing the results from the photopic curve and sensor response curve computations, the measured sensor response can be converted to the equivalent visible spectrum value. Using the response parameters for the selected sensor, the luminance value is computed using Equation 3-1. [3-1] D/A Module The hardware design for the digital-to-analog (D/A) converter enables direct and robust software implementation. The eight pins on the Atmega64 port C are connected in parallel with the eight input signal pins on the D/A allowing the port C pins positions, when initialized as digital output pins, to function as the bits of the control signal. The desired light level fraction is converted to a fraction of the maximum value represented by the eight bits, 255, and this value is written to port C.
The sensor response in voltage output is linear with the of irradiance from each source as both the response curve and the distribution of radiation from both sources are constant. Because the design of the system allows for the determination of the measured incident radiation due to the artificial source, the contribution to the sensor reading from natural light can be determined and thus the total sensor response can be decomposed into artificial and natural contributions. With the sensor response decomposed thusly, the contribution of each source to the human eye response can be evaluated similarly. For a commercial system it would be preferable to select a sensor more closely tailored to the visible light spectrum or incorporate light filtering films to the design of the sensor itself to address the variable spectral distributions of reflected light; however, for use in the laboratory test bed where the largest portions of measured light are direct light components this decoupling procedure is deemed sufficient. In order to determine the visible light contributions from the two sources, transformation factors are calculated. These factors are evaluated by comparing the numerical integral of the original emittance and spectral power distribution curves with the product of these curves and the relevant response curve. By comparing the results from the photopic curve and sensor response curve computations, the measured sensor response can be converted to the equivalent visible spectrum value. Using the response parameters for the selected sensor, the luminance value is computed using Equation 3-1. [3-1] D/A Module The hardware design for the digital-to-analog (D/A) converter enables direct and robust software implementation. The eight pins on the Atmega64 port C are connected in parallel with the eight input signal pins on the D/A allowing the port C pins positions, when initialized as digital output pins, to function as the bits of the control signal. The desired light level fraction is converted to a fraction of the maximum value represented by the eight bits, 255, and this value is written to port C.
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