LED Test Array 3 x 30
The earlier test used discrete color LEDs (red, green and blue). The current crop of white LEDs (actually blue emitters with a yellow phosphor doped into the encapsulation) have a distinct blue tint. This test works under the premise that the true white part of white LEDs is quite useful while the ‘blue disturbence’ can be corrected with green and red to control the color temperature of the resulting light.
Three assemblies were made, with 30 white, green and red LEDs. The arrays were then mounted such that their beams converged on the target some 30 inches away. the sketch to the left shows this layout, albeit not to scale.
It should be clear from the sketch that the target will not show a uniform color. However, the test will be used to investigate whether desirable white light can be obtained in the center portion where all three beams converge.
The white LEDs have a strong bluish tint. The idea is to investigate whether the red and/or green arrays can correct this into a more pleasing warmer white.
The photo to the left was taken by aiming the camera at an angle toward the lights. A sheet of translucent vinyl covers the the LEDs to avoid blinding the camera
By driving the white LEDs at full power and adding small amounts of red and green, the color temperature at the center could be adjusted nicely. However, there were distinct colors over a wide area of the beam outside the center. The wider beam spread of the red LEDs caused a red halo at the perimeter of the entire target pattern (not shown here).