Usually the dimming of a light source is done by changing the voltage of the power supply.
In this case the spectral distribution emitted by the lamp is changing towards a more reddish spectrum when reducing the voltage. If the dimming is done by a mechanical shutter which is brought into the ray the illumination level changes, but the spectral distribution stays nearly constant over a wide range of illumination levels.
The blue, orange and yellow curve are describing the spectral distribution at 12 V, 10 V and 8 V of voltage at the lamp.
The blue, green and red lines are showing the spectral distribution at full power (2600 Lux) and dimmed to 1000 Lux and 10 Lux.
The different spectral distributions were normalized to a value of 1.0 at 555 nm.
The correlated color temperature was measured with a Spectrascan PR650.
The spectral distribution was measured with an Ocean Optics HR4000.
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