Will the spectral distribution change after the brightness is reduced?

The change in brightness usually does not alter the spectral distribution of the light source, but this conclusion needs to be analyzed in combination with the specific type of light source and the dimming method:
Theoretical basis
Spectral distribution reflects the relative intensity of light at various wavelengths, which is an inherent property of the light source. Brightness adjustment is mainly achieved by changing the total optical power, such as adjusting the current and other methods. Theoretically speaking, during the process of brightness adjustment, the proportion of light of each wavelength should remain unchanged. For instance, in the case of an ideal LED, when PWM dimming is used, it merely controls the brightness through rapid switching. Under this dimming mechanism, its spectrum remains completely unchanged, and the proportion of light of each wavelength always remains the same. For instance, high-quality lamps, in their design, will optimize multiple factors such as circuits and materials to ensure that the spectrum remains consistent under different brightness conditions. Whether in high or low brightness states, they can display stable and expected spectral effects.
Exceptional circumstances and precautions
However, in actual situations, there are also some exceptional cases that need attention. In terms of thermal effect influence, for instance, when an incandescent lamp is dimmed, the temperature of the filament will decrease accordingly. This temperature change can cause a redshift in the spectrum, meaning the color temperature will drop. This clearly indicates a change in the spectrum. For leds, some leds may experience slight spectral shifts when operating at low currents due to changes in the efficiency of the phosphor or the characteristics of the chip itself. For instance, the color temperature change may be less than 100K. Although the variation is relatively small, there is still a situation where the spectrum changes. In addition, in terms of composite light sources, taking RGB mixed light sources as an example, if the responses of leds of different colors to current changes are inconsistent, then during the process of brightness adjustment, the mixing ratio among them may change, thereby affecting the overall spectrum and causing it to change.
Safeguard measures in practical applications
In the professional lighting field, there are corresponding safeguard measures to ensure the stability of the spectrum. For instance, in places with strict lighting requirements such as museums and photography studios, the lamps used often have strict color rendering index (CRI≥95) requirements. To meet such high standards, a combination of constant current drive and PWM dimming is adopted. Through this scientific combination of dimming and drive, the stability of the spectrum can be guaranteed to the greatest extent. Meet the demands for accurate color reproduction and other requirements in professional scenarios. In terms of display calibration, high-end displays will employ the technical means of dynamically adjusting the color matrix at low brightness. The main purpose is to compensate for the changes in human perception in this environment, rather than altering the spectrum itself, thereby ensuring the accuracy and comfort of display effects at different brightness levels.
Experimental verification data
The data obtained from the test of a certain brand’s 5000K LED also confirm the relevant situation. When the brightness gradually decreased from 100% to 10% (simulating the dimming process), the color temperature change only reached 32K, which was approximately 0.6% when converted to ΔCCT. Moreover, the shape of the spectral curve remained basically consistent without significant changes. Especially when the PWM dimming mode is used, the color temperature change is less than 5K. There is no significant difference in the spectral distribution both visually and in actual detection. This further indicates that under the appropriate dimming mode, the influence of brightness adjustment on the spectral distribution is extremely small.
Conclusion: In most modern lighting scenarios, brightness adjustment does not significantly change the spectral distribution. However, in fields with high-precision color requirements (such as printing color calibration and film and television shooting), it is still necessary to choose light sources with spectral stability certification and avoid using dimming schemes that rely on color temperature adjustment.