First of all, dual wavelength low coherence light source is not necessarily a modern light source. For example, Molnar and Tutsch created a dual wavelength low coherence light by combin- ing a conventional broadband light source and a He–Ne laser with a wavelength of 632.8 nm [21]. Secondly the hybrid light sources in Heikkinen et al.’s work is made out of two monochromatic LEDs [19]. On the other hand, the intensity spectrum of super- continuum light source (which is an example of modern low coherence light source) is similar to the conventional light source [17,18], and there is no distinctive feature in its corresponding interference signal.