Why taking culture OD at 660 NM?

Answer 1

see od measures the light scattering and light scattering inversely varies with the wavelength. So smaller wavelength say 430nm would be more sensitive than longer wavelength say 660nm but here we take od in LB media and yellow colour absorbs shorter wavelngth so to obviate the error due to absorbance we take od at 660nm. -Satya Pal Arya

Answer 2

Culture optical density (OD) is measured at 660 nm because this wavelength is commonly used to quantify the turbidity of the culture, which correlates with cell growth and biomass production. By measuring OD at 660 nm, we can quickly and easily monitor the growth of microbial cultures without having to wait for lengthy biochemical assays.