For understanding this, you need to understand the basic concept of ‘light’. Light, basically, is composed of wavelengths of various color but we usually think it to be yellow or red. However, a closer look at the various wavelengths tells you that you require lights of warm as well as cooler wavelength to ensure a good growth of your seedlings. Hence, the best grow light for seedlings always has red and blue lights (at the least). While a full spectrum grow light is recommended, having red and blue lights are your minimum requirement.