The Kelvin Color Temperature Scale is a measurement of discriminating colors for the human eye. Color temperatures over 5.000K are called cool colors (blue/white), while lower color temperatures (2.700–3.000K) are called warm colors (yellow/white through red). This is a measurement for the human eye, but serves as a reference for helping consumers know which lamp to buy, for which stage of growth. OCL Digital Lamps have been developed for living things; plants, people, reptiles, fish etc. Traditional lamps were made for human vision and relied on peaks of energy for the human eye. OCL understands not all growers can budget four lamps for every fixture, so the “one lamp system” means the 4K can be used for all stages of plant growth if needed. Your plants will get more photochemical reactions with an OCL digital lamp than could be achieved with any traditional lamp that was made for human vision. HPS – recommend for the majority of flowering when growing annual plants. 4K – this is a full spectrum light, good for all stages of growth.