Alot of people ask my what the difference between spectrums are, here is an image of some common spectrums used in lighting, and below is a list of the spectrums we currently use and what they are good for.
3000k - Flower
The 3000k light is ideal for flower cycle only, this light has a lower kelvin(k) value indicating a "warm" light, this means that it has extra red light in its spectrum making it ideal for mimicking the sun during the flowering stage of a plants lifecycle, these lights are ideal for flowering only,
3500k - Full Spectrum
The 3500k light is ideal for both flowering and vegetative growth, hence the name spectrum, this light is the jack of all trades, this is ideal for beginners where you use one light for all aspects of your crop development and for certain types of plants and produce, these can be used for mothering, cloning, vegetative and flower phases.
4000k - Vegetative
The 4000k light is ideal for the vegetative phase of a plants growth, this light has a higher kelvin(k) value, indicating that it is a cooler, or more white light, this in the LED's translates into more blue spectrum which is what plants would typically experience during spring when the plants are growing, these are ideal for mothering, cloning, and vegetative development
Here is a image demonstrating how different light sources produce different spectrums