I know that LED bulbs can vary along two important dimensions, lumens and "temperature." In particular, the temperature is important to make sure the plant gets the frequencies of light it needs. One source I read said
As a general recommendation, choose a full spectrum grow light with a color temperature in the blue range (5,000 - 7,000K) to promote vegetative growth and choose a color temperature in the red range (3,500 - 4,500K) to promote fruiting and flowering.
This source goes on to say
Many grow lights are labeled as "full spectrum," meaning they emit light across the full-color spectrum, including not only blue and/or red light, but also enough green light for the overall output to look like natural light to the human eye. While plants primarily use blue and red light, research suggests that some species perform best with full spectrum light. Therefore, it can be helpful to choose a full spectrum light.
I am confused by a couple things:
- How do I tell whether a given species of plant needs full spectrum, red, or blue light?
- I thought white light is a combination of all colors of the spectrum. Why wouldn't that be sufficient if it carries all of them?
- They sell "grow lights" online, some of which have "full spectrum", "red" and "blue" bulbs all together. But they are obviously much more expensive then just buying a single bulb. Are there any disadvantages to first identifying my plants need and then choosing the bulb type it needs? For example, suppose my plant needs red light, wouldn't it make sense to buy a red bulb instead of a grow light?