For indoor plants, green light is the least effective for growth because plants reflect green light rather than absorb it. Red and blue lights are better as they support aspects of plant development like leaf growth and flowering.
If you are considering which colored light bulb is the least effective for your indoor plants, the color green would be the least effective. This is because plants typically look green due to chlorophyll, the pigment primarily responsible for photosynthesis, reflecting green light rather than absorbing it. Red and blue wavelengths are very important; blue light is responsible for leafy growth, while red light affects flowering and fruiting.
Based on the information given and knowing that plants use chlorophyll a and b for photosynthesis, which absorb light primarily in the red and blue spectra, green light is less effective for plant growth. Red and blue lights are more beneficial to plant health and growth. Therefore, when buying a colored light bulb for your plants, green would be the color to avoid if you want to support optimal plant growth.
So, for the purpose of indoor plant growth using colored light bulbs, green light is the least effective and should be avoided in favor of red or blue light, which are necessary for different aspects of plant development.