The prefect light scale for a plant depends on the colour of its leaves. A plant with colour of sea green leaves like medical marijuana will imitate green beam (a clever trick to remember if you ever need to enter your grow room during the dark phase — use a green light for your plants, it will still look pitch black). For green-leaved plants, the ultimate light spectrum (called “the action spectrum”) peak with violet-blue and red, which is one reason why an increasing number of plant growers are choosing to use LED lights, where we can set the individual bulbs to imitate whatever light spectrum we wish.
However, the most important grow bulbs are still Metal Halide (MH) and High-Pressure Sodium (HPS). Manufacturers of these bulbs do their best to copy the light spectrum of natural sunlight.
However, not all Metal Halide grow light bulbs (MH) and High-Pressure Sodium (HPS) grow light bulbs are created equal. Growers may try to purchase low-cost bulbs from China or elsewhere to save money, and who could blame them? For hobbyist growers who are just being started and have limited money, low-cost bulbs like Metal Halide (MH) and High-Pressure Sodium (HPS) can be a decent option, but don’t expect record-breaking yields.
For professionals, a superior bulb, ballast, and light hood will make a foremost differentiation in the health & size of your yield. We also recommend replacing your grow light bulbs every few grow phases because they will go down with use. Those grow light bulbs are full of gasses, which shift around and don’t react the same after a year as they did on first day.
Typically, this weakening will noticeable itself by lumen loss — your once-bright bulbs will become dimmer and dimmer before they finally expire. However, just because your grow lights are dimmer doesn’t symbolize your ballast is outputting any less energy, so you may be out paying for 1000 watts of grow light, getting significantly less from your grow light bulb.
Now that you have a little more education about photosynthesis and light spectrums, you should be able to get out there and maximize your harvest.
Good Luck and Happy Growing!