The difference in the efficacy of the varied color spectrums of light on actual photosynthesis is called the quantum efficiency curve, or yield photon flux (YPF) curve.

If you take measurements using a standard quantum flux meter under a lamp that generates only blue light, you are going to get good PPF and PPFD values, even though blue light is less efficient at stimulating photosynthesis than red light.

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Not all lighting manufacturers understand how to properly measure and present light outputs for plant growth. As the label below shows, the lamp manufacturer included measurements of lux, but no PPF information. In fact, the label mixes up PAR and lux measurements in an attempt to provide PPFD measurements at different distances from the plant. But, as you now know, lux and PAR are distinct measurements.

Unfortunately, far too many lamps include this kind of incorrect information.

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Lettuce is a great candidate for direct seeding. These seeds can be sown directly in the the final pot, without the extra step of transplanting. Be sure to read the seed packet for planting instructions.

After the seedlings germinate, be sure to thin them so they aren't overcrowded in the pot. You can then continue to grow your lettuce in the same container until harvest.

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The light produced from metal halide (MH) lamps looks white and bright with a cool visual temperature. While you can also use MH lamps during the flowering stages of growth, many growers employ them only when growing seedlings, cuttings, or vegetative transplants, or bulking up vegetative growth on larger plants.

MH Lamps generally emit a light spectrum range that closely mimics that of natural sunlight, weighted to the blue and violet spectrum, so they are good for all vegetative stages of plant growth.

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Multicolor white LEDs, also known as RGB LEDs, mix separate red, blue, and green diodes together in a balance to create white-colored light that is both visually pleasing and efficient for plant growth.

RGB LEDs are a bit more complicated to manufacture than standard white full-spectrum LEDs, so they may cost more.

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When most or all of the seeds germinate, you are confronted with a tiny seedling forest. It is tempting to let them all continue to grow, but your seedlings will be better off if you cull the weakest ones.

After your seeds have sprouted, choose the strongest, stockiest seedling in each cell and snip the remaining seedlings at the base. Throw the excess seedlings on your salad or feed them to any critters who would appreciate some greens.

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There are plenty of low-light tropicals and blooming plants that you can grow successfully indoors with good ambient light, and you can maintain certain light-loving succulents for a while in a windowsill.

But even a bright windowsill is typically not the right location for plants you intend to harvest for food. The same goes for heavy-blooming plants. Reproduction is an energy-intensive process. Producing flowers, fruit, and seed requires a lot of juice. Plants need enough light, and the right kind of light, to get the job done.

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HPS lamps were the most common type of plant lighting in greenhouse growing operations until LEDs gained popularity. They are used primarily for supplemental lighting where natural sunlight (more blue light) is also present, such as in a glass or poly greenhouse. HPS lamps are also used to extend photoperiod.

Their light spectrum is heavily weighted to yellow, orange, and red, with only very small amounts of blue light, which is why they are used for supplementing ambient natural daylight.

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