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Enlighten Me!

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There is a wealth of information out there on indoor lighting, PAR, Lumens, Spectrum, LUX, Wattage, HPS, T5, LED, etc., etc.. It can get confusing, making it hard to determine what type of light is required for your specific growing needs. We’ll break it down for you in order to make it more approachable and easy to understand.
Light, traditionally the kind from the sun, is primarily responsible for the photosynthetic process in all green plants. The byproduct of photosynthesis is oxygen and glucose (food). Simply put: Light = Plant Energy & Oxygen.

Photosynthesis consists of two cycles: Light and Dark.

During the light cycle, different wavelengths of blue and red light stimulate various plant functions from growth rates, flower formations, oil and scent production to the actual structure of the plant. But what wavelengths do what specifically? Luckily, some very smart people figured this out for us and we’ll go over that shortly.The better quality of light and the more leaf area exposed, the better the energy production, enabling the leaves to create and store as much energy as possible, as quickly as possible. This glucose energy is stored in the leaves throughout the whole plant. So take care when trimming those lower leaves, you may be removing possible “energy banks”.

When the plant has created and stored as much energy as it can, its “energy banks” are full. Anymore light after this time is potentially wasted. Enter the dark cycle. In this cycle, plants convert the glucose into more complex sugars (energy). Think of this process as digesting light. This is an important job, but the dark cycle still has more work to do.Plants are effected by the length of time that they are in darkness, not light. This is referred to as the photo period. The length of the photo period triggers a hormonal response that makes them want to reproduce (flowering/fruiting). So if we can control the length of time that a plant is exposed to darkness, then we can control its hormones… if only this was possible in teenagers.

Now, every plant is different, but most fall into 1 of 3 categories: Short Day, Long Day, and Day Neutral. It’s important to know which category your plant falls under when you’re programming your light timer. We don’t want that spinach to bolt, now do we?

Spectrum: The reds, the blues …

The light energy available to plants is determined by the color and intensity of the light. First up is color or Photosynthetic Active Radiation… sounds intense right? Commonly known as PAR, it’s the wavelength range needed for photosynthesis. If your light is not in the correct blue & red area of the spectrum, then no plant energy is created. Blue light promotes better plant structure with stockier stems and shorter inter-nodal length. Red light promotes flower growth, however, a combination of both is best when flowering/fruiting. This is not to say these functions cannot happen outside of each spectrum, but who wants sub-par plants? I sure don’t.


Photo ©Sunmaster Grow Lights

But what about the actual lights??!!

Fluorescent grow bulbs have been a very popular grow light for a number of years. Now, you could use those larger shop-type bulbs available at every home improvement center, or you could get a sleeker, sexier, high output T5 fluorescent grow bulb. Optimized for plant growth (remember PAR), more efficient and with light uniformity from end to end, it’s a gentle light whose low heat and minimal energy costs make it ideal for a wide range of applications. You can get it within millimeters of the leaves without fear of burning your plants. From seed starting & supplemental lighting to all out love-me-some-greens multiple bulb fixtures, T5s can work for you.
The biggest drawback for T5s is that they don’t really have much intensity. Once your plants get above 12 inches, the lower leaves aren’t getting enough light and the top ones aren’t getting enough intensity to fill up all those important “energy banks”. Therefore, T5s are best for baby plants, leafy greens and supplemental lighting.

Want more light intensity? 

Then you have to step up to a big, powerful, bad-ass  High Intensity Discharge (HID) lamp. We know HID doesn’t really sound as cool as PAR, but we’ll take it. An HID system consists of 3 main parts: a ballast, reflector, and lamp.The reflector focuses the light in the preferred direction, making the light more efficient. They come in various shapes and sizes depending on how much area you want to cover. Always, always use a reflector.

The ballast is the driving force of the lamp, sending and controlling energy. It’s like the engine behind the bulb, without it no HID bulb can spark.


HID ballasts come in three different flavors:

  • Magnetic: These tanks were the original ballast, but run very hot and noisy.
  • Electronic: Produces less heat & is 400x more efficient, but won’t save energy costs.
  • Digital: Like an electronic ballast on steroids, it can actually communicate with the lamp.  Continually monitors the output to the bulb to prolong its spectrum, brightness and lifespan.



And now for the bulbs themselves…

  With intensity of 250W, 400W, 600W or 1000W, HID bulbs have you covered throughout the whole grow cycle.  Most current HID bulbs will work on both an Electronic or Digital Ballast, just make sure that you’re getting a ballast that has enough wattage for your new, super powerful grow lamp.

And to make it even more confusing there are two types of lamp to choose from when choosing your HID bulb, Metal Halide and High Pressure Sodium. Make sure you’re using the correct one for your plant’s current growth stage.


Metal Halide (MH)

Use during Vegetative growth
Promotes Strong, Healthy Stems & Leaves

Imitates Daylight

Runs Hotter than HPS


High Pressure Sodium (HPS)

Use during Flowering
Enhances Fruit/Flower Production

Imitates Autumn sun

Appears yellowish


Of course, there are some drawbacks to HID lighting. A 1000W bulb can suck power from your house faster than a mosquito draining blood from a baby. HID bulbs also run very hot… like burn your plants hot. So please keep them 10-16 inches from your plants at all times. If you’re unsure how far, put your hand on top of your plants. If it’s too hot for you, it’s definitely too hot for them.You should replace your HID bulb every 60k hours, or once a year if used throughout. They tend to degrade over time, and your eyes may not notice a difference in the PAR spectrum, but your plants will. Keep it as a backup in case you run into an emergency situation.

While these are some of the great grow light options available to the home gardener, there are still more to explore. Demand and technology have opened the doors for LED, Ceramic MH, and Double Ended lighting options, but we’re going to save those for another day… In the meantime, enter your own dark cycle and let your brains digest all of this delicious information.


Image source: State of Green http://bit.ly/1oF6J2F