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Let There Be Light: What a Grower Has to Know About Light

Discussion in 'Indoor Growing' started by bcnl_joyce, Nov 4, 2014.

  1. bcnl_joyce

    bcnl_joyce Administrator Staff Member

    Light is one of the most important things for a growing plant. If you want your plants to stand a chance at all, you need good lighting. So, why is light so damn important?

    It’s called photosynthesis. This is why your plants need light. Photosynthesis is the process where plants take light energy, usually from the sun, and turns that into chemical energy—the energy stored in the bonds of chemical compounds (i.e. atoms and molecules).

    When a chemical reaction happens, heat is usually one of the byproducts. This means that the energy created by a chemical reaction is its chemical energy.

    Plants use chemical energy to create other chemicals that help create fresh “tomatoes.”

    So, that’s easy enough. How plants absorb light, though, is a whole other ballgame, and quite complicated.

    First, we need to understand what a “lumen” is.Lumens is a unit of luminous flux, the measure of the perceived power of light. It’s a way to figure out how much power we think a light source emits.

    It measures the total “amount” of light emitted by a source that’s visible to us (i.e. that we see), and describes the amount of light that is radiated by a source.

    A good way to illustrate this is through candles, because, you know, light.

    Picture one candle. We’ll call that one lumen. Now picture a thousand candles lighting up a 1,000 square-foot area. This means that it takes a thousand lumens to light up a thousand-square-foot area.

    That’s exactly what lumens are—one single candle’s worth of light, per square foot. The other requirement of a lumen is that it’s held one foot away. So, one lumen is worth an x amount of light when held one foot away.

    One lumen equals 10 lux. The term “lux,” though, is usually used to describe the amount of light energy actually reaching a surface. This is also known as “illumination.”

    This all adds up to light intensity. The higher intensity of your light, the more your plants grow. That’s the bottom line.

    The higher the wattage, the higher its intensity and the quality of light it emits. And, like we just learned above, we want a grow lamp that’s high in lumens.

    But there’s a bit more to that. The number of lumens is actually rapidly plummeting from when the light is emitted from the lamp, to when it reaches your little baby’s leaves. It’s called the Inverse-Square Law.

    Know this before you proceed: when the light source is closer, the light is brighter. When the light source is farther away, the light is less bright.

    The Inverse-Square Law states that the magnitude, or strength, of something is inversely proportional to the square of something else.

    What all that means is that the closer the light source, the brighter/better/more intense the light.

    Say you have a light shining on a single square foot from a square foot above whatever you’re shining it on. Let’s pretend that light equals one lumen. Move that light two feet, and the lumen is reduced to a quarter of what it once was (so, you now have ¼ lumen).

    The lumen has reduced because it’s got a farther distance to travel to cover a larger surface area.

    So, to sum it up: plants grow faster and stronger when the grow lamp is closer. That’s why BCNL grow boxes position the light source two-and-a-half feet away from your plants. You know, optimal growth and all.

    Light penetration is also something to keep in mind, as double the light, does not equal twice the penetration.

    Penetration is important because you want the very core— roots and all—of your plants to get that good stuff from your light source to encourage photosynthesis, which means more growth.

    This is why having a huge grow box may not be the most efficient thing. Tall plants mean that the lights have to be placed higher up. This increases the distance between the light and the plants’ roots. Less light, less plant growth.

    Last thing to understand: the light spectrum. This is that ROY G. BIV stuff.

    ROY G. BIV is the varying wavelengths of light spectrums. Blue is at about 400 nanometers, and red, on the other end of the spectrum, is at about 700. This is what your eyes see as different colors.

    Depending on what stage of photosynthesis your plant is in, the plant will absorb different colors, in varying amounts.

    Just like what your diet should be like, your plant needs all the colors of the rainbow. This is because a plant’s growth is separated into two phases: vegetative growth, and root growth and flowering.

    Vegetative growth requires the blue end of the spectrum (420- 550 nm). Root growth and flowering requires yellow, amber, and red from the spectrum (550-750 nm).

    Now bulbs. There are two major types of bulbs: LED lights and HID lights.

    For the most part, LED lights sit mainly in the 400-600 nm end of the spectrum. This means that LED don’t have flowering power, or at least as much as HID lights.

    There are two types of HID lights: metal halide, which covers the blue end of the light spectrum, and HPS, or high-pressure sodium, which covers the red end.

    In sum, this is what you need to know:

    1. Plants like a lot of light.
    2. Light sources should be placed closer, rather than farther, from your plants.
    3. Light penetration is most efficient when your plants aren’t massive so its roots can get that good stuff from the light source, too.
    4. Your plants need the entire spectrum of vary wavelengths because rainbows are awesome.
    5. HID has more flowering power than LED lights.

    Can you think of anything I missed? What else is important in regards to lighting that every grower should know?
    OneSlayer likes this.
  2. OneSlayer

    OneSlayer I Have The Munchies

    Thanks for the info.
    There is a lot of places to get this kind of info.
    It's nice to have it here.
    This forum is getting to be one of the best places to get all the info we need.
    Nice work on the forums
  3. Todd

    Todd Member

    Would there be any problem with using a HPS bulb in Vegetative instead of flower? Just Curious...
  4. Newbie Doobie

    Newbie Doobie Free Old Hippy

    Not recommended, wrong spectrum of light for vegging
    Todd likes this.
  5. Farmer J

    Farmer J @onelunggrows

    You can use it, might have elongated internodes
  6. Todd

    Todd Member

    The reason i ask is that when im doing anything with clones or vegging in the veg chamber, i take my MOTHER out and put it in the light from the flower side and i don't want to mess things up like having it Hermie on me. I also open my bloombox when im home so as to cool my box down. Closed, its up around 78=80 with the front doors open I'm down around 70=72 so i do this whenever i can! Any advice or someone chiming in would be GREAT ! Thanks guys!

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