Grow Lights – Different Types, Sizes, Shapes, Pros and Cons

Why do we even care about light?

Because light is ESSENTIAL for photosynthesis. Photosynthesis is the process by which ‘light energy’ is converted to a ‘chemical energy’ that can be used to fuel cellular functions. Without light, there would be no photosynthesis, there would be no chemical energy and there would be no plant growth :cry:

2 CRUCIAL things about getting the light right

  1. Get the spectrum right
  2. Get the intensity/brightness right

The right spectrum – Photosynthetically Active Radiation (PAR)? Kelvin or Nanometers? WTF!?!

ANY light is NO GOOD for plants. The light spectrum is measured using either degrees Kelvin or in nanometers as shown below. Regardless of how you measure it, only a certain part of the whole spectrum is efficient in inducing photosynthesis. This portion of the light spectrum is known as “Photosynthetically Active Radiation” or PAR.

You will see that the light spectrum is referred to using 2 methods. It can be confusing. Some grow light manufacturers say “Our bulbs produce 5600 0K light” while others say, “Our bulbs produce 450 nm light”. Excuse me ?!#@ Let us try to explain that in ENGLISH!!

  1. Color temperature – measured in 0Kelvin.

    Grow lights color temperature in Kelvin

    Image credits:

  2. Wavelength – is measured in nanometers (nm) Visible color spectrum
  • Blue light is best for growth/vegetative phase of plants
  • i.e. >5000 0K or 400-500nm light emitting bulbs
  • Red light is best for flowering phase of plants
  • i.e. 2000 – 3000 0K or 600-700nm light emitting bulbs

You can’t have either RED or BLUE throughout. You will have to change bulbs according to the growth phase unless you buy something like this which has 3 colors of bulbs

The right light intensity

There are a LOT of misconceptions about light intensity among amateur hydroponic farmers. Let’s try to address some of them here.

  1. Light intensity is measured by ‘lumens’ (abbreviated ‘lm’) – Correct
  2. The best measure of a grow light’s ability to regulate photosynthesis is not PAR watts, not lumens, not lux, but watts – Wrong – Lumens, Lux, Watts etc. are all measurements based on how the human eye perceives light intensity. This cannot be applied to plants. For example 100,000 lux of 4000 0K light does no good to a plant’s photosynthesis because that color temperature does not belong to the range of PAR (Photosynthetically Active Radiation). 1,000 lux of 5600 0K light would result in a lot more photosynthesis than 100,000 lux of 4000 0K light. Therefore, actually, the best method to measure a grow light’s ability to induce photosynthesis is using PAR watts. A 400 watt bulb that emits different spectra of light may emit 150 PAR watts worth of light. This 150 watts is what actually matters for plant growth. However, grow light manufacturers do not currently include PAR watts on the packaging and there isn’t a light meter that can measure PAR watts. So even though it’s not the most accurate way, we’re going ahead using lumens and lux to explain light intensity.
  3. A bulb emitting 1000 lm would result in higher photosynthesis than a bulb emitting 500 lm – Depends – lumens measure TOTAL amount of light. That includes red light, blue light, orange light etc. etc. If both bulbs above produced the same type of light e.g. blue light, 1000 lm would result in more photosynthesis than 500 lm. An LED bulb producing 500 lm of 5600 0K light would result in more photosynthesis than would an incandescent bulb emitting 1000 lm of 4000 0K light any day! This is why lumens from ANY bulb is not good for plants growers.
  4. A bulb emitting 1000 lm of 5600 0K light would cause more photosynthesis than a bulb emitting 500 lm of 5600 0K light – Correct
  5. A bulb emitting 1000 lm of light consumes more electricity than a bulb emitting 500 lm of light – Depends – what turns your electric meter is NOT lumens, but watts. To produce 1000 lm of light, you only need a 10 watt LED bulb. But you may need a 200 watt incandescent bulb to produce 1000 lm of light.
  6. A 100 watt bulb consumes more electricity than a 50 watt bulb – Correct
  7. A 100 watt (w) bulb produces more lumens than a 50 w bulb – Depends – LED bulbs and HPS bulbs are more efficient in generating lumens from watts than most other types of bulbs. For example, an LED or HPS bulb could produce over 100 lumens from each watt. In contrast, an incandescent bulb may only produce up to 20 lumens per watt. So a 50 watt LED or HPS bulb would produce over 5000 lumens of light while a 100 watt incandescent bulb would only produce a maximum of 2000 lm. This is why the given statement is not always correct.
  8. A 100w LED bulb produces more lumens than a 50 w LED bulb – Correct
  9. A 1000 lumen LED bulb placed a few inches above plants cause the same amount of photosynthesis as a 1000 lumen HPS bulb placed 2 feet above the plants – Wrong – High Intensity Discharge (HID) grow lights like High Pressure Sodium (HPS) and Metal Halide (MH) produce a lot of heat. Therefore, they need to be hanged anywhere from 6 inches to 4 feet above the plants depending on the wattage of the bulb. So even though an HPS lamp produces 1000 lumens, the plants won’t get all 1000 lumens of light. The further away the lamps are from the plants, the fewer the lumens that reach the plants. In contrast, LED lights do NOT produce a lot of heat and can be placed just a few inches over the plants. So the ‘loss of lumens’ from the surface of the bulb to the plants is minimal. So a 1000 lumen LED bulb hung 3 inches above the plants would cause more photosynthesis than a 1000 lumen HPS light hung 1 foot above the plants. We don’t want to go in to detail here, but the intensity of light falling on a surface is measured by lux (of foot candles) rather than lumens. The principle remains the same, the plants get a lot less lux of light as the lamp is lifted farther away from the plant. The best way to measure the light intensity in lux is to get one of these cheap Lux meters.
  10. A 100w LED lamp producing 56000K (same as 450-460nm) light produces more lumens than a 100w metal halide lamp producing 56000K lamp – Correct
  11. A 100w LED lamp producing 56000K light causes more photosynthesis than a 100w metal halide lamp producing 56000K lamp – Correct
  12. A 100w LED lamp producing 56000K light is cheaper on the electric bill compared to a 100w metal halide lamp producing 56000K lamp – Correct – the electricity consumption is the same; however, the LED lamp produces >10,000 lumens of light while the metal halide lamp produces about 5000 – 7000 lm. So the LED lamp causes more photosynthesis and more vegetative growth for the same electric cost!

Take home message about light intensity

  • Watts and lumens of a grow light are important factors to consider.
  • But direct comparisons don’t always make sense from a plant growth point of view.
  • A 100 watt bulb doesn’t always produce more lumens than a 50 watt bulb – different types of bulbs produce different amounts of lumens per watt
  • A 10,000 lumen lamp doesn’t always result in higher photosynthesis than a 5,000 lumen lamp – it depends on the wave length of light it produces and the height at which they’re hung above the plants.
  • The absolutely correct way of measuring light intensity beneficial to photosynthesis is to use PAR watts. However, manufacturers don’t include this information on grow light packaging and there are not PAR watt light meters. So there really isn’t a straightforward way of measuring PAR watts from a particular grow light.

Different types of grow lights (aka plant lights)

There are different ways of categorizing various grow lights available. One of them is given below.

  1. LED grow lights
  2. Fluorescent (CFL; compact fluorescent lamp) grow lights
  3. Incandescent grow lights
  4. High Intensity Discharge (HID) grow lights
    • High Pressure Sodium (HPS)
    • Metal Halide (MH)

What’s the BEST type of grow light?

Unfortunately, there isn’t a Black and White answer to that question. LED grow lights may be better than HIDs in one aspect, but HIDs are better than LEDs in another aspect. There isn’t (yet) a perfect grow light. The consumer has to decide which one suits his/her needs best. We have made the following table so that your making that decision becomes easier.

LED Fluorescent Incandescent HPS MH
Predominant color spectrum  Available in blue, orange and red spectra Generally blue; but now also available in red and full spectrum as well Red-yellowish (~2700K) Red (2200K) Generally Blue (>5000K). But now available in the 3000-4000K range as well
Best for Growing and flowering Growing and flowering Flowering: this spectrum of light triggers plant hormones that increase flowering/budding.  Growing. Leafy vegetables.
Lumens per watt (lm/W)* 110 – 160 60 – 90  5 – 20 80 – 140 50 – 70
Lumens produced by a 100w bulb* ~13,500 (highest efficiency) ~7,500 ~1,000 (lowest efficiency) ~12,000 (lower efficiency than LED) ~6,000
Average life span 100,000+ hours up to ~20,000 hours (~10,000 hours for CFLs) < 1000 hours up to ~20,000 hours up to ~20,000 hours
Heat generation Low Low, but produces more heat than LED lights HIGH HIGH
Height of hanging Few inches above plants > 2 feet 6 inches to >2 feet depending on wattage of bulb
Cost of bulbs Most expensive  Cheap Cheapest Cheap models available Cheap models available
Impact on the electric bill Least Most
 Special notes
  • Smallest, most light weight, least space occupying
  • Mercury-free, most eco-friendly
  • Most lumens of light per watt – thus most energy efficient
  • Least heat producing
 High-output lights producing 2-3 times more light as standard fluorescent lights are now available
  • Deficient in blue light; thus NOT good for vegetative growth
  • Very good as a supplemental light source for green houses where there is plenty of sunlight

* Lumens: Although lumens is the standard way to measure light intensity, it is not the best way to measure the effectiveness of a particular type of grow light on plant growth. For example, a bulb can produce 1000 lumens of 4000 0K light and that is useless because plants cannot do photosynthesis efficiently with that spectrum of light. So if you want to use lumens to compare 2 types of bulbs, they have to be producing the same wave length of light. A proper comparison would be a 5600 0K LED vs 5600 0K HPS. If the LED produces 100 lumens per watt and the HPS produces 80 lumens per watt, you can confidently say that the LED is more efficient, as a grow light, for plant growth.

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