■ Because (high-end) LEDs offer a complete spectrum in which the most important wavelengths (expressed in nanometer, nm) are represented. For example: HPS lights mainly emit colors that are least favorable / effective for plants like yellow and orange light.
■ Improved light spectrum, specifically designed
■ Excellent fruit quality with more terpenes, giving a better effect, (fruit)color, aroma and taste compared to HPS, LEC, CDM, CMH or Plasma lights
■ Boost active substances and increase plant specific characteristics
■ Higher value crop harvests due to improved quality
■ More usable light, less heat than HPS, improved grow room conditions. Grow all summer long!
■ Less energy consumption, lower running costs compared to HPS and reduced cost on cooling/air conditioning (HVAC)
■ Silent and maintenance free with hardly any loss of light intensity during product lifetime
■ 50.000+ hours guarantee. No replacement bulb costs ever
■ Safe to use and easy to grow with

To ensure that your investment in an LED grow light meets your cultivation and production goals, you need to know what manufacturers mean by PAR, PPF, PPFD, and photon efficiency to make an informed purchasing decision. However, these three metrics should never be used as sole variables to make a purchasing decision.

There are several other variables that need to be considered as well, we will explain these later on:

■ your goal: Are you germinating (seeds), are you growing seedlings, cuttings or mother plants; do the crops remain in the vegetative phase, or do they flower as well? Do you aim for the highest yields possible or do you have medicinal purposes in mind (we recommend spectrum control for the best medicinal endproducts)? The plantphase will mostly determine your final choice. Please read a more detailed explanation in section 3.
■ coverage area: The size of the surface that you want to illuminate used to determine the required wattage (to a large extend). Wattage used to tell you ''how much light'' would be emitted. This is not the case with LEDs (and lighting sources in general) as PPFD tells you how much usable light is actually emitted on the surface of your plant(s). Please read a more detailed explanation in section 2.
■ the spectrum: Determines for what kind of plant(s) and for which phase(s) of the(se) plant(s) the fixture is best suited (for Germination, Clones, Motherplants, Vegetative and/or Flowering). Every wavelength / color has a different effect on plant development and photosynthesis. Plants are in need for different wavelengths / colors in different phases (germination, cloning, vegetative and flowering) and ratio's. Please read a more detailed explanation in section 3 or the complete information here: https://ledbypassion.com/spectrum.
■ your personal health: Does your health allow you to work on your knees, to bend and to ''SCROG'' for example? Does it allow you to lift heavy lights (15 – 20 kg) or do you prefer to work with lightweight LED bars?
■ your growing method: We recommend different lighting systems for several growing methods; some LED systems need to be used at a close hanging distance (the distance from your light to the top of your plants) and other lights are used at a high hanging distance. So it depends on the method of growing you prefer.
■ your grow environment: Temperature, humidity, air circulation, background noise and your living situation for example (HVAC) can influence your final choice. For example: you don't want any noise (caused by active thermal management) if you are growing in your bedroom.

All factors need to be taken into consideration to select the most appropriate system based on your cultivation and business goals, and the take home message is that PPF, PPFD, and photon efficiency are the proper metrics used by scientists and industry leading horticulture lighting companies. If a company does not provide you with the correct metrics used for horticulture lighting, they should not be selling horticulture lighting systems, and you will not be able to verify the true efficiency of their system.

Space availability is a vital factor when purchasing lighting as it determines the amount and size of lamps you need. The first thing you need to do is measure the exact size of your garden. Then you need to find out the coverage area of the lights you're considering in order to determine the exact number you need. The recommended and maximum coverage area is mentioned in the discription of every light in our collection. The general guideline most growers use is that you need 32 watts of actual power per 30 cm² if you're growing high-light plants like tomatoes. Low-light plants like lettuce need somewhere between 11 and 18 watts per 30 cm².

We recommend different wattages for certain coverage areas, on average:

60 x 60 cm	50 – 200 Watts LED
80 x 80 cm	200 – 400 Wats LED
100 x 100 cm	400 – 600 Watts LED
120 x 120 cm	400 – 800 Watts LED

The recommended and maximum coverage area of a light are different in the vegetative and flowering phase because vegetative plants need a lower PPFD range compared to flowering plants. This means you can illuminate a larger cultivation area during VEG (because the hanging distance can be increased during the vegetative phase) in contrast to the Flowering phase.

This depends on the plant species and phase the plants are in. We recommend full spectrum LEDs for full cycle grows (a full cycle grow is a cycle from germination/vegetative phase to the reproductive/flowering phase). Full Spectrum lights are illuminaires in which most colors are represented: Blue/Violet, Green, Red and Far Red Light are essential. The addition of other colors of light (full-spectrum light) has been shown to have further benefits for plant growth. This can be done by adding wavelenghts from the UVB, UVA, Yellow, Orange and Infrared spectrum.

Although plants can grow under almost any type of light, efficient photosynthesis requires different wavelengths and some of the best led grow lights can provide plants with the full spectrum necessary throughout each growth.

For example, in order to grow most efficiently, many plants need light in the red, blue and green spectrums, but also infrared and ultraviolet, depending on the stage. A powerful full spectrum LED grow light enables you to cater to the plant's specific needs by providing the proper photosynthetically active radiation values.

Click here for detailed information about the Spectrum, Light and the effect of different colors / wavelengths on high-intensity plants: ledbypassion.com/spectrum

■ Germination (seeds): well-tuned (high) Blue to Red ratio and a small amount of Green, avoid Far Red
■ Clones (cuttings): well-tuned (high) Blue to Red ratio and a high amount of Green, avoid Far Red
■ Vegetative phase (including motherplants): Blue dominant, well tuned Blue to Red ratio and a high amount of Green
■ Pre-Flowering phase: well tuned Blue to Red ratio and a high amount of Green
■ Flowering / Reproductive phase: Red dominant, well tuned Blue to Red ratio and a moderate amount of Green
■ Ripen / Finish: - Last 3 weeks of Flowering / Reproductive phase: Supplemental lighting with UV-B wavelengths for 3-4 hours a day, in the middle of your 12 hour light cycle (the duration of this supplemantal lighting depends on your cultivation and business goals.
- Last 3 days of Flowering / Reproductive phase: ''No Red'' light treatment for Boosting terpenes in high-intensity plants (''Blue Light Treatment'').

If you have been researching LED horticulture lighting systems, you have likely been bombarded with a variety of metrics that lighting manufacturers use to market their products. Some terms and acronyms you are likely to see include: watts, lumens, LUX, foot candles, PAR, PPF, PPFD, and photon efficiency. While all of these terms do relate to lighting, only a select few really tell you the important metrics of a horticulture lighting system:

■ PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis.
■ PPF measures the total amount of PAR that is produced by a lighting system each second, in micromoles per second (μmol/s). This is probably the second most important way of measuring a horticulture lighting system.
■ PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second, in micromoles per square meter per second (μmol/m²/s).
■ Photon efficiency refers to how efficient a horticulture lighting system is at converting electrical energy into photons of PAR, in micromoles per Joule (μmol/J). The higher this number is, the more efficient a lighting system is at converting electrical energy into photons of PAR.

Click here for detailed information about these metrics: https://ledbypassion.com/lighting-metrics-par-ppf-ppfd-photon-efficiency

During establishment growth, light intensities need to be kept relatively low as the plant is developing leaves and stems that will be used to provide photosynthates during the vegetative growth phase. Increasing light intensity as you transition into the vegeta- tive and reproductive growth phases will increase the rate of pho- tosynthesis, which will provide the plant with more photosynthates used to develop flowers and subsequent fruit. Plants need time to adjust to high light intensities (referred to as photoacclimation). If you expose plants to high light intensities too early in the crop cycle, you can damage chlorophyll pigments causing photo-oxidation (photo-bleaching), so we recommend slowly increasing your light intensity as your plant develops. Refer to the recommended PPFD ranges for establishment, vegetative, and reproductive growth of high-intensity plants, tomatoes, cucumbers, and peppers.

■ Examples of recommended PPFD (μmol/m²/s):

Species	High Intensity Plants
Seed	100 – 300
Vegetative Cutting	75 – 150
Vegetative	300 – 600
Reproductive	600++

Species	Tomatoes
Seed	150 – 350
Vegetative Cutting	75 – 150
Vegetative	350 – 600
Reproductive	600++

Species	Cucumbers
Seed	100 – 300
Vegetative Cutting	-
Vegetative	300 – 600
Reproductive	600++

Species	Peppers
Seed	150 – 350
Vegetative Cutting	-
Vegetative	300 – 600
Reproductive	600++

Wattage actually only matters because there is a maximum PPFD range linked to the wattage of an LED system. Wattage is a metric for input, not for output so the wattage doesn't tell you anything about the light (converted electrical power in wattage) that comes out, PPFD does and is your most important metric. For example: a 600 Watts LED light will have a much higher PPFD than a 600 Watts HPS light. So if you would compare these 2 lighting sources based on PPFD, the 600 Watts LED light has the same PPFD as a 800 - 1000 Watts HPS light (considering a high-end LED system).

■ Yes there definitely are! A recent study conducted by the Wageningen University & Research Centre in the Netherlands shows promising results for LED grow lights. They found that the crops that were grown under high light intensity produced a higher bud weight when compared to the same crops grown under normal light intensity.
■ Furthermore, the study found that in all varieties of light, crops grown using LED produced a higher content of active substances than crops using HPS lamps with the same light intensity.
■ The aroma, flavor, and color of a plant depend on the type, strength, and quantity of Terpenes within that particular plant. A high Blue ratio during the last 3 days of flowering ensures an explosive increase in A high Blue ratio during the last 3 days of flowering ensures an explosive increase in terpenes in spices and herbs (this is called the ''Blue Light Treatment'').