LED Grow Light FAQ
1. Why Buy LED Grow Lights?
The main advantages of LED plant lights are:
- lower operating cost (electricity, replacement bulbs, etc)
- much longer bulb life
- energy efficient
- more control over light spectra
- simple to install
- no need for additional equipment (ballasts, reflectors, cooling equipment)
- environmentally friendly (no mercury)
- increased growth, density and resin output (if used correctly)
The main disadvantages are:
- higher initial cost
- may require additional heating in cold climates
- many low-quality lights on the market (but not on this site!)
- bit of a learning curve if switching from traditional lighting
2. Why do some LED lights have two different wattages?
You may have noticed that some of the LED light fixtures we sell have two listed wattages. This is because some manufacturers advertise their lights using the full theoretical wattage (which is a bit disingenuous, if you ask us).
This is simply the listed wattage of the LED diode multiplied by the number of diodes in the fixture. For example, a fixture with 80 x 3w diodes will have a theoretical wattage of 240 watts. But this fixture will not actual run at 240 watts.
In order to ensure longevity, LED diodes are never run at their full capacity. Instead they are run at around 60% of full capacity (the percentage varies among diodes). This actual wattage is what you want to take into account when selecting a light.
All the lights on Grow Light Central are sorted by their actual wattage, even if the manufacturer uses the theoretical wattage in their product titles (we retained the product titles the manufacturer's use, but make sure to always list the actual wattage in the descriptions and the specs).
3. How do I choose the right light (brand, wattage, etc.)?
When buying horticultural LED lights, you have a lot of options (too many, in fact). On this page, we'll look at three factors that will help determine which light is best for you. By the time you get to the bottom, you will have a good idea of what you need.
NOTE: We also have a much more in-depth LED buying guide specifically for marijuana growers. Check it out here.
The three factors to consider are:
1. Type of Plant
For our purposes, there are basically two types of plants: those requiring a lot of light and those requiring less light. Plants with high light requirements include cannabis, tomatoes, etc. Plants with low light requirements include herbs and leafy vegetables.
Most visitors to this site grow cannabis (remember to adhere to local laws!), which means they need more powerful lights than someone with an herb garden.
The best lights for growing cannabis come from brands that specialize in marijuana and whose lights have proven to effectively grow it from clone to harvest by real-world growers.
Optic LED lights are also excellent and quite a bit cheaper than the other brands. The reason for this is that they are manufactured in China, but they're an American company, so you still get American quality control and an American warranty (5 years).
Note: If you are growing plants with lower light requirements, I recommend the same brands. The difference will come in the next step, when we figure out your wattage needs (hint: you'll need less and will save money).
2. Number of Plants and Size of Grow Space
For our wattage calculation, we are going to use the actual wattage (as opposed to the average wattage—you can find an explanation of the difference in question 2 above).
For Plants With a High Light Requirement (cannabis, tomato, etc.)
The basic formula is: 25 actual watts per square foot of grow space.
Thus, a grow space that is:
- 2' x 2' (4 sq. ft.) will need 100 watts of LED power
- 3' x 3' (9 sq. ft.) will need 225 watts
- 4' x 4' (16 sq. ft.) will need 400 watts
- 5' x 5' (25 sq. ft.) will need 625 watts
- 6' x 6' (36 sq. ft.) will need 900 watts
For Plants With a Low Light Requirement (herbs, leafy greens, etc.)
The basic formula is: 16 actual watts per square foot of grow space.
Thus, a grow space that is:
- 2' x 2' (4 sq. ft.) will need 64 watts of LED power
- 3' x 3' (9 sq. ft.) will need 144 watts
- 4' x 4' (16 sq. ft.) will need 256 watts
- 5' x 5' (25 sq. ft.) will need 400 watts
- 6' x 6' (36 sq. ft.) will need 576 watts
Number of Plants
The number of plants actually has no bearing on this calculation, but if you are trying to figure out how much wattage you need for a certain number of plants, you can make use of the same formula.
First you need to estimate how many square feet your plants take up. Since most of our visitors are cannabis growers, we'll use that as an example.
A smallish cannabis plant takes up about 1 square foot. In this case the calculation is simple: since we need 25 watts per square foot and one square foot equals one plant, we need 25 watts per plant. Thus ten plants would require 250 watts.
A larger plant might take up two square feet, in which case each plant would need 50 watts (25w per sq.ft. X 2 sq.ft. per plant = 50w per plant). Ten such plants would require 500 watts.
If you are using low-light plants, simply perform the same calculations using the 16w per sq.ft. figure.
If you need any help figuring out your wattage requirements, please feel free to contact us at firstname.lastname@example.org.
We always answer within a few hours at the most and will be more than happy to help you with these calculations.
3. Growth Stage
The final factor to consider is for which stage of plant growth you will be using the light. If you plan to use it for the vegging stage only, you would be best off getting a light with a mostly blue spectrum, specialized for that growth phase.
Similarly, a mostly red spectrum light will be best for the flowering stage.
Most growers prefer a light that can take their plants all the way from clone to harvest. For this you'll want a light that includes both the red and the blue spectrum.
We prefer to use full-spectrum lights (see question 4 below for an explanation why), but there are different ways manufacturers achieve a full spectrum light with LEDs: white diodes or multiple colored diodes. There is no conclusive evidence that proves one is better than the other; it's just a matter of preference.
Many growers prefer to use full-spectrum white light, which most closely mimics natural sunlight.
Advatages of white LED light:
- most closely mimics natural sunlight
- makes it easy to monitor your plants' health (if you are using reddish or blueish lights, you have to get them under natural light to really be able to see how they are doing).
Disadvantages of white LED light:
- generally a little more expensive
- includes light in spectra that are not absorbed by plants (like green), meaning it goes to waste
If you are interested in using white LED light, the NextLight line of lights is your best choice. These lights use less power and run cooler than even other LED lights. They're pretty amazing, but they're not cheap.
Colored LED Lights
Most manufacturers use a combination of diodes in different bandwidths in the red and blue spectra. If the lights use the right bandwidths and the ratio of red to blue light is correct (6:1 or 5:1), these lights are very effective in taking your plants through all stages of growth.
All of the lights on this site are optimized for plant growth. They contain diodes with the appropriate bandwidths and in the correct ratio of red to blue, so you do not need to worry about figuring this out on your own.
Our most popular sellers, the Black Dog LED line of lights, use their proprietary Phyto-Genesis Spectrum™, which contains the perfect mix of colored diodes for every stage of plant growth.
4. Summary and Recommendations
If you want a light that you can use through all stages of plant growth, check out our best-selling full-spectrum lights:
- NextLight for white light
- Black Dog LED for light using multiple red and blue bands
- Optic LED for a mix of white COB LEDs and colored 5 watt chips; also great for those on a budget.
We also have a great post that reviews the 4 best 1000 watt LED grow lights. Check it out if you're considering that wattage.
If you are looking for a light for the only one stage of plant growth (veg or flowering), go with:
- The NextLight Veg8 for the perfect (full-spectrum) vegging light
- Optic 6 3000K for a blooming master
- Advance Spectrum if you are on a budget
Check out the different offerings from those manufacturers and choose a light or a combination of lights that will output enough wattage to cover your grow space (as determined in step 2 above).
If you have any questions about choosing a light, please contact us at email@example.com
We will get back to you within a few hours (and usually much sooner).
4. What's better, separate lights for veg and flower or a full spectrum light?
While plants definitely prefer more blue light during the vegetative stage and more red light during the flowering stage, they don't want only those lights. They still want some of the other color during each phase.
We recommend using lights that provide all the spectra needed throughout the growth cycle in one fixture. Here's why:
1) Eliminates the shock plants get when lighting conditions change
When a plant grows leaves, those leaves are optimized for the light they are grown under. Changing the spectrum shocks the plant, because the existing leaves aren't optimized for the new conditions.
New leaves grown under the new lighting conditions will be optimized for them, but until those new leaves have grown, the plant will not be able to make the best use of the new light you're providing.
Using the same spectrum throughout the plant life eliminates this shock and results in a decrease in flower time of around one to three days. It also results in an increased yield.
For this reason, many growers use both MH and HPS bulbs during all stages, but with LEDs, we can provide all the spectra needed during all phases of growth with a single fixture.
2) Higher quality plants during the flowering stage
Under HPS lights (or other red-heavy lighting), plants grow taller, but develop weak stems. The reason for this is that the upper canopies block out most of the sun's blue light in nature, while the far-red light is able to penetrates to the lower leaves and smaller.
As a result, plants have evolved to encourage rapid stem growth when their light has a low blue-to-red light ratio. Their internodal spacing increases so they can grow tall and stretch through the canopy keeping them from the blue light.
Giving your plants the proper ratio of blue light throughout all stages keeps them from trying to stretch upwards. Their internodal spacing is shorter and the stems stay stronger. The plants also waste less energy trying to grow upward and use that energy to produce flowers or fruits instead.
3) Higher quality, denser flowers
The shorter internodal spacing results in denser flower inflorescence, aka buds.
5. How much money can I save using LED lights?
We performed a quick (and very rough) calculation to estimate the cost savings of LED over HID. According to this calculation, you will recoup your initial cost of purchasing a 500 watt LED in the second year. After three years, you will save over $100 and after five years, you will save over $2500. Here's how we arrived at those numbers:
- We compared a 500 watt (actual wattage) LED light to a 1000 watt HID light. If the LED fixture is of a good quality, these two are about equivalent.
- We used $1500 as the initial cost for the LED light and $500 as the total cost of all the equipment needed for an HID setup (reflector, ballast, bulbs).
- We used a cost of electricity per year of $710 for LED and $1420 for HID ($0.1297 per kw/hr with the lights running every single day of the year, 18 hours a day during veg and 12 hours per day during flowering).
The following table shows the total costs (initial cost of equipment + electricity cost) for years 1 through 5.
|Year||500w LED||1000w HID|
Remember, this is just a very rough estimate and it also doesn't take into account any of the additional benefits of LED lighting (or the drawbacks) or any of the additional costs of running HID lights, like the cost of cooling equipment and the electricity cost to run that equipment.
6. What is the difference between lumen and PAR?
This can get pretty technical, so I'll try to keep is as simple as possible: lumens are for humans, PAR is for plants.
Lumen is a measure used for the amount of light seen by the human eye. Plants do not use the same wavelengths of light that look brightest to us (green and yellow for example). As a result, the lumen is not the most accurate measure when determining the effectiveness of a grow light.
PAR, which stands for Photosynthetic Active Radiation, refers to the area of the spectrum of light where plants and light interact (between 400nm and 700nm). The unit used to measure PAR is the μmol/s (micro mols per second) and it measures the number of photons in the PAR spectral range that fall on the plant each second.
7. How far from the canopy should my lights be?
This actually depends on a number of factors, like the wattage, the brand of light, the beam angle, the coverage area, the shape of the light, etc. Your best bet is to follow the manufacturer's recommendation, but if you want a general range, stick to 24 to 36 inches from the top of the canopy to the light.
8. Why do some of the diodes on my LED panel not light up?
Some LED panels have diodes that do not light up. Don't worry, they're not broken! Those diodes emit light in the ultraviolet and infrared spectra, which are outside the range of visible light (400-700nm). Many manufacturers include them, because they encourage resin production and complete phytochrome response.