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Numerous measures of light intensity in the LED industry has led to consumer confusion. Choosing the right LED grow light can be complicated, especially with all the scientific calculations and data that lighting companies are using to market their products. Consumers struggle with complex math and lighting measurements which are very different from traditional growing technologies and calculations. The average consumer is neither a botanist nor a lighting engineer, so understanding the different spectrums, units of measure, and the correct instruments to read them is difficult. Additionally, the horticulture/agriculture industry has expanded from the traditional two (2) light spectrums to over twenty. Traditional proven spectrums are no longer the norm for LED grow light companies.

Traditional Metal Halide and High Pressure Sodium bulbs in the market:

This raises the questions of what spectrum will result in a successful harvest and which spectrum is right for what species of plants?

Proven Past

( refer to traditional MH & HPS chart )
Traditional bulb manufacturers used a spectrum graph along with Lumens, LUX and PAR values when marketing their products. Today, LED grow light companies use complex units of measure such as Umol per second, YPF, PPFD/w, and Umols per joule. These spectrums are very different than that of traditional proven lamps, creating confusion with the average consumer.

Quality vs. Quantity

LED grow light selection has become as important as the quantity of lights purchased. Grow operations have witnessed capital expenditure in LED quantity instead of light quality, resulting in lower productivity. This consumer perception of LED failure has resulted in many grow operating reverting back to traditional HPS lighting. Furthermore, the lack of LED industry technical standards has contributed to this uncertainty in light selection and its correlation to yield.

Shining Some Light On LED Confusion

Modern grow operations use either metal halide (MH) or high pressure sodium (HPS) bulbs, which can include double ended (DE) lamps. These light sources have historically proven technology and spectrums, and hence have remained the number one choice for grow operations worldwide. Growers tend to use bluer spectrum MH lamps for leafy green vegetation, and warmer tone HPS lamps for flowering plants and food production (reference image # 1).
Bulb companies tend to advertise the spectral output, total lumen output, and radiant flux of their lamps on their packaging. This visual spectrum, typically between 400-700nm, is the same range as photosynthetically active radiation (PAR) which is used to measure the photon energy absorbed by plants. Both measurements use different calibration methods and both are typically on product labels these days.
However, the LED grow light industry has been marketing different units of measurement, namely PAR, Umols/second, Umols per joule and PPFD/watt. As a result, units of measurement such as Lumens and LUX are being phased out.
Did you know that foot candles, Lux , lumens and PAR all measure the same spectral range of 400-700nm which is visible light!!

The Issue With PAR And Umols Per Second Per Watt

The concern with using the units of measurement such as PAR and Umols per second is that because colored LEDs have on the results your meter will display. Colored LEDs play a huge role in how data from one LED grow light company to another may be perceived versus reality and the actual plant growth results.
The most popular current unit of measure for LED grow lights is Umols per second. Using some data provided by CREE LED you can see on the chart (PPF vs Nanometers) how 630 nanometers versus 660 nanometer for example influences the PPF which effects the Umols per second result your meter will display using the same amount of power.

This is important because 630 nanometers (nm) will give off more usable light (Lumens and intensity) than 660 nm. 630 nm is a bright red and 660 nm is a darker, deeper red. Quick logic is brighter color brighter light…

Due to the 660nm peak being closer to the peak of chlorophyll A absorption in that range it will have a higher PAR density effect thus resulting in higher Umols per second when doing the calculations.

Taking this a bit further. Below you can see two images and a chart displaying LED arrays with Umols per second results. The LED arrays both have the same number of white LEDs with the same bin number. Both arrays have 24 colored LED’s. Board 1 has various colors including four 660 nm LED that amount to 16.67% of the 24 colored LED’s. Board 2 has all 24 colored LED’s at 660 nm. The result is a change of only 20 LED diodes.

Looking at the results you can see how the changes effect the result of umols per second by changing only 20 LEDs on an array of 196 LEDs. Some LED grow lights today feature over 500 even 1000 mid power LEDs and thus can reflect very high umols per second readings by having more 660nm LEDs in their arrays than necessary. In fact most companies are over saturating these ranges for higher PAR readings and thus be perceived as a better light source when in fact it is not a clear representation of a fixtures capability.

Studies have found that too much red in this range can cause a stretching effect and when too close to the plants a bleaching effect.

Umols per second is a calculation of total watts used by total PPF. If a fixture has a 2.0 umols per second specification advertised, it by no means represent whether or not that fixture can cover adequate space and or replace a 1,000-1,150 watt lamp. Furthermore since Umols per second is an electrical calculation and can vary based on the electrical efficiency from grow to grow.

A grow light’s total wattage changes based on input voltage. Example using our SK602:
600 watt grow light at 120 volts uses 645watts (from the wall) divided by 1350PPF = 2.09 umols /s/w
600 watt grow light at 277 volts uses 609 watts (from the wall) divided by 1350PPF = 2.21 umols /s/w

The higher your electrical input voltage is the greater the efficiency will be on your LED drivers and thus result in a higher umols per second; another reason not to base a decision of a grow light based purely on umols per second or PAR.
Furthermore, it is also important to look outside the visible spectrum into broader wavelengths such as 300-800 nm because plants use spectrums outside of 400-700nm.


An LED grow light company that advertises and uses a lot of 660nm (deep red) wavelength is sure to have great marketing data showing the high PPF/w of their lamp, but this by no means guarantees success.

Going back and looking at the proven light spectrum of an HPS light you can see that there is not much 660nm present relative to the rest of the lamps spectral output. There are LED grow light companies who insist on spectral outputs that don’t have, at a minimum, what the proven HPS lamps have , but instead do have the opposite of the HPS lamp and expect large grow operations to adopt their new unproven spectrums or so called “science”.

How To Convert From HPS to LED

1. Observe what has worked and been proven and see how the new technology incorporates the old one. If you don’t get a sense that there are any similarities, you run the risk of being another unhappy LED grow light consumer who did not harvest successfully or comparable to the MH /HPS technologies.
a. Using older methods of measurements from traditional proven commercial lighting practices such as LUX, Radiant Flux and Foot Candles (FC) is sure to give a grower success should he or she find an LED grow lamp reflecting equivalent numbers to the HPS they are looking to replace.
b. Even today most gardening stores carry LUX and Foot Candle meters for growers to measure their HPS bulbs to make sure they are still outputting the minimal intensity necessary for a good grow. Use them!!
2. Just because the technology of light sources has changed (incandescent, fluorescent, induction, plasma, high intensity discharge, LED, etc...) doesn’t necessarily mean the measurement of it does. There are many studies which have proven that intensity is more important than spectral quality. Look at the HPS spectrum which may not be so desirable according to many LED manufacturers yet it is undisputed that it works. The sheer intensity of HPS is what makes it so successful and intensity is commonly measured using LUX/FC readings. Even today most hydroponic stores still sale basic LUX/FC meters and barely carry PAR meters.

Looking at Spectrum King LED grow lights (currently patent pending)

You can see how the spectrum compares to proven technologies on the market today. All the spectrums and intensities of the traditional light source are present along with a broader range of wavelengths. It’s these high intensity types of spectral output lamps that are sure to give growers success.
It is recommended that when researching LED grow lights that the end consumer take a step back and look at how the new LED grow lamps compare to what is known to work and then considering all aspects when it comes to units of measure such as lumens, lux and even foot-candles not just PAR or Umols per second. When you see a light that scores highly across all units of measure you are looking at a winner.