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What is the difference between LUMENS and LUX?

The question "What is the difference between LUMENS and LUX" is a common question among new greenhouse gardeners, home growers and even some seasoned growers with years of experience.   The topic itself can be somewhat confusing, so we will do our best to explain it to you so you understand and can relate to what LUMENS and LUX are all about.  We hope you can learn from this information and hopefully pass it along to your fellow growers so they have an understanding what also the difference between them.


LUMENS

What is a LUMEN?  a lumen is a simply a unit of light measurement that's otherwise known as luminous flux.  If we had a source of emitting light, we would use LUMENS to compare the total amount of light output.  However, please understand that LUMENS is not the final calculation of light output or otherwise, in fact, lumens will only tell you a part of the whole story.  When it comes to being capable of producing a superior light beam pattern, it simply doesn't give us enough infromation and details to let us know how the light is actually being used.   If we were to find a suitable comparison, we would suggest it relates to automobile total brake horsepower (bph).

If we wanted to measure LUMENS accurately, we would certainly require an expensive piece of test equipment that would be a specialized light integrating sphere.

Explanation of LUMEN and LUX - DEVICE TO TEST LUMENS

The above picture is a system to facilitate accurate spectroradiometric, photometric and colorimetric characterization. These application-specific systems will accurately evaluate lamp efficiency for flashlight development and manufacture in commercial, marine, military, head-wear, or test even garden lights!


LUX

What is a LUX? Simply speaking LUX is a unit of light measurement taking area into account. In other words LIGHT INTENSITY.

We us LUX to measure the amount of light output in a gievn area, where one lux is equal to one lumen per square meter.   LUX is a superior measurement for us to determin what we see as the brightness of a beam.  For instance if the light output was concentrated over a smaller srea we would see this a super bright.   If the same light output was spread over a much larger area, our eyes would see this as very weak.   

In our everyday normal life, we generally use mirrors, reflectors and other light optics to control or direct the path of the light and therefor create a desired light beam pattern.   LUX also will determin the magnitude of light intensity travelling over distances.   Heres an example, if a light was configured for a high lux, the output would travel farther but will still have a smaller footprint of light (ie: a light in a lighthouse) and if we use a low lux, the level will be configured to travel much shorter distances but have a much larger footprint (ie: ambient lighting or a decor down hanging light).

For us to measure LUX at a specific location, we use a device that ranges in various price ranges.  We recommend buying a good lux tester (or lux meter) if you require a very accurate measurement.  Labratory grade lux meters are the best, but they can get expensive.   If you are a serious gardener, you must get a good one for the most accurate test results:

SPER Lab grade LUX METER for measuring LIGHT OUTPUT

Beam Angle (FWHM)

What is a Beam Angle?  A beam angle is the angle of which a light is emitted. To be more specific, it is the Full Width at Half Maximum.

Since we do not really have any way to accurately measure the 'edge' of light we measure the beam angle from where the light is at 50% intensity (FWHM). By being able to measure where 50% light intensity ends, it gives us the majority of where the light is used thus representing the beam angle. With all smaller beam angles they will have an intense hot spot, where as larger beam angles will have a lesser intensity (due to a larger area).

Check out the beam shot below and see if you can gauge where 50% intensity ends, giving you the beam angle.

BEAM ANGLE - How do we measure beam angles?

Watts

What is a WATT?  Basically a watt is a unit of power that is consumed.

The more power any light emitter consumes, the more lumens it should produce. However, the relationship is non-linear and we can use the numbers from wattage and lumens to measure the efficiency of a light emitter.

The LEDs that are available today have far outpaced the industry as the most efficient light emitter and can produce more light than older halogen lights. One thing to note is the more power is consumed, the more heat is produced, which is wasted energy.