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LEDs, Lumes & LUX


New Member
I have been putting some time into researching LED light options. They are not cheap, so I am taking my time. I found this piece that I think distills down some of the terminology and how to compare/contrast output.


LEDs are widely accepted as a low energy light source for illumination of living spaces and many questions have been raised by individuals attempting to understand how much light is produced by a High Brightness (HB) LED when compared to an incandescent light bulb. HB LEDs are characterized by luminous intensity, usually in millicandelas, candela, or Lumen (mcd, cd, lm) in an LED specification, while most incandescent bulbs are rated in watts and lumens. How can you compare them?

Bulb brightness in Lumens

A 100 watt Bulb is rated at approximately 1700 lumens
A 60 watt incandescent bulb is rated at approximately 800 lumens
A 40 watt bulb is rated at approximately 400 lumens
A 25 watt bulb is rated at approximately 180 lumens
A 4 watt night light bulb is rated at approximately 20 lumens

LED ratings of 25,000 mcd become conceptually difficult to understand when we are accustomed to light being expressed in terms of lumens. Published lumens represent the sum of all the light emitted by the bulb in all directions.

Light measurement basics

Both candela and candlepower correspond to the amount of light (i.e. the quantity of photons) produced by a standard light source. Originally, the standard light source was a real candle so it is also called candlepower. But like most measurement standards, it's now a theoretical construct having a specific wavelength of visible light at a specific power level. The good news is that the intensity of the standard candela is nearly identical to the original standard candle. All other quantitative measurements related to light are derived from the candela.

Candelas are a measure of the amount of light generated at a source. Lumens quantify how much total light flows away from the source. Foot-candles and LUX indicate how well the surface area of an object, wall or floor is illuminated at some distance away from the source (intensity of the light reflecting off objects like the floor, wall, or work-surface).

So what does this mean? If you have a light source of 1 candela, it's also 1 candlepower in intensity. If you measured the light on a 1 square foor surface, 1 foot away, it will have 1 foot-candle of illuminance over it's surface. In metric terms, if you measured the amount of light on a square meter that was 1 meter away, it will have 1 LUX of illuminance.So you could say that the light source is generating 1 Lumen in the direction of the 1 square meter that is 1 meter away. If the light source is in the middle of a sphere and generating light in all directions, you will find that the 1 cendella light source is generating 12.57 lumens as explained below.

Light Measurement Equivalents and Common Illumination Levels:

- 1 square meter (M2) = 10.7638 ft2
- 1 LUX is defined as 1 lumen/ M2 of a surface; thus 1 LUX= 0.0929 FC,
- 1 foot candle (FC) is 1 Lumen/ ft2 of a surface; thus 1 FC=10.7638 LUX
- There are 12.57 square meters on the surface of a 1 meter radius sphere.

In real life objects are illuminated and measured in LUX:

- Full Daylight is about 10,000 LUX (imagine 10,000 lumens each and every square meter!)
- Cloudy day is about 1,000 LUX
- A lighted parking lot at night is about 10 LUX (average)
- A full moon is about 0.1 LUX

OSHA Lighting Level Recommendations for Work Spaces:

- Public spaces with dark surroundings.................................30 LUX
- Simple orientation for short temporary visits........................50 LUX
- Working spaces where visual tasks are only occasionally performed...100 LUX
- Performance of visual tasks of high contrast or large scale.........300 LUX
- Performance of visual tasks of medium contrast or small size........500 LUX
- Performance of visual tasks of low contrast or very small size.....1000 LUX

In LED specifications:

- lm is lumens - total luminous flux flowing from the LED. mlm = millilumens.
- cd is candelas - the luminous intensity at a specific forward current. mcd = millicandela.

Cd or mcd units are usually expressed as a value relative to the viewing angle. The larger the viewing angle, the more light flows given the same intensity. In other words, 1000 mcd over 130° viewing angle is a lot brighter (more lumens) than 1000 mcd over 20° viewing angle. Lumens (lm or mlm) usually refers to the total light output of the device at the rated current.

Steradians - Solid Geometry Lessons Anyone?

By definition, 1 lumen is the amount of light produced by a 1 candela source radiating out through 1 steradian (a specific cone shaped solid unit angle of 65.54°) within an imaginary sphere surrounding the light source. One candela illuminates the entire surface of a 1 meter radius sphere at an average 1 lumen for each sq. meter of surface in the 360° sphere. There are 4 π, or 12.57 steradians in a sphere. Thus, the standard candle at 1 candela intensity produces 12.57 lumens of total visible light radiated in all directions. Lumens are the total quanty of light flowing out in all directions.

a steradian An LED specification sheet shows the luminous intensity (mcd) of the LED for a specific viewing angle of the LED. The viewing angle is the angle of the beam of light produced by the LED and lens. The angle is bounded by the edges where the intensity falls to 50% of the max intensity usually found at the optical center of the beam. Thus, a 25,000 mcd LED with a viewing angle of 20° can provide 25 Candelas of light intensity within the 20° viewing angle. The question most often posed is how many lumens do you get from this type of LED light?

We can find this out by understanding the relationship of candelas, steradians and spheres using the diagram below. Note that the sphere segment has a 1 meter radius.

Calculating Candelas and Lumens

A steradian is a solid cone having 1 square meter of surface area on a sphere having a 1 meter radius. There are 4π (12.57) steradians in a sphere. The light grey area is known as a spherical cap that we will illuminate with a point light source.

The surface area of a spherical cap is calculated using the formula S=2πRh where h, the height of the cap, is completely dependent on the viewing angle (apex of the cone). A smaller angle, results in a smaller area on the surface and a smaller height of the center of the cap.

LED Viewing Angle Calculation If you remember your trigonometry, we can calculate the height of the cap h, in a 20° cone (the viewing angle) by finding the length of a 10° right triangle. A 1 Meter radius simplifies the calculation and the height is found using the formula 1-Cos(10°). Notice we use half of the viewing angle for the calculation. LED specs will show either viewing angle or half angle so it is necessary to distinguish between the two when reading the spec. Viewing angle is denoted by "2∅" in most LED specs.

At 1 meter, a 25,000 mcd LED with a 20° viewing angle covers a spherical cap area of 2*π*1*0.015 = 0.095 square meters with 25 candelas of intensity. In order to determine total lumens flowing, we must determine how bright the intensity would be if the same amount of light flow were covering an entire 1 square meter area on the surface of that 1 meter radius sphere. We know that the 20° cone covers 0.095 M2 and multiplying that small area times the candela value tells us how many lumens the device delivers into a 1 M2 area. This half angle cosine formula 2 π*(1-Cos(∅))*25 Candelas yields [6.283*(1-cos(10°))*25] = 2.39 lumens.

Now that we've standardized our light output in lumens per square meter, the same LED die, when used with a wider beam lens (i.e. 40°), will have a lower candela value. Using the above calculation, a 25,000 mcd 20° viewing angle LED has the same luminous flux as a 6,250 mcd 40° viewing angle LED. This is the same LED die with a different lens. Recent LED specs have begun to include lumen values to help in this determination of total light output.

This mathematical method is a close approximation of lumens using the candela value and the viewing angle of the LED. Other factors in the construction of the LED can change the luminous flux relationship with the luminous intensity of the die. For example, some LEDs will have less light lost to the sides and rear of the die and reflect more of the intensity out through the lens.

LED Radiation Diagrams

A radiation diagram for a specific LED shows how the viewing angle is distinguished from all the other light emitted by the LED. The red arrows indicate the 60° half angle or 120° viewing angle where the light drops to 50% of max intensity. This is the forward radiation. Note that the most light is usually on the 0° X axis and this represents the maximum candela output. Note also that as the light spreads out across the viewing angle, the relative candela output drops to zero (in this particular case) at 90°.

Any light that is absorbed into the substrate of the LED base is not seen or measured. You can see why altering the construction of the LED to reduce light lost in other directions would cause a change in the lumen output.

When an LED spec sheet specifies the lumen output rather than candela or millicandela, the Total Luminous Flux (lm) number represents all the light that is emitted from the device as measured by an integration sphere. The radiation diagram is used to see what the relative level of light is as it radiates out in any given direction.

Comparing real bulbs to LEDs

Let's compare a standard 4-watt night light bulb with a high brightness white LED. The night light bulb is rated at about 20 total lumens. The difference between an LED light source and a free standing bulb is that the 20 lumens are radiated out in a 360° 3D space. We would need 10 LEDs rated at 2 lumens each to obtain the equivalent total luminous flux. An object in the room will receive only a portion of this flux. When the 4-watt, 20 lumen bulb is placed in the center of a 1 meter radius 360° sphere, the surface area receives 20 / 12.57 = 1.6 lumens per M2. At 1 meter, that is 1.6 lux.

An LED having a 20° viewing angle illuminates 0.095 M2 at a distance of 1 meter. The LED is required to have a luminous intensity of 1.6 lumens / 0.095 or 16.8 candelas to deliver 1.6 lumens over the entire square meter to equal the 4-watt bulb's light output. With luminous intensities ranging from 20 up to 40 candela, today's hi brightness LEDs can easily produce this light output.

When a night light is plugged into a wall receptacle, typically half is directed into the room while the other half is reflected off the wall. Any reflection off the wall increases this with indirect lighting. A mirror would reflect nearly all of the light while a painted wall could reflect less than half depending on the color and surface finish. Absorption in the plastic decorative shade also reduces the total lumens of direct light delivered to the room.

Comparing LED Watts and Incandescant Lamp Watts

There seems to be a lot of confusion over this as many people want to compare LED watts with incandescant watts. The short answer is that they are not easily comparable! An incandescant light bulb consumes 40, 60 or 100 watts of POWER. Approximately 90% of power consumed is given off as heat and the rest given off as light. The term Luminous Efficacy is used to describe the ratio of the visible light energy emitted to the total power input to the lamp. This visible light is measured in lumens.

Incandescant lamps are full spectrum devices where LEDs are not. LED's will give off a specific range of wavelengths. The power consumed to do this is very little compared to incandescant lamps.

As an example, assume a 350 mA LED with a forward voltage drop of 3.2 Volts. Using Ohm's Law, (Power = current * voltage or P=IE)you can see that this LED will consume about 1.12 Watts. CREE has XLamp XR-E LEDs that can produce over 200 Lumens at this power. Comparing that to a 25 watt incandescant lamp (approximately 180 lumens) becomes difficult because the lamp consumes 25 times the power of the Cree LED but the LED has more visible light output. One must also consider the inefficiencies of converting AC to DC power, but even a 70% efficiency demonstrates that the LED is far superior to incandescant bulbs for illumination efficiency.
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New Member
but even a 70% efficiency demonstrates that the LED is far superior to incandescant bulbs for illumination efficiency.
I'm a newbie with a green thumb and a fair amount of LED/ Electrical experiences..I've built, repaired and installed the LED lighting for industry for a number of years. I dont know a great deal about the math and stuff, like that, I just see the specs, load demand and the results after the install.
Great article with a lot of actual physics backing what he is laying down, but, now how would LED compare to HID in terms of ability to supply light to the showgirls? The presumption is that LED would of course be better (for the power bills of course), but what does the physics say of the matter regarding light output, spectrum analysis, comparable to HID and especially in terms of simple real world growth and the amount of pounds of bud I can put in the jar? In my future grow op, I'm going to NEED the heat the lights produce to maintain growing temperatures in the outbuilding so this is a major consideration.

Great post, thank you!


New Member
I am heavily investigating LED options. Sylvania's Zelion HL 3x2 and Spyders MCOB 9x. have my interest so far... Thank you for this illuminating lesson. I have full faith that little is known about the potential in LED growth panels. Please msg me if you have insight to the future of this tech. MCOBs seem to be the future. I want to make a wise purchase with electricity reduction as a driver. Thanks!


New Member
Hey, Erinmore.

I'm a new member. with an interest in going led because I want to reduce the heat signature. Nasa has a very interesting article on LED gardening. The summary was that much needs to be studied in what we refer to as PAR. Many of the wavelengths pushed by HPS aren't efficiently used by the plant. So a simple PAR test overstates usable light. A heater would be a much more efficient means to heat that outbuilding. Im an Electrician also. Sadly, not retired yet though! ...what is MCL? I am so happy to be here among so many friends to the cannabis plant!!! Have a wonderful day!


New Member
Im sorry but my inglish is not that well as all of you here but if i was bould a combo mis of all lights what would you advise me to get for a 10 square meter grow room and mony is no object for the matter tell me what to combine inorder to get good yield and quality bud thank you in advance


Well-Known Member
hey guys i have a very simple question i am in the process of growing and wanted to use a lux meter to measure the light in my room but im using led lights will i still be able to get a realistic reading from them?


New Member
hey guys i have a very simple question i am in the process of growing and wanted to use a lux meter to measure the light in my room but im using led lights will i still be able to get a realistic reading from them?
That is a good question. I never even thought that there would even be a difference, yet it makes sense with the different wave lengths. See if we can get some answers.Thanks.


Well-Known Member
Hey, Erinmore.

I'm a new member. with an interest in going led because I want to reduce the heat signature. Nasa has a very interesting article on LED gardening. The summary was that much needs to be studied in what we refer to as PAR. Many of the wavelengths pushed by HPS aren't efficiently used by the plant. So a simple PAR test overstates usable light. A heater would be a much more efficient means to heat that outbuilding. Im an Electrician also. Sadly, not retired yet though! ...what is MCL? I am so happy to be here among so many friends to the cannabis plant!!! Have a wonderful day!
Say I really need an electrician to help set my lights etc... I'm in Tauranga New Zealand.


New Member
Beautiful country, New Zealand. Did you have a specific concern? What do you need help with?

"Hoping to spread the Good Word of Cannabis...
- Johmby
Right on time. I really want to get box my hps/mh because my tents are not set up in a garage, but inside, and the heat is so overwhelming. I'm using up my remaining CFL's and I'm buying two LED's in the next ten days, because it seems like the light distribution/penetration is more favorable when using more than one, or am I confusing something?


Well-Known Member
Checked out the thread, peaked around your site.... Didn't really see much info as to "what" it is you make/sell, and having to fill out a form just to get more info is kind of blah...... No pricing or anything.....

My best guess is Plasma lighting, seems interesting, haven't read a whole lot on it though.


New Member
guys hello from greece!!!Led is what everybody talking about and some things are valid and some not..A very very good and full spectrum led panel is made in greece,ASTIR asl30 (100 euros for 30w)but with very good results and tested by a lot of people in greece,if u are looking for leds these guys are the best!!In yours place which led company do you have to tell me to check?I am a small grower i grow autos,1 or 2 each time..i have a question guys,by your opinion how much watts from led bulbs do we need for a single auto?My growtent is 40x40x1,60(centimeters)..Thanks and keep up the good work,you can learn a lot in here,thats my first post so lets go boys and girls ;-)


New Member
Hi Johmby
I have used HID , CFL and LED . I grew 2 iced grapefruit under 2 125w CFL's (veg) 2 125w CFL's (flower) and a 400w HID all together , the results where staggering, I vegged 18/6 until they where about 800mm from pot base to tip then pinched them out, when the 2 top branches started to stretch I then put them on 12/12 and let them flower, when the buds where showing good strength I trimmed all of the satellite leaves and carried on, I cropped at around 10 weeks ( I don't really go on directed time scales, I tend to follow what the plant dictates) I took 9 ounce dry from each plant.
I grew in coco repotting in three stages to avoid root Knotting and finished in 12" pots.
In veg I fed Canna coco A&B as per directed on the bottle which achieved 1100ppm.
In Bloom I fed the same plus Green planet Massive (the stuff that smells like caramel) as instructed on the bottle which achieved 1450ppm.
I kept temp at around 23c to 25c , humidity at 45 to 55 %. PH was 6.1.
I did the same under 2 600w morsen LED's and achieved half the result.
the conclusion I came to is that you will only get out from what you put in in watts. my first was 900watt using 900watts real time , my second was 1200 watts (apparently according to morsen) using 420watts real time .
so the yield represented the input.
Hope this helps your decision making and sorry for the epic reply but I guess you are looking for evidence of actual grows.
good luck


New Member
Hey , i need help from a professional or someone with knowhow pls-- i will start to grow and i got a speace from 60x60x145 cm or 80x80x80 cm--

i wanna do it as good as i can- so for my space, what is the right led lamp? Does a 12 band full spectrum mean that uv light is involved? or just ir light? what is right?

my first choice was viperspectra 450 w but i ask them on amazon and they said they got no uv light in it-- plus its not that good for blooming

than i wanna go with mars hydro 2 400 w- but it also dont got uv light as far i know till now- is this right that mars hydro 2 got no uv light?--

and we`re almost in 2018 now-- are there studies now that uv does provide more thc or is generally better for indoor and the plants?
so if jes my next step would be a Advanced Platinum Series P300 or 450 w- this got uv for sure-

so what sould i do now if i wanna have good resulst ?? Is there now a noticeable diffrence to no uv or uv light =?

i mean if there is no diffrence with uv or not i should take the mars hydro 2 or my space or the platinum led with uv light?

and is the 300 w platinum led better than a 400 w mars hydro 2 for my max.4 plants or should i take the 450 w platinum led then?
could a platinum led 300 w handel 4 plants max? or like the mars hydro 300 w (withe one )just 2 ?

and if uv is not that important i would go with mars 2 i think-- or is platinum led 300 w or 450 w for liek 200 euros more than my mars hydro 2 in the end so much better and i should invest this ``little ``bit more money for the 300 or 450 w?

and did someone grow with the new niello led grow lmps with any w? they claim to be as good as the others cheeps like mars and viperspac but got uv light and stuff!?

last thing-if i go with mars hydro 2 400 w for my tent - sould i take 2 of mars hydro 300 w(white model) or is one 450 w better?
thx for all good helps


New Member
i was wondering if-someone could help me choose between the better of these 2 LED light bulbs for my grow box (and no lol my grow box isn't finished)


Well-Known Member
Hi Ownplanet,

If you want the best lights to grow you need to look for broad spectrum lights. This means the entire spectrum, not just blue and red (Burple) spectrums. But also the white/green in the middle. Most LED Grow lights don't have white (which really is a blue light to the plants, but looks white to humans). The way many manufacturers work it is like this, blue spectrum is on the left side of the spectrograph (420nm) red spectrum is on the right side of the spectrograph (720nm). This means the graph has 2 peaks, one at 420nm and another at 720nm, they call this "full spectrum" because it goes from one extreme to the other extreme, but those are completely dead in the middle between the blue and red. This is total BS! Lights will hugely benefit from more than just blue and red, they need green. Proven by a plant scientist named Bruce Bugsby. One of the smart guys who worked on the early sustaining life space program.

A very good write up about led grow lights and the technology behind them is here LED grow lights Archives | LED Habitats

The other issue is the wattage claims. Mars Hydro is one of the bad ones, they claim 400W, but in reality it really is only using 162W. And this 162W is putting out a very poor grow light spectrum (Burple). With low par (Umol) values.
There are only a few broad or full spectrum lights out there, ones that have green LED's in them. There are even fewer that publish real and honest performance numbers. Even fewer that don't exaggerate the results!

LED lights are often compared to the HPS wattage equivalents, this is totally bogus. It is not about wattage, it's about micromoles (Umol). Umol is the photosynthetic spectrum of light, Humans cannot see this. But plants can and use it for photosynthesis. The other issue about using watts and HPS comparisons is that HPS lamps waste up to and more than 60% of the wattage in heat output.

Quality LED's grow lights also don't use cooling fans.

To the OP: it's not at all about lumens. Lumens are for Humans! It's what we can see and perceive as light brightness. Plant growth is about Umol. Typically plants need a minimum of 180 Umol to be happy and a maximum of around 800 Umol. Above that there is a risk of burning the plants (sunburn). It's also about DLI (Daily light integral) this is how many umol's plants receive during a photo period. With weed in flower it would mean in a 12 hour period. Most plants are happy between 5DLI and 35DLI with pot being on the higher end. Typically with pot a DLI of 18-25 is about right. If you get above that the plants start spending more energy trying to shed the extra light they receive than they spend in photosynthesis, very counterproductive. Our sun emits as much as 60 DLI at high elevation bright sky. This is why often times the plants do much better in the shade or partial shade. Some of these super high output grow lights, LED's and HPS put out an astonishing 95+DLI.

Ask if you'd like to know more details.

Happy Growing,
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