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Lumens vs. Kelvin


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#1
ProFlatlander15

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what is the difference between Lumens and Kelvin ratings?

#2
FAC_WNY

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Lumens is the STRENGTH or INTENSITY of the light source, the Kelvin rating is the bulb temperature, or the colour that the bulb appears to be. (The higher the K rating, the bluer the bulb)

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#3
jthyge

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As far as i know...

Lumen i the amount of light.

Kelvin is the color of the light..
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#4
bravoreefer

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I blelieve Lumens in the amount of light output and Kelvin, I know, is what temperature the sun is when it omits that kind of light.
Example: Where ever the Sun is 10,000K hot, that omits the white light as a 10000K bulb would.

#5
Cellenzweig

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Originally posted by bravoreefer
I blelieve Lumens in the amount of light output and Kelvin, I know, is what temperature the sun is when it omits that kind of light.  
Example:  Where ever the Sun is 10,000K hot, that omits the white light as a 10000K bulb would.



You're correct about the lumens, but not the color temperature. The sun is far hotter than 10000 degrees kelvin. (The Corona, or outermost layer of the sun is well over 2,000,000 degrees K and the core is over 15 million) Color temperature is determined by heating a carbon block. If you heat it to 500-1000 degrees Kelvin, the carbon will glow orange. This is about the color of the light a candle would produce. As you get up into the 2000 - 5000k range, the glow is much more yellow. As you approach 10k, the carbon is glowing white-hot... about the colour of a 10000k bulb.

I believe "degrees kelvin" are the same as "degrees celcius", except the scale starts at absolute zero.

#6
ProFlatlander15

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at home depot or lowes the bulbs there do not have a color temperature, they just have lumens on the package. could you get a high lumen bulb and still have a low kelvin rating? like 800lumens, but only 5000K or 300 lumens and 10000K? or does that not work?

#7
Cellenzweig

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Generally, when it comes to light bulbs, High lumens = lower color temperature. E.g., a 400w 6500k MH puts out more lumens than a 400w 10000k (which puts out more lumens than a 20000k).

However, it is impossible to determine color temp from lumens. It all depends on the properties of the bulb. Most "curly" type compact-flourescents and incandescent bulbs fall well below 4000k. Only a few of the "cool white" bulbs are closer to 5000k. They are great for a fuge, but need lots of actinic supplementation on a display tank - and may produce algae problems as well.

#8
GedemeisterDK

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0 kelvin = -273 celsius aka absolute zero (but same scale).

#9
FAC_WNY

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Isn't it -276C?


Damn that science..lol

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Fred
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#10
GedemeisterDK

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;)

#11
ProFlatlander15

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lol i kno what kelvin temperature is for warm/cold...lol i was talking about the kelvin rating of lights..like 10000K, 6500K, etc... its all good tho

#12
apophis924

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The K ratings you refer to are actually based on the THEORETICAL BLACK BODY, not a carbon block. The black body in theory is not affected by ambeit temps or has any heat loss, In other words ALL the eat you put into it is emitted back as EM radiation. Of course this is impossible for real objects. But the black body temps are close enough for laymens use so that the variation in color temp of a black body and the actual color temp of "real lighting" are insignificant which boils dopwn to you heat a black body to 10,000K the color it glows would be very close to the standard 10k bulb when illiuminated. The reading is more accurate for your halides and incandesnt lamps, Flouresence lamps come close but their color is also a function of phosphor coating and they type of gas excilted. Still the numbers are close enough for laymens use.

#13
Kai One

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There is no strict relationship between Lumen, PAR, and Kelvin (maybe Lumen and PAR I don't know), Kelvin refers to the blackbody temperature of an object necessary to produce a specific combination or wavelength in light. That is, as an objects surface is hotter it radiates higher wavelengths of light (i.e. ROYGBIV is low K to higher K). A bulb that has high lumen puts out lots of light, but the phosphor that coats the bulb is specifically designed to emit a certain spectrum. If you buy a high lumen bulb you will get a bright bulb, but not necessarily a white or blue bulb. 6700k is referred to as daylight as it is most accurately reproduces the spectrum of light in the sun. The higher the K rating the more blue/purple (or "cool..." ironic no?) a bulb is. The lower the K the more Red (in most cases yellow) a bulb is or "warm." Most often, the brighter a light is, the lower its K rating at the same type of light or wattage (at least that is what I understand). For example a 6700K MH will have more PAR than a 14000K MH of the same wattage. I am not sure why this is, I think that the phosphorus required probably blocks some of the light, or the energy is consumed by the process of making the light into that spectra (something relating to what is said above about black bodies and energy consumption). 6700K is said to give more growth (due to more light) than a higher K rating, but a higher K rating has more of the blue "actinic" effect, supposedly recreating the spectra blocking effects of water (ie the higher wavelengths penetrate better, i.e. corals need more high spectrum light).

#14
uglybuckling

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Originally posted by Cellenzweig
Generally, when it comes to light bulbs, High lumens = lower color temperature.  E.g., a 400w 6500k MH puts out more lumens than a 400w 10000k (which puts out more lumens than a 20000k).  



This is somewhat misleading inasmuch as it suggests a link between lumen output and color spectrum. Though it is true that it is easier to produce higher lumen output at lower kelvin ratings, it's important to realize that the two things (kelvin color temp and lumens) have NOTHING to do with one another. The only reason low kelvin bulbs (4000-6500K) tend to have higher lumen ratings is because it's easy to produce high-output bulbs with such low kelvin temps. By-product of manufacturing and physics, not the result of a direct relationship between color temp and output.

Corals do not *need* more high-spectrum light...they actually (as you said) grow better under low-spectrum (6500K) light, because more of this light is useable by the symbiotic algae that they harness for energy. Thus the PAR of low-kelvin bulbs is higher, and most growers use 6500K bulbs or 10000K bulbs over their prop tanks. Corals look ugly under these bulbs, but grow very fast. Given more blue (20000K or higher) they fluoresce more and look better. Hence 20,000K bulbs and to some extent 14,000K bulbs are a tradeoff between looking good and growing fast.

Obviously there are some corals that can use blue light better than others....those that live at lower depths (and naturally get more blue light) will probably do better under lights that have more blue in them. There are natural pigments that absorb blue light (cryptochromes are one example, but I don't know how energetically useful these are)....anyway, blue light isn't *unusable* for corals, it's just not as good for most of 'em as yellower light.

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