# NM ratings for red spectrum?



## CatG (Apr 10, 2010)

In my desperate attempt to understand what light I need (and why), I keep getting stumped by the NM ratings on "daylight" bulbs. The reading I have done seems to indicate that plants need red spectrum lighting around the 670 NM range. I keep hearing that 6400-6500k "daylight" bulbs are good for growing plants, but they usually seem to have red NM ratings in the high 500s to low 600s (more orange). Is 670 NM an incorrect rating for plants? Is it better to have the NM ratings in the low 600s? I am having a hard time finding flourescent bulbs with a high 600s NM rating, but have found some red LEDs with ratings that high. However, the red LEDs are really red, and would cast a red light, which I don't really want. If I do actually need a high 600s NM rating, will the redness of the LED light be blended out if I used other whiter lights?

Also, as a side note, a rep from Cree sent me this graph of their white LED lights. In the email, he told me that the "warm white" LED (pictured on the graph as the red line) had the red spike at 660 NM. To me, it looks like the red spikes at about 620 NM. Am I reading the graph wrong?

Thanks,
Cat

Ps. Not sure if the image hosting will work. If it doesn't, I will try to fix it.

EDIT: Can't get the pic to work, but it can be copied and pasted.
www.freeimagehosting.net/2f355


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## Zapins (Jul 28, 2004)

I think you may be becoming too concerned about getting the exact numbers that plants theoretically need to grow instead of buying lights that will grow plants and look good to your eye. Plants are highly adaptable and will adapt to nearly any color bulb as long as there is enough light being emitted. In nature plants have adapted to use many different nm of light, from dawn to dusk the light they receive is constantly changing, being scattered and altered by the atmosphere, by clouds, by other plants growing over them etc... The most important thing is that each plant gets enough light to grow. Similar to the planting directions that come with most garden plants (full sun, some shade, shade plant).

Learning about lighting preferences is, however, quite interesting. Kelvin rating can't be used to determine the nm output of the bulb. Kelvin ratings are derived from the average of all the wavelengths that the bulb puts out and the number of peaks it puts out. So any two bulbs may have the same kelvin rating but have totally different nm outputs. Essentially kelvin rating is how the bulb looks to the human eye, it is not a detailed measure of how much of each type of light is coming out the bulb like a spectrum graph shows.

If you add red lights and then add more white lights, then yes the color will be blended out, though I suggest you get the color light you like best and use that rather than the color that is theoretically best for plants.

Below I have summarized some information found in some sticky threads from the lighting forum. Most of the detailed information was originally posted by Newt. This is mainly for clarification and general knowledge more than anything.

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*Lighting Information:*

Found in this thread: 
http://www.aquaticplantcentral.com/forumapc/lighting/26955-color-temperature.html

For green plants the lighting peaks that are most important:
chlorophyll-a: 430nm/662nm
chlorophyll-b: 453nm/642nm
carotenoids: 449nm/475nm
Red pigmented plants use more light in the blue area of the spectrum.

The curves on the graph are geared more towards green pigmented plants as red plants do not absorb red light; it is reflected. All plants have both A and B Chlorophyll, the photosynthetic pigment used by plants traps blue and red light but is more efficient with red light at 650 - 675nm. Blue is used at the same rate as red because it is more available. Red plants need to utilize more blue light as the red is not absorbed.

Here is another graph that may help:









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*Comparisons:*
Found in this thread:
http://www.aquaticplantcentral.com/forumapc/lighting/723-9325k-difference.html
A comparison of different color bulbs on the same tank:

9325K bulbs








vs.
6700K









This is 2x 6700/10,000K with 2x 9325K lamps:








This is 4x 6700/10,000K lamps:









1x 5000 K & 1x 6700 k









1x 6700 k & 1x 9325 K









2x 9325 k


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## CatG (Apr 10, 2010)

Thanks for the info! I really appreciate your input!

Ok, so I guess I need to quit stressing about the exact NM, and just worry about getting lights that will get down to the bottom of my tank. I just worry alot because I don't have alot of money to spend, and can't afford to buy the wrong thing. I can't afford to buy duplicate light fixtures and plants because the first set didn't work. My first tank was/is a money pit, and this tank is even bigger which means even more money needs to be spent.

Thanks again,
Cat

Ps. At this point, if anyone can simply tell me what to buy that has been proven to work, I am all ears. lol


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