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How to read spectrum curve ?

eminor

Member
Joined
5 Feb 2021
Messages
784
Location
France
Hello, i know that plant can grow with any light, bulb i'd like to know what kind of color is that light ? thx

940.png
 
Hi @eminor

Are you asking about the spectrum shown in each of those above, which are identical? These show the spectrum of a fluorescent light with a lot of blue light, somewhat less green and a fair amount of red light. I would expect the resulting spectrum as perceived by the human eye to be pink with a touch of green. But, perhaps this is not what you are asking about?

JPC
 
Hello, i know that plant can grow with any light, bulb i'd like to know what kind of color is that light ? thx

View attachment 175584
The best way to interpret a spectrum curve is to imagine turning it upside down and that the outline of the curve is the outline of a bucket. The bucket holds colored water. The color of the water is based on the wavelengths.
To the far left is violet.
From about 300 to 400 is blue.
From 400 to 500 is green.
From 500 to 550 is yellow.

In the two identical curves shown, you can now imagine flipping them upside down. How much water would be held by the bucket from 300nm to 550nm? Well, hardly any blue water and zero violet water, but a relatively high amount of green and yellow water (can you see the bowl from 400nm to 550nm?)

There is another bowl from 550nm to about 650nm. In this range the water is colored orange turning to pink. From 650 to 750 is deep red, but that bowl is shallow.

So to answer the question of how the bulb should look to you when energized, it will be predominantly green/yellow/orange. This might therefore be a florescent bulb used in office spaces or in department stores. These typically have plenty of green/yellow, which we are most sensitive to - so the luminosity to us will be high but it wont actually be green to look at. It might have more of an orange/yellow tinge. When shone in a tank the green plants should appear bright and fresh. Red plants and fish with red coloration will also be accented, however, if used exclusively, the tank may have a very slight orange cast.

I've actually used T5 bulbs like this because they can be found everywhere - and are therefore cheap (yay!). No point in wasting money on stupid and outrageously priced "plant bulbs". Those bulbs just have more blue content (big deal).

You might have intended to attach two different spectrum curves? It doesn't matter. As I've described, this is the simplest way to imagine the visual impact of bulbs.

A lot of hobbyists mistakenly look at the high peaks and assume those peaks are the predominant color impact of the bulb. Those sharp peaks however, are meaningless. It is the area under the curves that determine the overall color content of the bulb.

Cheers,
 
Another way..Since the x axis was really poorly defined I went off the known mercury emission bands.
Soo not perfect but well in the ballpark.
mystery2.JPG

* MIXING LIST
----------------------------------------
myData mystery.txt [130°] x1
----------------------------------------

* SIMULATION DATA
----------------------------------------
Luminous flux : 500 lm
Radiant flux : 1,360 mW
PPF : 6.1 umol/s
TCP : 3970 K
CRI : 82

λp : 544 nm
Color : #FFB47B
----------------------------------------

* PERFORMANCE @ 60cm
----------------------------------------
Irradiance : 0.3 W/m²/s
Illuminance : 96.1 lx
PPFD : 1.2 umol/m²/s
----------------------------------------

by SPECTRA 1.0β @ 1.023world
 
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Amazing tips, thanks so much, you were right, i got the light today, lot of yellow and green in it =)
 
Amazing tips, thanks so much, you were right, i got the light today, lot of yellow and green in it =)
Just a point that should be mentioned regarding the above color graph.
As you may notice the shadowy grey area is the curve used to define the CRI standard used.
CRI is a pretty flawed metric but it will give you a base understanding of how accurate color are to a certain standard.
In the above the CRI calculation is based on a tungsten light, thus the smooth grey slope in the background.
Compared to using the "daylight" standard (D50, D65, or "C".. don't ask) the color fidelity will be lower in this case.. to about 70.

Might as well go full geek here..an interesting historical perspective:

And a rough idea of how CCT (K) affects colors:

Also keep in mind Lumens/watt is not PAR/watt.
Lumens for you, PAR for plants.
 
thx guys, i know that any bulb can grow plant, but i've read that lower than 4000K caused certain types of algae is that another myth ? can i go lower than 4000 ?
 
i know that any bulb can grow plant, but i've read that lower than 4000K caused certain types of algae is that another myth ?
Yes.
can i go lower than 4000 ?
Yes. Its really important to realize the truth about light bulbs. Only use bulbs that make the plants and fish look pretty.
If you insist on using bulbs based on some urban myth about Kelvin temperatures you may wind up using bulbs that make the tank look ugly - and that's just not enjoyable at all. Kelvin ratings are all simply marketing devices. You can buy 5 bulbs with the same Kelvin rating and they will all look differently. Consider therefore that these ratings from different manufacturers should be thought of in the same way you think about model numbers of cars or washing machines.
Combine different color bulbs to achieve the visual artistic rendering that you desire and forget about all the technobabble.
Have a look at the sticky in this section for a visual reference=> Cheap HO T5 fluorescent tubes - Update with photos

Cheers,
 
Yes.

Yes. Its really important to realize the truth about light bulbs. Only use bulbs that make the plants and fish look pretty.
If you insist on using bulbs based on some urban myth about Kelvin temperatures you may wind up using bulbs that make the tank look ugly - and that's just not enjoyable at all. Kelvin ratings are all simply marketing devices. You can buy 5 bulbs with the same Kelvin rating and they will all look differently. Consider therefore that these ratings from different manufacturers should be thought of in the same way you think about model numbers of cars or washing machines.
Combine different color bulbs to achieve the visual artistic rendering that you desire and forget about all the technobabble.
Have a look at the sticky in this section for a visual reference=> Cheap HO T5 fluorescent tubes - Update with photos

Cheers,
damn the industry is so f*cked up, that's why i prefer a 6500k over another 6500k i thought it was in my head "it is actually =)"

another question if i may, I have an odyssea t5 fixtures with parabolic reflector, it may be a dumb question though, is that normal that the light color seems to change if i switch the tube position ? what if i make space between them because now there is 3 cm between them ?

lets say that i have 6500k in front and 4000 in back, on my fixture if i want the 6500k to appear more on the front of the aquarium i need to place it in the back i think that's because of the parabolic reflector right ?
 
damn the industry is so f*cked up, that's why i prefer a 6500k over another 6500k i thought it was in my head "it is actually =)"

another question if i may, I have an odyssea t5 fixtures with parabolic reflector, it may be a dumb question though, is that normal that the light color seems to change if i switch the tube position ? what if i make space between them because now there is 3 cm between them ?

lets say that i have 6500k in front and 4000 in back, on my fixture if i want the 6500k to appear more on the front of the aquarium i need to place it in the back i think that's because of the parabolic reflector right ?
Well that's a very difficult question because each fixture is built a little differently and the angle that the reflector is positioned differs. So the light can be made to cast slightly more adrift of vertical. I've not experienced the condition you describe. If I have a blue light in the front and an orange light in the back I see more orange in the back and blue in the front. You may be seeing reflections of each colors based on the objects in the tank. The light also exits the bulb in the shape of a cone and at some depth the two cones will intersect causing blending. The water bends each color a little differently and so does the glass. So you may be seeing composite colors and your brain will filter out blues and reds more strongly than oranges, yellows and greens.
At the end of the day you just need to place the bulbs in a position that you find most pleasing. Also, try different bulbs when you can buy them cheaply. I'm sure you will find combinations that you like if you experiment a bit. This is really part of the fun.

Cheers,
 
Well that's a very difficult question because each fixture is built a little differently and the angle that the reflector is positioned differs. So the light can be made to cast slightly more adrift of vertical. I've not experienced the condition you describe. If I have a blue light in the front and an orange light in the back I see more orange in the back and blue in the front. You may be seeing reflections of each colors based on the objects in the tank. The light also exits the bulb in the shape of a cone and at some depth the two cones will intersect causing blending. The water bends each color a little differently and so does the glass. So you may be seeing composite colors and your brain will filter out blues and reds more strongly than oranges, yellows and greens.
At the end of the day you just need to place the bulbs in a position that you find most pleasing. Also, try different bulbs when you can buy them cheaply. I'm sure you will find combinations that you like if you experiment a bit. This is really part of the fun.

Cheers,
thanks yes bulb is so cheap, 2$... should i take CRI seriously or is just another trap ?
 
thanks yes bulb is so cheap, 2$... should i take CRI seriously or is just another trap ?
Well CRI is really for your benefit.

Please note that the cri measurement has significant failures with leds and is being replaced by " better" descriptive metrics
That geekyness aside and more to the point cri can enhance your viewing enjoyment.
There is a sort of exception here that certain combinations of lights have lower cri yet are visually appealing.
Some rgb led arrays and combinations of " colored" t5s fall in this category with lowish cri but exaggerated reds greens ect for visual appeal.

Last thing is cri measurement is measured against different standards depending on the K temp. Approx 4500-10000(or more) is compared to daylight. Less than 4500 is compared to a tungsten lamp.

Back to the orig. question if using just white light sources cri could be important to you.
High cri with lights of k temps in the " daylight" range are more visually appealing and natural.

There are exceptions of course but not so much in white leds afaict.
 
Just a point that should be mentioned regarding the above color graph.
As you may notice the shadowy grey area is the curve used to define the CRI standard used.
CRI is a pretty flawed metric but it will give you a base understanding of how accurate color are to a certain standard.
In the above the CRI calculation is based on a tungsten light, thus the smooth grey slope in the background.
Compared to using the "daylight" standard (D50, D65, or "C".. don't ask) the color fidelity will be lower in this case.. to about 70.

Might as well go full geek here..an interesting historical perspective:

And a rough idea of how CCT (K) affects colors:

Also keep in mind Lumens/watt is not PAR/watt.
Lumens for you, PAR for plants.
@oreo57 do you work in print/photograghy industry or embedded vision?
I got a chuckle when you started talking about D50s
 
@oreo57 do you work in print/photograghy industry or embedded vision?
I got a chuckle when you started talking about D50s
I've dabbled in photography and have done work in graphic arts...
D50 ect also goes with computer monitors and displays ect.
 
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thanks yes bulb is so cheap, 2$... should i take CRI seriously or is just another trap ?
As oreo57 mentions, it is really only valuable as regards photography. It is not really something that we need to worry about. I never consider CRI or any other parameter of light bulbs other than turning them on over the tank and determining for myself whether I like the effects or not. As I mentioned previously, the bulb is nothing more than a paint brush.

Here is a typical example. The plant in question here is a version of Ludwigia (glandulosa) that has red, but the bulbs I was using had a lot of blue, so the color of the plant seemed OK, but nothing special:
9513675453_e8b57a7f1e_c.jpg


I replaced the bulb that was nearest the plant with a bulb similar to the one you mention in your original post which contains orange and some red:

9516464264_0dccecd6ac_c.jpg


I preferred the look of this bulb regardless of it CRI or other parameters. So really, who cares what the CRI number is?
The only thing that matters is whether you like what you see in the tank.

Cheers,
 
As I mentioned previously, the bulb is nothing more than a paint brush.
...that emits light and enables photosynthesis to occur. It also acts as the catalyst in the photoreduction of iron, etc. For anyone interested in reading further, you may want to take a look at the work of McCree, Govindjee, Emerson, Bruce Bugbee and Diana Walstad, to name a few.

Well CRI is really for your benefit.
:thumbup:

JPC
 
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