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Re: Aquatic Plants Digest V3 #795
>Date: Fri, 22 Jan 1999 09:01:05 PST
>From: "Colin Anderson" <colin_d_anderson at hotmail_com>
>Subject: Chroma 50 and 'Plant Bulbs'
>Sorry, but I can't resist. Why would we use 'plant' light bulbs? IF
>LUMENS are in your equation at all...
>You bought the ballast, the fixture, whatever, paid your dues, now GO
>FOR THE LUMENS! If anyone would like to refute the arguement that
>nearly all light grows plants and that more lumens are better, I'd like
>to hear it :~>
Ok, you're asking for it.
Why don't you consider green laser. It has maximal possible lumen per watt
value. By definition 1 watt at 555 hm equals to 683 Lm. But, I don't think
plants would like this light.
To find lumen-per-watt value at any other wave-length you need to multiply
watts by human eye photopic response curve. Lumen value is lamp parameter
that tells how "bright" this lamp appears to human eye (we actually see
brightness, not lumen flux, but this is a different story). For, example
sun has about 100 LPW (and balckbody at 5500K, too). This can be calculated
by multiplying balck body spectral radiant poower curve by eye response.
So, lumens are useless if you talk about light that are used for other than
illumination for human eye purposes. Even more, the human has different
(scotopic) response curve at darkness. For, example, if you take red and
dark blue color, red appears brighter for than blue, but in dark room, blue
seems to be brighter.
Thus, if lamp is optimized for use with plant grow (it has two peaks at
blue and red and no or small green), then it has very low LPW. 20W Philips
Agro-Lite produce only 600 initial lumens. And average 20W fluorescent
lamp - around 1200-1600 Lm. You need to use PAR values or simply power in
watts in each spectral region. And you don't need to go for lumens. You
need lumens to illuminate plants/fishes so you can them well. You need
lumens only for you. FOr plants you need energy.
Next - CRI. CRI is charateristic of color rendering, the ability to
represent color of objects.
To calcultae CRI you need to compare the lamp and test-source. For example,
CRI of usual incandescent lamp is 100 (for source <5000K, test source is
special incandescent lamp, for source >5000K it is "dyalight" source). SO,
you can't even compare CRI of two lamps if they have different CCT.
Nothing comes free. Higher CRI means less lumens. Comapre LPW of typical
TL90 and TL80 lamp. Color rendering is important for human eye only. Plant
lamps have very poor CRI (they have no green, so they can't represent green
colors). But plants don't care about CRI. You care, because you want your
plants/fish look natural (what does natural look mean?).
CCT - same problem. Lamp color can be described by it chromatiicity, two
color coordinates - 'x' and 'y'. You may wish to check any good
photomtery/color book/Inet site to look at color triangle. This two
parameters define completely color of lamp. But, we don't like two numbers.
We want one (so, companies can promote their lamps - 5000K, 10000K,
20000K...it's difficult to say what is better x=0.434, y=0.356 or x=0.465,
y=0.324). So, CCT was introduced. This is temperature of blackbody that has
closest chromaticity. Actually, it doesn't say how close. You can make lamp
with CCT=100000 very easily. Just stick blue filter before incandescent
lamp. Two lamps with same CCT may have different colors. Basically, as
higher CCT (after 5500K) as lower LPW. This is because balckbody at
5000-6000K has maximal LPW - our eye is optimized to sun spectrum.
Finally, as long as your lamp has blue and red (that measn higher PAR
value), plants gonna like it. Even combination of daylight (it has blue)
and incandencent (or low CCT ceramlux lamp) will work OK. You need high
CRI lamps for you, not for plants (yes, high CRI lamps has blue and red,
it's necessesary to get high CRI, and plants like them).
About, gettins twice more lumens/energy from lamp. Even aquarium keeper
should remeber about energy conservation law. If you put 4 lamps with
1500Lm (or 150 w) each, you never (I even don't like hear if anyone
disagree:) can get more lumens, by using reflectors. You can try to recycle
light and shift its frequency toward green and gain more lumens per watt,
but this is different story. Why people tell that reflector help get more
light. It's easy. When catalog says that lamp produce 1500 LM, this means
light goes in all directions. You need light that goes in certain direction
(down). So up-going light is lost for you. You can use less than 50% of
light without reflectors. Lets' say you place lamp 6 from water surface and
tank is 12" wide. Only light within 90 degree angle is used = 25% of light.
Only 375 Lm hits the water. Even less light reaches the bottom. You can use
reflector. Good ALZAK aluminum reflector has reflectance of 90-95%. Nickel
reflector98%, but it costs $$$$$$$$ Cheap foil probably has 80%
reflectance. By placing foil above lamp you can redirect 20% more light (so
you get twice more light at water surface). By using special designed
reflector you can collect about 60-70% of lamp light. Maybe even more - I
should play with numbers on my computer - I would use kind of shallow
parabolic or shape similar to big 'M' letter. With more than one lamp
reflector efficiency drops, because lamps blocks light. BTW, this can cause
lamp overheating and drop in light output and life. The optimal solution
would be use of aperture lamps. I saw these lamps in catalogs, but never in
>This data is from the krib, take a look at:
Take a look at:
www.philipslighting.com - they put recently catalogs and information
literature on their homepage.
www.ge.com and so on
>Get Your Private, Free Email at http://www.hotmail.com
Michael, who makes his living by designing weird shit around weird lamps.