*Phototropic response; having a tendency to move in response to light. Basically this is the Chlorophyll containing plant or algae "moving" to respond to a positive light source to begin the process of photosynthesis (initial growth of plants, zooxanthellae, etc.).
CO2 causes the lower atmosphere to be opaque at the main absorption bands. The mean free path is only about 25 meters, so at these wavelengths the lower atmosphere is already like a thick fog where IR radiation is scattered in all directions. As we rise up in the atmosphere so the density falls exponentially and only at heights of 8-9 kms does the atmosphere then become transparent in the main CO2 bands allowing energy loss direct to space. Doubling concentration rises that level nearer to the tropopause which radiates at a lower temperature. The estimate given for the Earth’s warmng in Houghton’s book is 1.2 degrees for each doubling – so 2.4 degrees would be the heating if CO2 concentrations were to increase by a factor 4. These figures are based on a radiation reduction of 4 watts/meter**2 caused by this effect of the effective radiation level rising to a colder level. In his book Prof. Houghton says this can easily be proved, but I have not understood where this figure comes from nor how it has been calculated.
Since it is well established that a photon is a photon and it is the quantity that certainly makes the most difference (PAR is quantity), we still cannot ignore the quality of the photon of which the only difference of a photon is the wavelength and frequency (energy).
The first graph shows how red, green, & red light growth based on weight of lettuce. It is clear from the picture that the green light is only 50% of the efficiency of red & only 20% of the efficiency of blue.
The second photo demonstrates how one light (the Metal Halide) has much more input energy (joules) and even after the known massive loss of input energy, it still has more photons (expressed as lumens here) than the 6500K Generic Gro Light LED, yet the outcome of growth is dramatic!
The picture to the left demonstrates this with two 15 Watt CFL (30 watts total) vs one 3rd generation 12 Watt Marine White LED (daylight 14,000K).
This picture is taken with a camera that filters out certain wave lengths allowing for a better viewing of the difference, which is otherwise not easy to discern. However, the picture shows how the LED on the left has less of the less efficient yellow & green than the CFL lights on the right.
Otherwise the light output appears the same, although this is still important when you consider, this is achieved with only 12 watts of LED vs 30 watts of Compact Fluorescent lights.
The picture below shows a spectrograph of two 6500K aquarium lights. One is an AAP AquaRay GroBeam and the other is a 6500 Aquarium CFL. The LED is rated at 12 watts while the CFL is 13 watts.While similar, it is clear to see the LED has more blue and a lower blue NM (fuller blue spectrum) amount as well as more red, less green, and the same yellow.The point this makes/demonstrates is that while both lights are rated as 6500K, they are still not the same in their light energy output. Even among LED lights we can have differences of spectrographs depending upon emitters used.
Think about how mixing all paint colors will produce black, while the mixing of all light energy produces white. We as humans may notice this to some degree, however we do not have the ability to pick out particular colors such as a honey bee can. As well, photosynthetic aquatic life also has differing abilities to pick out the needed light energy for life processes and even though the PAR readings may be equal, the light energy that provides this overall PAR or kelvin "color" is NOT.A Couple more points to better explain the concepts of PUR, "Useful Light Energy", or "Quality of light per application".
For further reading about PUR:*Below is a picture of a Reef Aquarium (88x32x24) that includes Acropora corals lighted with ONLY VERY high PUR but lower wattage AAP AquaRay NP 1500 & 2000 LED lights (this tank has been running with these lights for 6 months at the time of the picture).
Many people will think PUR is good in theory, but think it cannot be applied to every single species we are trying to grow under water. While we don't know every species and it's preferred nm of light prefers, we do know the light, which triggers photosynthesis in an organism as well as efficiencies based on real world tests.
*Chlorophyll B; The chlorophyll that occurs only in plants & green algae. It functions as a light harvesting chlorophyll pigment that pass on the light excitation to chlorophyll a. It absorbs well at wavelength of 450-500 nm & 600-650 nm
Since many photosynthetic organisms live where light in higher spectrums of PAS such as 600nm & higher penetrate less if at all (in particular algae, zooxanthellae, & cynaobacteria), many have adapted to ways to still harvest this light energy.
These organisms use Phycobilisomes which are light harvesting antennae of photosystem II (Chlorophyll synthesis in the Photosynthic Action Spectrum-PAS).
*Chlorophyll A; A type of chlorophyll that is the most common photosynthetic organisms predominant in all higher plants, red & green algae higher plants, red & green algae. It is best at absorbing wavelength in the 400-450 nm & 650-700 nm
PAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers that is generally accepted as needed by plants & symbiotic zooanthellic algae for photosynthesis (Zooxanthellae are single-celled algae that live in the tissues of animals such as corals, clams, & anemones).
It is also noteworthy that while outside of the accepted PAR, a study using infrared (IR) LEDs of 880 nm & 935 nm on etiolated oat seedlings showed leaf emergence, so these parameters may someday need better defining (See at the end of article).
Below 400 nm, there is the risk of photooxidation that generates toxic radicals, which can destroy the cell’s chlorophyll and other cellular components. Under intense UV radiation, violaxanthin (which is involved in photosynthesis) is converted via the xanthophyll cycle into zeaxanthin. In doing so, it receives excess energy from chlolorphyll and releases it as heat. This process thereby offers the plant photoprotection.
PAR is an important and accepted starting point to estimate light energy for our photosynthetic aquarium keeping needs. We measure PAR via µMolm which is a unit of measure (more about measurement later).
The effect of wavelength (color) on photosynthesis rate
Aim- see plan
Prediction - see plan
Apparatus - see plan
Method - I fallowed my method exactly.
It is also noteworthy that many "terrestrial plant lights" as well as many aquarium plant lights (often of lower in kelvin temperature) have more "red nanometer spikes" than higher kelvin 6500k, 10,000k & higher lamps.
The problem with these lights is that while all plants utilizing photosynthesis require the same essential ABCs of PAR (see the PAR section), the facts of light energy penetrating water requires higher kelvin (6500k +) be added to provide maximum PUR (see Useful light energy/PUR section). Aquatic Plants and corals have adapted/evolved to the natural light energy at certain depth of water and the misguided attempt to adapt these terrestrial plant lights is not going to be 100% effective as a light with more water penetrating blue & slightly lower red nm energy.
Above 700 nm, the photon energy is too low to activate the photosynthetic process via the chlorophylls and various cartenoids. However, the phytochrome photopigment, which is responsible for stem elongation, leaf expansion, shade avoidance, neighbor perception, seed germination, and flower induction, has two isoforms called Pr and Pfr. In its ground state Pr, phytochrome has a spectral absorbance peak of 660 nm. When it absorbs a red photon, it converts to its Pfr state, which has a spectral absorbance peak of 730 nm. When the phytochrome molecule absorbs a far-red photon, it converts back to its Pr state, and in doing so triggers a physiological change in the plant.