The bottom line is when you compare an LED Aquarium light to the many popular CFLs and even T5s in terms of lumens per watt, focused lumens, PAR, PUR, lower wasted yellow/green light energy, low heat output, energy consumption, long life (25,000 to 50,000 hours vs. 8000 hours), the modern recent generations of LED Fixtures are generally the best available aquarium light.
This includes the patented emitter ultra premium high PUR per watt AquaRay AquaBeam or GroBeam LEDs as well as the still VERY capable Aqua Illuminations, EcoTech Radion, ZetLight (aka Maxspect), and few others.
Most premium LEDs are a better light even in long term cost since (as an example) a 12 Watt Aqua Ray GroBeam 6500K daylight (either #600 Strip or Mini #400 Tile) can easily replace a up to a 80 Watt power compact (also daylight) when you compare ALL aspects of lighting as presented in this article.
Another misunderstanding about LED emitters is targeting the responsive wavelength. While exact coral responsiveness wavelengths are unknown, much is known in a more broad sense (and even more knowledge is growing, such as the "blue band" of coral responsiveness). For example, we do know that much of the yellow and green bands are 30%-80% less efficient for most photosynthetic corals, clams, etc. (although under 24% green light can be useful, but over 25% it is actually detrimental; Reference: )
All electromagnetic radiation travels through a vacuum at the same speed, called the speed of light. Its speed in any given medium depends on its wavelength and the properties of that medium. At the surface between two media, like any wave, light can be reflected, refracted (its path bent), or absorbed. What occurs depends on properties of the surface and the wavelength of the light. When shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) is absorbed in matter, it can ionize atoms and cause damage to living cells. However, because X-rays can travel through soft body matter for some distance but are more rapidly absorbed by denser matter, particularly bone, they are useful for medical imaging. Photovoltaic materials emit electrons when they absorb light of a high-enough frequency. This phenomenon is used in barcode scanners and “electric eye” systems, as well as in solar cells. It is best explained using a particle model of light.
Any flaws of LED aquarium lights are quickly disappearing and based on the energy savings for the premium high PUR LEDs with PWM technology as compared to MH.
In fact for Planted Freshwater the top LED Lights (with the highest PUR) have few limits in their applications.
When compared to even older T8/T12 aquarium lights, a forth generation AAP AquaBeam & GroBeam LEDs require only 15% (or less) of the wattage for the required light energy of a planted or reef aquarium.
This is as little as .6 watt per gallon for high light planted aquariums and .8 watt per gallon for Reef for the AAP AquaRay and 1.25 -1.5 watt per gallon for the ZetLight, EcoTech & Aqua Illuminations, and 1.75 -2.25 for many other LEDs such as the Ocean Revive, Taotronics, etc. (Acroporas may require a higher wattage input per gallon)
, keep in mind that a PAR Meter is NOT accurate in important light energy spikes WITHIN the 400 to 700 nanometer range, so while one light might measure a higher PAR mmol reading, another light might be still superior due to the more important PUR & PAS output.
This is where I have found the use of a PAR Meter SOLELY to determine light efficiency over rated.
When the PAR distribution throughout the canopy as altered by the kaolin application was used to run the models without accounting for the shading effect of kaolin on the individual leaves, the PRUE estimated with the 50-leaf model was 7·5 % greater than that predicted by the simple method (i.e. E50L,R100 = 1·075EHL,R100; Figs B and ). This increase was an artefact, since the PAR used in this exercise was that measured by the sensors without correcting for the shading effect of kaolin on the leaf. However, this exercise showed that the PAR distribution as altered by the kaolin application had the effect, per se, of increasing canopy PRUE. In fact, since the two models yielded similar values of PRUE before kaolin application, we can assume that EHL,R100 represents the PRUE that the canopy would have had on that day if kaolin had not been applied. Consequently, the 7·5 % increase in PRUE estimated with the 50-leaf model was entirely due to the altered PAR distribution within the canopy caused by kaolin application. The positive effect of the altered PAR distribution on PRUE can be explained by considering that kaolin application decreased the light incident on outer-canopy leaves and increased it on inner-canopy leaves (Fig. ). In fact, top-canopy leaves often operate near light saturation and their PRUE is improved at lower light, while inner-canopy leaves operate more often at low light and their PRUE is improved at higher light (). Skewing the light distribution towards inner-canopy leaves, as kaolin application did (Fig. ), would therefore result in improved canopy PRUE, as previously found in Prunus under water stress () or as commonly found with diffuse light, which penetrates the canopy better than direct radiation (; ).
In conclusion, the smaller reduction of canopy PRUE (i.e. 6·3 %) compared with the 20 % reduction in leaf absorptance was due to two main factors. The first was that reducing PAR decreases photosynthesis less that proportionally (in our example the reduction was 11·3 %). The second factor is that kaolin application favourably alters the light distribution within the canopy, so that the final loss in PRUE is even less (in our example it was 6·3 %).
Further PAR Information;
As a light energy penetrates deeper through water, these need to move slightly "left" (lower) on the nanometer graph so as to allow for optimum use of PAR (in other words Photosynthetically useful radiation; please see the PUR/PAS section).
Some organisms, such as Cyanobacteria, purple bacteria & Heliobacteria, can make use of the unusable light discarded by the plant kingdom, in this case, light outside the PUR range required by plants, which is why Cyanobacteria thrive in lighting conditions that include more yellow light energy.
Many recent studies have shown the importance of full spectrum lighting as it relates to health in humans & animals, can be extrapolated to fish as well for a disease prevention which is why good lighting should not be restricted to Reef Marine or Planted Freshwater Aquariums, but to fish only salt or freshwater tanks as well.