How is light measured?
The Visible Spectrum of Light
Visible light is on a scale in nanometers from 400nm (violet) to 700nm (red).
The blue and red zones of the visible spectrum are the most beneficial to plants and algae.
Green plants appear green because they reflect the green part of the spectrum.
The human eye is most sensitive (brightest) in the green spectrum (middle of visible spectrum, or around 550nm).
CRI: Color Rendering Index
CRI is a measurement of how accurately a light source can produce colors in objects.
Scale is from 0 to 100 Natural Sunlight is 100.
The higher the number the more vibrant the colors will appear.
Have you ever bought a piece of clothing in a store only later to realize that in natural sunlight the color looks different, most likely the store was using low CRI Bulbs.
CRI has very little meaning to aquarium occupants as it is based on human vision.
The light that the human eye can see VS. The light that aquarium photosynthetic animals like
The lumen is a measure of flux, or how much light energy a light source emits (per unit time).
The lumen measure does not include all the energy the light emits, just the human visible wavelengths.
The lumen has very little meaning to aquarium occupants as it is based on human vision.
Lux = Lumens/Square Meter
Watt is a unit of electrical consumption, not of light energy.
The amount on energy that your lighting system consumes may have little to due with how much usable light is emitted.
The watts/gallon rule as applied to aquariums continues to be outdated as more efficient lighting source are able to squeeze more usable light from each watt.
This measurement can give you an idea how much light is produced if comparing apples to apples.
The Kelvin rating is a indication color temperature.
The Kelvin rating for light sources:
– 2,700K- average incandescent light bulb
– 5,500K – Daylight
– 10,000K – Blue Sky
It is the average of all the light emitted from the light source.
Two identical Kelvin rated light sources can be composed of vastly different wavelengths of light.
This measurement can give you a general idea of the color and composition of the light.
Personally I think some of the numbers stamped on the bulbs are just for marketing.
PAR - Photosynthetic Active Radiation or Photosynthetic Available Radiation
PAR accounts with equal weight for all the output a light source emits in the wavelength range between 400 and 700 nm.
PAR differs from the lumen in the fact that it is not a direct measure of light energy, but rather light energy that is useable for photosynthesis.
It is expressed in "number of photons per second".
The reason for expressing PAR in number of photons instead of energy units is that the photosynthesis reaction takes place when a photon is absorbed by the plant.
PAR is one of the most meaningful measurements to aquarium occupants (PAR figures are not listed on lighting systems, as they are setup specific).
Application to Aquariums
Fish only Tanks
From a color temperature standpoint (Kelvin rating):
Blue-colored light (10,000K) will enhance blues in your fish.
Green-colored light (5,500K – 6,700K) will make the tank look bright to humans and enhance the green color of your plants.
Red-colored light (2,700K) will enhance the reds in your fish, and any red plants.
The light cycle can be important to trigger spawning (or a change in the light cycle).
The amount of light can be used to control algae.
For green plants the lighting peaks that are most important:
– Chlorophyll-a: 430nm/662nm
– Chlorophyll-b: 453nm/642nm
– Carotenoids: 449nm/475nm
– Blue Green Algae (cyanobacteria), which contain Phycocyanin and absorb light heavily in the low 600nm (orange-red).
Red pigmented plants use more light in the blue area (450nm) of the spectrum.
If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum.
When light penetrates the ocean, the red spectrum is filtered out. (This is why the ocean appears blue).
Sunlight at the waters surface has a color temperature of 6,500K.
The light spectrum approximate a depth of 5 to 10m (16.5 to 33 feet) is 10,000K.
The spectrum is equivalent of light at a depth of about 20m (66') is 20,000K.
Most standard lighting is in the 6,700K range in order to get a (Higher Kelvin) rating Actinic (lighting that ranges from ~380 nm to ~480 nm, with a major peak at ~420 nm) bulbs are often used as a supplement.
Zooxanthellae(Zoo-zan-THEL-lee) are symbiotic Algae located inside various marine invertebrates (Corals, Anemones, and Clams) they can provide up to 90% of a coral’s energy requirements.
Zooxanthellae utilize Chlorophyll-a and Chlorophyll-c
The absorbance spectra for Zooxanthellae is much broader in the Blue spectrum (400 - 450nm).
Great Light & Free
Impossible to Control
The hardware is very cheap.
Most energy is wasted as heat only 17 Lumens per watt.
Incandescent has very poor quality of light typically 2,700K.
Compact Florescent is the spiral bulb now used to replace incandescent bulbs.
Uses less electricity
Ballast is not remote
Very high restrike
T designation is based on 1/8th of an inch
– T12 = 1.5 inches
– T8 = 1 inch
– T5 = .625 inches
NO - Normal Output
HO – High Output
VHO – Very High Output
Normal Output Fluorescent
NO is in a standard aquarium hood that is included in most aquarium combo setups.
It is also what is used in shop lights and most home installations.
T12 has a output of approx 55-75 Lumens per watt (magnetic or electronic ballast).
T8 has a output of approx 80-90 Lumens per watt (magnetic or electronic ballast).
T5 has a output of approx 95-105 Lumens per watt (electronic ballast only).
High Output Fluorescent
HO are basically the same as regular fluorescent except the ballast is designed to supply the bulbs with more electricity.
T5HO has a output of approx 85-95 Lumens per watt.
A 24 inch T5 NO is 14 watts.
A 24 inch T5 HO is 24 watts.
Power Compact (bent T6HO) has a output of approximately 75-85 Lumens per watt.
Higher restrike (when light hits another spot on the bulb and is lost)
Very High Output Fluorescent
VHO is basically the same as regular fluorescent except the ballast is designed to supply the bulbs with more electricity.
VHO has a output of approx 55-75 Lumens per watt.
A 48 inch T12 NO is 40 watts.
A 48 inch T12 VHO is 110 watts.
Spiral bulb now used to replace incandescent bulbs and has an output of approximately 70 Lumens per watt.
Ballast is manufactured to be disposable
Ballast is not remote - life is shortened due to exposure to heat and humidity.
Very high restrike
not a way to add a great reflector.
output of approx 50 Lumens per watt.
output spectra that is almost entirely blue-white, with very little red
High/Low Pressure Sodium
output of approx 100-150 Lumens per watt (currently the most efficient lighting system)
output is pure yellow (only good when used in conjunction with other types of lights).
New bulbs with increased Blue spectrum are now being used for terrestrial plants with great success, but have not been tried in aquariums yet.
Point source lighting is able to penetrate deeper aquariums (But lighting is less evenly distributed than with Fluorescents).
generates a lot of light in one spot, so more heat gets transferred into the aquarium water (fans and chillers may be necessary).
90 lumens per watt.
Dimmable many can reproduce sunrise and sunset (even the lunar cycle as well)
Longer life more than 50,000 hours
Virtually no heat transfer to aquarium water
Light is very directional (like laser pointer) optics(lenses) are necessary to spread the lighting
First led systems on the market are close to 90 lumens per watt.
Very Expensive Hardware.
A good quality reflector will direct approximately 20% more light that is already being produced down into the aquarium.
Fishroom w/ 1000+ gallons with a little of everything, OK well still mostly plants
Posted with David Stewarts permission