Hi Aaron
I have added a few more terms and explanations below that you may like to incorporate into your article. Some of this may have repeats of what you have covered above
Glossary
Lumens - Luminous power, measured in Lumens (lm), is the amount of ‘visible light’ (for the human eye) that is emitted by the light source.
Lumens/Watt - Luminous efficacy measured in lumens per watt (lm/W), is the amount of light given out for each watt of power usage. This can help compare lamps of different types and brands. As an example an incandescent bulb will have a lower luminous efficacy as compared to a fluorescent lamp. Some commonly used linear fluorescent lamp sizes in aquaria and their luminous power and efficacy is given below (taken from Sylvania catalog 2013)
Diameter
Length
Lumens (typical)
lm
Wattage (typical)
W
Lumens/Watt
lm/W
T8 – 26mm (1 inch)
18inch
760 lm
15W
50.67
600mm (24inch)
1250 lm
18W
69.44
1200mm (48inch)
2800 lm
36W
77.78
T5 – 16mm (5/8 inch)
24 inch
1200 lm
14W
85.71
34 inch
1900 lm
21W
90.47
SMD LED strips sold these days such as the 3528 give out 6lm and consume 0.06W, that’s 100 lumens/W. The 5050 is the equivalent of 3 x 3528 and gives 18lm and consumes 0.18W. Again note that 3528 is the LED size and you can find different types which give off more or less lumens that shown above.
Example: So if you are at present using 2 x 18W T8s and wish to upgrade to T5s then you would need to calculate as follows
2x18W T8 = 2x1250lm = 2500lm
a 24inch T5 gives out 1200lm so using 2 of those would give you 2400lm (thats slightly less light) but your overall power consumption would come down by 2x (18W-14W) = 8W.
You would need 2500lm/6lm = 417 LEDs of type 3528 to give you the same amount of light and these would save you around 11W.
PAR – Photosynthetically Active Radiation, is the light radiation in the range 400nm-700nm that can be used by plants to photosynthesise and measured in micro moles of photons. (Read the background information on light below for more information)
Watts (W) – amount of power consumed (electricity) by the lamp. Eg: a lamp rated at 40W will consume 40W per hour. Fluorescent tubes are categorized based on their diameter in 8ths of an inch. So a T5 is 5/8inch and T8=8/8=1inch. Tubes come with typical wattages depending on their lengths. So for a tube of length 18inch the typical wattage will be 15W, 2ft = 18W, 4ft = 36W and so on. The T5 range has wattages such as 8W for 1ft length, 14W for 24 inches length etc. These wattages are changing with recent improvements in technology and the power consumption is reducing.
Watts/gallon – This used to be the rule of thumb for measuring how much light was needed to grow a planted tank. Eg. 2W/gal of water was considered a minimum requirement for growing plants. But with the advances in technology and introduction of Compact fluorescent lamps (CFL), LED etc., this rule no longer holds true as the newer lamps consume a lot less power (W) and provide the same amount of light (lumens). Going forward, PAR gives a better indication of lighting requirements for planted tanks and lumens/gallon for tanks in general.
Background information on light
The sun is the main source of visible light and invisible electromagnetic radiation and the key factor responsible for the existence of life on earth. The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. The spectral distribution of the sun's radiation, as it can be measured at the earth's surface, has a broad wavelength band of between around 300 nanometers (nm) and 1000 nm. However, only 50 % of the radiation reaching the surface is photosynthetically active radiation (PAR). i.e. can be used by plants to photosynthesise. According to the CIE (Commission Internationale de L'Eclairage) recommendations, PAR comprises the wavelength region of between 400 nm and 700 nm of the electromagnetic spectrum. Plants use photoreceptors (eg.chlorophyll a/ b, phytochrome, cryptochrome) to harvest the energy. The two most important absorption peaks of chlorophyll are located in the red and blue regions from 625 to 675 nm and from 425 to 475 nm, respectively. Additionally, there are also other localized peaks at near-UV (300 - 400 nm) and in the far-red region (700 - 800 nm).
Human eyes can see in the range of 380 nm to 780 nm and hence lights which are sold for human use provide light in this ‘visible spectrum’. The light intensity for a typical Cool White fluorescent lamp has smaller peaks in the 420-440 nm (blue) and 630-640 nm (red) with the highest peak being in 550-560 nm (green –yellow) range. So the energy of the lamp is primarily emitted in the wavelengths which are pleasing to our eyes. Cool Daylight lamps have similar peaks but also radiate in other wavelengths thus providing a broader spectrum of light in an attempt to simulate daylight.
Plant lights (hydroponic) on the other hand emit their light in the wavelengths which encourage photosynthesis and look purplish to us.
And for those of you who wish to get more detailed information here are a few good sources:
General lighting article http://americanaquariumproducts.com/Aquarium_Lighting.html
Useful article on PAR http://www.plantedtank.net/forums/showthread.php?t=160396
Hope this helps enhance your article.
