One of the more interesting tidbits of data is contained in the posting "Watts, lumens and hogwash" by Wright Huntley in the Sat, 9 Nov 1996 APD.
Lumens: This is the amount of light the bulb produces. Most flourescents are in the 2000 range. This doesn't matter too much though. As long as it is in this range it will be fine.
Lumens: A measurement of light intensity. (1 lumen=10.76 lux).
Lux: The standard for measuring light.
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Initial Lumens - Light output of a bulb at 100 hours or operation
Lumen - Measures light output
Kelvin - Scale used to measure the color of light ...
Lumens
This is the total amount of light a bulb is capable of generating and is perhaps the most important information you need to know from the manufacturer.
MH lumens per lamp = 36000 (Philips MH400/U, initial)
MH watts per lamp = 400 (ditto)
MH cost per lamp = ~$70 (from memory, Venture 5200K)
operate lamps 12 hours/day
replace lamps once per year
electricity cost = $.09 / KWH (your mileage may vary) ...
The Importance of Lumens
The sun is very, very bright. It shines very strongly on the tropical regions where the plants we have in our tanks come from. We measure that brightness in Lux, or lumens per square meter.
(No, I'm not being paid for this plug) Specifications: 5500 K, 91 CRI, 2180 Lumens. For folks looking for more luminosity Duro-Test offers another lamp, the Vita-Lite Plus; the only specification difference being the generation of 2,750 lumens.
Most high powered LEDs (the sort you use for growing plants) only use 2-4 watts of electricity and pump out anywhere from 100 to 300 lumens (for comparison a 70 Watt metal halide bulb produces around 5000-6000 lumens).
The next issue with aquarium lighting is the various terminology used in the hobby, such as color temperature measured in kelvins, color rendering index (CRI), photosynthetically active radiation (PAR) and lumens.
These scales may be narrow or wide as needed and covers a range from 0 (the lowest) to 10 (the highest). The range does not describe what those numbers correlate with in terms of lumens, watts, photosynthetically active radiation (PAR), or bulbs.
A bulb rated at 5000K is the color of midday sun, whereas a bulb rated 10,000k is very blue. Intensity (amount) of light is measured in lumens, but for simplicity we can use a bulb's wattage to gauge the amount of light it will produce.
They are very efficient in terms of lumens/watt. Do not confuse these with halogen bulbs, which have a very yellow light not appropriate for aquarium use.
 See also: Color, Lighting, Plants, Aquarium, Water
  
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