This post was originally posted on FTTV by Benjamin Peterson. it's a huge help in trying to figure out what lighting area you may be in. This is a link to a video which explains the chart and how to read it made by me (Shane) - http://www.youtube.com/watch?v=hAT1e6bsOrY - From here forward is a direct copy and paste of his post.

 

This was posted on Monterfishkeepers.com by jcardona1.

 

Ok, so we all know the watts per gallon (wpg) rule is pretty much useless these days with all the different types of lighting. there are other ways using lumen calculation but i still dont like this, and is usually pretty damn confusing.

a member on plantedtank.net put together a great chart, using real data gathered with different bulbs and a PAR meter. this is awesome, and is a great reference for seeing what catergory of light youre in when it comes to plants. or how many bulbs you'll need to be in a certain category.

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example, let's assume that i have a standard 55g tank(48x15x18). now, with a height of 18", let's say our light fixture will be 18" away from the bottom of the tank after taking into account your substrate depth of approx 2".

so based on this chart, if i were to run one T5HO bulb (assuming the bulb spans the length of the tank), this bulb would give me 65 micromols of PAR, which puts me in the MEDIUM light category. now if my fixture had two T5HO bulbs, just multiply the figure by 2, which gives us 130 micromols of PAR and well exceeds what is considered HIGH light. this may be too much lighting and could potentially give you algae problems. easy enought right???

same scenario, but let's assume we're using a standard T12 bulb. that gives us 10 micromols of PAR per bulb, which isnt even considered low light. we'd need 3-4 bulbs to be in the low light category. wanna be "high" light with T12 bulbs? gonna need at least 8 friggin bulbs!!!

now you see why T5HO are the most effecient and economical choice when it comes to lighting, especially for planted tanks.

so what do you guys think? can we put an end to all those wpg rules? i think this is easy enough, and should be a good guide for those wondering about lighting. afterall, the hardcore planted tank freaks ignored the wpg rule a long time ago!!!



here's the original quote, and full thread:

http://www.plantedtank.net/forums/li...t5-t12-pc.html

I have been wondering how much PAR a typical T12 light produces. Like most everyone else I have just assumed that watts per gallon was a way to guess the light from T12 bulbs, but there is no more reason to expect that to mean anything than there is to expect it to mean anything for other bulb types. So, I decided to do some testing.

I borrowed a new two bulb 48 inch T12 light fixture from one of our local aquatic plant club members, bought a new T12 bulb - a Phillips "Natural Sunshine", 40 watt 5000K, 92 CRI bulb at HD, borrowed our club PAR meter and took some readings. Since I have previously found that I get virtually the same readings with water in the tank and with air in the tank, I omitted the water this time. Then I plotted my smoothed data on a common plot with T5 and PC data:

To compare this with "watts per gallon", I know that a couple of 2 bulb T12 fixtures will grow plants in a 55 gallon tank. That tank is 20 inches deep, so if the substrate thickness is about the same as the height of the bulbs above the top of the tank, each bulb should give about 9 micromols of PAR, or 36 micromols for 4 bulbs. That is right in the middle of the low light range. So my data is consistent with real life results.

The light fixture I borrowed has an acrylic splash shield and a removable back, which is a white reflector. I tested the light with and without the splash shield to find that the shield reduces the intensity about 7%. Testing with and without the white "reflector" shows that the reflector increases the intensity by about 36%. The data used for the chart is with both the shield and the reflector.

Some popular tanks are only 12 inches high. For those tanks T12 bulbs should give about 25 micromols per bulb, so a 2 bulb fixture will give low medium light intensity, probably a good choice for many people with one of those tanks.

I believe T8 bulbs produce about the same amount of light as T12 bulbs, but at a lower wattage, because they are more efficient. The fixture I borrowed uses starters and magnetic ballasts, so I didn't try it with a T8 bulb.