Question about light bulbs and WPG rule
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Question about light bulbs and WPG rule

This is a discussion on Question about light bulbs and WPG rule within the Beginner Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; --> Hi. Here is my question. Someone on this forum long time ago...about a year ago to be precise, told me that WPG rule no ...

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Question about light bulbs and WPG rule
Old 04-14-2009, 03:53 PM   #1
Unrulyevil's Avatar
Lightbulb Question about light bulbs and WPG rule

Hi. Here is my question.

Someone on this forum long time ago...about a year ago to be precise, told me that WPG rule no longer applies since it is a old rule and since then technology has moved on and that is right now you need to look only at the temperature in Kelvins when you are choosing a lamp (bulb)

To you knowledge ladies and gentleman ... is it true? Can I safely dismiss WPG rule? or not?

Thank you.
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Old 04-14-2009, 06:09 PM   #2
Yes as No

It really depends on what type of lighting you are using. It still works fine with T8 and PC florescents. It was designed using these types of lighting. It doesn't really work w/ any of the newer stuff like T5's
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Old 04-14-2009, 06:39 PM   #3
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There are really two issues with lighting; color and intensity. The color is rated using the Kelvin scale. Most agree that a K rating of 6500K or 6700K provides the best color to represent sun light at mid day. Plants seem to do best with this color of light.
The intensity is what WPG addresses. But with the change in lighting fixtures (i.e. Compact Fluorescent, T-5, T-8, etc) a better measurement is lumens. But even with that there are other factors that go into what the appropriate lumen value should be for each tank. They include tank depth, surface area, plant species, Co2 levels, etc. Leaving the light on longer does not fix this. Think about how long you'd have to stay in the New York sun in January to get a tan in versus in July.
So what's the best lumens value for you? It depends.
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Old 04-14-2009, 09:06 PM   #4
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The WPG rule only applies to T-12 bulbs. A 4ft T-12 bulb usually is 40 watts and is the baseline for the rule. However T-8 bulbs provide roughly 30% more light(lumens) with less wattage than T-12s. So a 4ft T-8 that is only 32 watts will provide what would be equal to 52 watts (according to the rule). T-5s and PC lighting doesn't have quite the output per watt as the T-8's, however you can fit more wattage into the same space, so it has its tradeoffs. Then you have Trichromatic bulbs which provide the same amount of lumens as a normal bulb, but has higher intensity of certain color ranges. My personal opinion is that if you are looking for say...3WPG and you were going with T-8 Trichromatic, you could get by with 1.5-2WPG and have the same light intensity that you are looking for.
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Old 04-14-2009, 09:11 PM   #5
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Also, the original WPG rule I believe was for tanks that were no more than either 16" or 20" tall(I can't remember now), so if you have a deeper tank, you can't calculate your lighting needs based off of T-12 lighting anyway. I don't remember where I read it, but I remember some article having calculations for adding watts/lumens per every 6" of tank depth....
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Old 04-14-2009, 10:06 PM   #6
Kelvin temp IMO doesn't matter too much. I pick lights with kelvin temps that look good. Personally I don't like 6700K bulbs or any similar temps. They look too green to me. My favorite bulbs are 9325K bulbs, they are amazing! They bring out colors really well, and have a nice white light. I've never had any problem growing plants under then. My avatar pic is under 6700K, while my sig pic is under 9325K.
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Old 04-14-2009, 11:08 PM   #7
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That is quite a few interesting points you guys made here.

Could there be too much light for a tank? Let's say we are taking about regular 29 gallon tank. What would be direct result on the plants in the tank with too much light? Algae?
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Old 04-15-2009, 12:31 AM   #8
well if you go over say 2 wpg I would suggest supplement co2. Basically the more light you have, the more control you need over the tank. Things like pressurized co2 and EI ferts become necessary. I've seen tanks run some really strong lights, up in the 4 wpg range. Going much higher IMO would just be a waste of electrcity.

I think it is possible to have too much light on a tank, but you would need some really high lighting. I doubt the plants would be too effected, but the tank would probably be unstable. You would most likely get sudden algae blooms.
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Old 04-15-2009, 12:15 PM   #9
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The previous posts have contained much good information. I only want to follow-up on Mikaila31's thought about too much light.

From my research I would conclude that the limiting factor for plant growth in a planted aquarium should be the light, as opposed to nutrients or CO2. Too little light and plants will fail to thrive and grow, too much and the plants will use all the available CO2 and algae will flourish because it is better able than plants to get carbon from bicarbonate. Without CO2 addition, no more than 2 watts of full spectrum light should be over a tank. As noted preivously by others, this can be calculated for the newer type of compact bulbs.

Like Mikaila31, I strive to get the "colour" that I prefer, using a mix of flourescent tubes (2 over each tank) but all full spectrum or versions of full spectrum. The cast of my 90g is slightly different from my 70g because of the second tube (one is always straight full spectrum). I have about 1w per gallon (80w over each tank), on for 13 hours each day, plus some daylight in the room. I do not add supplemental CO2. I use liquid fertilizer twice a week (leaves definitely start yellowing and becoming transparent if I only fertilize once a week--I've twice experimented with this in the last 6 months), and there is no algae to speak of. I've managed through good luck to strike the necessary balance between available CO2, nutrients and light. You can see how this looks in my aquarium photos.
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