It was only a few years ago that the upper limit of "low light" was about 2 wpg of NO (T12 normal output) light. Now we use not only T12's but also T8's, T5's, metal halides, and screw-in "compact fluorescents", among others.

There have been disputes over the the proper amount of lighting in which one party would say that 1.5 WPG was enough for a certain environment while another would be in favor of 3.0 WPG for the same environment. Each was thinking about a different kind of bulb.

So: Assuming the same environments (reflectors, water clarity, bulb age, etc.), how does the amount of useful light energy produced compare for the several kinds of bulbs that we have available?

Thanks.

Bill

Well, even if the bulbs are the same units, the tanks and their plants and other factors are not

However, at least having them in the same units as far as plant useable growth is concerned would be much more useful.

I chose PAR units and use a light meter.
I can/could measure anyone's set up or bulbs to compare against easily and quickly.

I measure the plants at the tip mid and bottom to get an idea of the light and this includes angle and other factors. It's not hard to do.

What is hard is assuming lots of things in order to get these lights all on equal terms.

I'd say there's a 2-2.5w/gal vs 1.5 w gallon with reflectors and nice T5's vs FL's, maybe slightly more.

Still, the standards folks use these days are PC/T5's.

So lowering the W/gal rule is likely better than raising it as many seem to suggest.

Regards,
Tom Barr

Thanks, Tom.

The WPG rule has been amply criticized and properly so. However, it has become a de facto standard because it is, or was, readily available and easily understood.

Now, while experienced folks seem to have adapted to a lower WPG for different lighting sources, I think you can imagine the confusion on the part of a newcomer when one person tells him that he needs 3 WPG and another, 1.5 WPG.

Are we saying something like "3 WPG T12 = 2.7 WPG T8 = 1.5 WPG T5?"

Also, where do the spiral screw-in CF's fit in? Watt for watt, I'd guess somewhere between the T8's and the T5's, but that is a big range.

I also have the impression that a spiral CF puts out much less usable energy than does a T5 of similar lumens rating, because of light bounce-back inside the reflector, like about 40 percent less. Is that right?

Thanks.

Bill

Your thoughts are certainly correct.

My thoughts are more about resolving these issues.
Unfortunately there are no simple ways to do it that are cheap and easy.

I use a light meter.
That solves my problem, but does not solve other folks who cannot or will not use a light meter.

I can make a large survey of various lights on folk's tanks, but glass, lids, depths, plant species, other factors involved other than light play a role.

The screw in bulbs have restrike issues.
T5s and MH's are the best highest watt/PAR available.

You can use 1-3watts/gal for those bulbs on most standard sized tanks as a rule.

2w/gal is still plenty to grow anything though.
And certainly so with T5's.

Regards,
Tom Barr