There are now T5VHO fluorescent bulbs that put out more light than MH/HPS but they are expensive. The T5HO are good enough for me. Check out the 54w. Two of them put out 10,000 lumen.

http://www.lightingxp.com/Fluorescent-Fixtures/T5-High-Output-Micro-Linkable/T5-Grounded-High-Output-Linkable-Micro-Fluorescent-c-249-p-605.html

Good MH lamps output 115 lumens per watt. That outshines (sorry about the poor pun!) of 93 lumens per watt of the T5VHO.

The one area that I cannot find any info about is the PAR value of the T5. That is perhaps the most important factor.

Mike

I would tend to think the PUR is the most important when growing plants.

Here's a link to common bulb comparison.

http://www.aquabotanic.com/lightcompare.htm

Keep in mind that the good HIDs use twice to almost five times the power of the T5HO.

taz,

I admit, PUR is new to me but from my understanding, it is more useful for a specific plant (and what cycle the plant is in) as well as the bulb manufacturers being honest about the specific spectrum of the bulb. Obviously, the PUR is always going to be lower than the PAR (LEDs excepted?).

Some people who have studied PUR suggest that its value changes along a tube as well as it is more useful if one is using lower light intensities where a few micromoles significantly change the percentage of PUR/PAR.

Mike

PAR and PUR ratings are invalid and practically useless because

1. They ignore the Emerson Enhancement Effect and other synergistic phenomena. When far red light with wavelengths greater than 700 nm (which is outside the range for PAR or PUR measurement and alone contributes little to photosynthesis) is combined with other wavelengths, there is a substantial synergistic increase in photosynthesis.

See Figure 2 in this paper. As you can see, wavelengths out to at least 740 nm, and possibly even beyond 800 nm are photosynthetically active when combined with shorter wavelengths.

It has long been common practice to supplement regular metal halide (MH) light with incandescent light to take advantage of the Emerson Enhancement Effect. Special MH bulbs such as Philips Ceramic Metal Halide have sufficient far red. In any case, far red content does not affect PAR and PUR ratings.

2. They ignore increased absorption of light caused by a reflective environment. In a perfectly reflective environment, plants will absorb all light of all wavelengths.

>> PAR and PUR ratings are invalid and practically useless Darn, I'm gonna have to purge dozens of bookmarks and correct hundreds of posts relating to PAR actually being something that helps. Might as well toss my PAR meter too, since the data is practically useless. And all the stuff about Moles/Day - maybe it is worth keeping but I think it factors in PAR.

Thanks for en-light-ening me, struwwelpeter!

Mike

But golly, can I enlighten all the guys and girls in the pot and aquarium forums who all this time thought PAR and PUR mattered.

Geez, it's a good thing I read posts in this forum, otherwise I would have believed thousands of scientists and tons of literature that claim PAR is actually a good measure of light and how it affects photosynthesis.

I would have believed thousands of scientists

1. It is inappropriate to take opinion polls on objective matters. Do you believe 2 + 2 = 4 because thousands of mathematicians believe it is true?

2. Name one scientist with credentials who believes that PAR ratings are useful for selecting light bulbs for growing plants.

1) No, I use my fingers and the total seems to be four.

2) A scientist with credentials who relies on ratings to buy lights or a scientist who has opined that the amount of PAR light a plant receives helps the growth process? Big difference.

Tell me, what are you proposing one should use to evaluate lights to be used to grow plants? Lumens? Lumens per Watt? Kelvin temperature? CRI?

Mike