If you haven't read this article yet, I highly encourage it. It is long and requires a bit of understanding of biology and physics, but you'll learn a lot from it.
A Comparison Between Light Sources Used in Planted Aquaria
This came from a discussion I was having with one of our newer members, collapse. He was wondering what impact lumens had on choosing a lighting system for plants. My intial response was that lumens are far more important than color temperature or CRI and should be a prime consideration when choosing a bulb for your planted tank. But then I re-read this article and fell across this passage:
Based on the Photosynthesis Action Spectrum (the wavelengths that plants are more sensitive to), light bulb manufacturers came up with fluorescent "plant bulbs". They basically emit most of their light in the wavelengths that are more efficient for photosynthesis, namely the red and blue ends of the visible spectrum. As expected, these light sources look dim to the human eye and consequently have poor lumen ratings. Also, their color temperature and CRI ratings have little, if any, meaning. After all, these bulbs were not designed to be "seen" by humans.
Obviously, not all humans like the pinkish glow these bulbs emit, but our plants sure do.
The popular GE Plant & Aquarium bulb is only rated at 1900 lumens, yet offers a PUR (photosynthetic useable radiation) of 20.9. A generic 4100K "cool white" bulb has a much higher lumens rating of 3050, but only offers 20.5uE/s of PUR.
Recently I switched to OSRAM/Sylvania's Gro-Lux bulbs (sold at Lowe's) and these bulbs have an even lower
lumens rating at 1200, yet offer a PUR of 27.4!! In the ODNO thread, ridns replaced his 5000K Phillips T8 bulbs with these same bulbs from Lowe's and even though the total lumens output has decreased, his plants started pearling within 10 minutes! The high-CRI Phillips bulb he was using (Philips TL950 5000K CRI (98) F32T8/TL950) had a standard lumens rating of 2000, yet only offered a PUR of 8.9 uE/s
! He was effectively increasing his photosynthetic useable radiation by over three
times even though the apparent brightness of the bulbs decreased.
Ok, so if you're still with me, what am I trying to say? Basically this, don't think you've increased the amount of light your plants can use just because one bulb looks brighter than another.