actinic good for plants?
- Thread starter nvision
- Start date
ok you guys have convinced me. i have no time to play god with mix-n-match coloring. i'm getting a new bulb. 
thanks everyone.
thanks everyone.
I'm glad you decided on a new light. It's late to post this, but I had a 50/50 Compact Flourescent and it made my aquarium look "washed out"... The tank seemed to have 'lost' rich coloration. I've heard some really like the look, but it's not for me. 50/50 lights do work well in Saltwater tanks. I have seen this. 
Logic would seem to dictate so, but this is not the case at all. Quite the opposite, actually. A high CRI means that the human eye (which is sensitive to spectra on the photopic curve) sees things as they should be in the daylight noonday sun. Plants "see" with the photosynthetic action spectrum so a high CRI does not necessarily indicate a good plant bulb. If you look at these tabulated results:
Bulb specifications
You'll see that high CRI bulbs such as the Philips TL950 5000K fluorescent very high CRI (98) F32T8/TL950 bulb had a very low PUR (photosynthetic useable radiation).
Basically even though to our eye it might appear brighter, than say, the Sylvania Gro-Lux, the useful output for plants is nearly one third that of the Gro-Lux!
Don't confuse the issue still more by confusing CRI - which is how true colors appear under a given spectrum compared to natural sunlight, with perceived brightness - which should be lumens. These are measuring quite different things, one is color rendition, the other brightness.
That is precisely how I defined CRI: As a measure that indicates that the human eye sees things as they should be under ideal sunlit conditions.
Lumens, on the other hand, provides us very little information when choosing a plant bulb. Lumens are an indication of percieved luminosity, or intensity, based on the photopic curve. The photopic curve is a weighted balance of what our eyes see, as humans.
It just so happens that the photopic curve that lux is based on is just about the opposite of the photosynthetic curve that plants are most sensitive to. Taking a look at that table, many high lumens bulbs had very low useful output in the photosynthetic spectrum. Similarly, many seemingly low intensity bulbs, such as the Gro-Lux with only 1200 lumens, had some of the most intense PUR output.
There are indeed many indicators of bulbs which provide strong output for plant growth, but most of these are misconceptions. I had been under the misconception that lumens was the most important specification to consider. Now I can see that this myth is misleading.
Lumens, on the other hand, provides us very little information when choosing a plant bulb. Lumens are an indication of percieved luminosity, or intensity, based on the photopic curve. The photopic curve is a weighted balance of what our eyes see, as humans.
It just so happens that the photopic curve that lux is based on is just about the opposite of the photosynthetic curve that plants are most sensitive to. Taking a look at that table, many high lumens bulbs had very low useful output in the photosynthetic spectrum. Similarly, many seemingly low intensity bulbs, such as the Gro-Lux with only 1200 lumens, had some of the most intense PUR output.
There are indeed many indicators of bulbs which provide strong output for plant growth, but most of these are misconceptions. I had been under the misconception that lumens was the most important specification to consider. Now I can see that this myth is misleading.
