Aquatic Plant Central - View Single Post - Lighting Spectrum and Photosythesis
View Single Post
Old 03-12-2007, 04:41 PM   #10 (permalink)
Senior Member
Newt's Avatar
Join Date: Mar 2004
Location: between Here and There
Posts: 3,113
iTrader Ratings: 49
iTrader Positive Rating: 100%
Newt is a regular member

Hi Moment,

You have a good thread started there.

I dont think you mean relative power in areas of blue and red. A lot of companies market bulbs with spectral output graphs based on 'relative' power and not a meaningful measurement such as watts per nanometer per 1000 lumens, as other companies do. This is probably because the former companies dont want you to know how little intensity is actually being emitted at a given nanometer. Relative power is only measuring the various outputs to the highest peak which they call 100%.

As for the second post (first to your original): "white light at 5000K looks terrible". This could be a combo of issues: first, the bulb manufacturers basically pick a kelvin rating somewhere near the bulbs actual kelvin temp because they want to market it as a 6500K bulb and not say 7245K, or whatever it may really be. The second issue could the a lower Color Rendering Index of the bulb. I use 5000K Philips PLL-950's (along with other bulbs) and the CRI is 92 which is very high. It is definitely a very white light. But I bet if I were to put it next to say a 5000K MH with a 98 CRI it would look yellow.

As for your resistance to your thread, just look how mine started. Most people are only going to choose based on kelvin ratings and that is too bad. They may have good luck doing that but wont know what they can really accomplish if they tried this approach. I find it curious that the Dutch and other Europeans choose lighting at around 3500K and as high as 5000K with only a few using say 6500K. They use a lot of Philips PLL 840s and 860s as well as some Osram bulbs similar to those. Here in the US hobbistes are going form like 6500K to 10,000K. Part of the issue is alot of bulb manufactures do not provide spectral output graphs and most of the ones who do use the relative power to describe the output intensity. If you choose a bulb that has a high CRI the kelvin doesnt play into it so much. So many people I see are using Coralife 6700K. They have good marketing but the bulb has an dominant spike in the green and casts a green hue on the tank. Perhaps they like this as it makes their plants look very green. Then you have people using the GE 9325K that only has a 67 CRI yet people love them. I used them awhile back and they grow plants well but the red region is more in the orange and not up near 675nm. I don't think they are that close to a 10,000K anyway. I had one side by side a Philips C75 (7500K). The Philips had a blue tone and the GE had a pinkish/red tone. You would think the GE would have looked more blue. I prefer a nice white light.

The GE 9325K:

I hope this has helped.
Newt is offline   Reply With Quote