6500k bulb brighter than 10,000k???

[Carey1465]

I received my 10k bulb in the mail a couple days ago and put it on my refugium. I did have a 6500k on there but it seems I didnt have no luck with my chaeto growing. I was shocked when I plugged the 10k bulb in because it wasn't as bright as the 6500k but the 10k has more of a blue tint to it. Is this normal? I figured the 10k would be brighter.

[James77]

The more blue and higher kelvin the bulb, in general, the less output and brightness it will have. Bulb-ballast combo will have a role in that, and cetain bulbs will stomp all over others.....but what you see is not unusual.

[Mmiller40gt]

All thing equal yes the 6500 is far brighter. It also promotes more algae growth

[sirreal63]

Originally Posted by Mmiller40gt

It also promotes more algae growth

How so? You can grow algae under 20K bulbs as easily as a 6500, if the nutrients are there, it will grow. Before 20K bulbs were prevalent many many people had algae free tanks with the 6500 Iwasaki, how did they do that?

[Danny_B]

the Kelvin rating has no effects of how bright a bulb is...its only color. a 6500k will grow algae better because it has more red yellow light algae can use, versus a 20000k with very little red/yellow spectrum....which is why you don't see 20000k used In refuge...IMO 2700k-6500 are the best fuge bulbs.

[sirreal63]

It also has more par, a lot more, hence more energy for growth. I prefer the 5500k CF for growing chaeto but the 10k will work.

[James77]

Originally Posted by Danny_B

the Kelvin rating has no effects of how bright a bulb is...its only color.

It is a lot more than just color......most every higher kelvin bulb has less PAR than lower kelvin bulbs. Take a look at Sanjays test results to prove that one.

Compare a 250 watt XM 10K bulb with a 250 watt XM 20K bulb.....If it is just color why does the 10K bulb have far more PAR than the 20k bulb? Same brand, same wattage......

[Bluewater04]

Also our eyes see yellow better than any color so if the bulb is of lower kelvin it is going to appear brighter as well. But yes normally the lower kelvin bulbs do have more par.

[Danny_B]

Originally Posted by James77

It is a lot more than just color......most every higher kelvin bulb has less PAR than lower kelvin bulbs. Take a look at Sanjays test results to prove that one.

Compare a 250 watt XM 10K bulb with a 250 watt XM 20K bulb.....If it is just color why does the 10K bulb have far more PAR than the 20k bulb? Same brand, same wattage......

Just because a bulb of one kelvin rating has more PAR than that of another kelvin rating, this is due to how PAR meters read PAR. It is higher in PAR however, PAR meters dont read all of the blue color, the same is true of out eyes seeing yellow light much brighter than blue light.

It is a because of the spectrum shift. The kelvin rating is based on color only.

[sirreal63]

It depends on the par meter as to how effective it is. The one Sanjay uses reads correctly and Apogee has ones that do as well, but they are a bit pricey for hobbyists.

[garcastle2]

Originally Posted by Bluewater04

Also our eyes see yellow better than any color so if the bulb is of lower kelvin it is going to appear brighter as well. But yes normally the lower kelvin bulbs do have more par.

Exactly. Since the lower kelvin means more yellow, it appears brighter to your eyes. If you look at a spectral analysis of a 6.5k and a 10+k bulb, you would quickly see the difference in light that our eyes see well. I miss the ability to bring my lighting to work and test it myself.