New Bulb Shows Lower Light?

[Arson]

I purchased a new bulb for my planted aquarium today. The stock bulb that came with the fixture I had was a 17W 24" 8,000K bulb. I purchased today a 20W 24" T8 18k bulb. To my surprise when I installed it and turned it on it was a good deal more dim than the previous light.

Now, I don't really know much about lighting and spectrums and lumens and whatnot, but surely it should be brighter. I noticed when I first turned it on for the first 3 minutes or so I could see waves of the gas inside. It settled after a time and appeared to be a bit brighter.

My question: Could it be that this fixture isn't able to support a higher wattage light, is this light just bad, or what? Perhaps the light needs to burn for a good hour or so before reaching its full potential. I'm unsure. Halp!

 

[chrisbassist]

Dint forget about the visible spectrum of light. If some of the output falls outside of this, it will look dimmer to us, but may well be puttingnout more.

 

[SuperColey1]

It may look dimmer, it may have less Lumens but it will be pretty much the same amount of actual light to the plants.

Your unit will support the higher wattage BUT it may still only give the same output in terms of wattage.

I would guess the ballast is an 18W ballast which meant it was only using 17W before BUT it will now only be using 18W. It will never use 20W so you are now using a 20W that is only giving 18W of light.

The reason it looks dimmer is because 8000K is just about perfect for human eye's perception of 'brightness'. Human eye see greens best. However this does not mean it is less light even though it seems so.

AC