Cold Cathode Brightness

Thread Starter


Joined May 11, 2007
Hello all,

I have a question, and this looks like the best place to be.

I rigged a cold cathode light to my aquarium (blue) to create a moonlight.

I got the idea from this website:

(Sorry if linking breaks the rules)

So, I tried it out, using the following types of DC adapters:

12V 1A = way too bright
15V 600mA = way too bright
6V 600mA = almost there, but a bit too dim
4.8V 450mA = way too dim

So, the question is: Which is more important for increasing brightness, voltage or amperage?

I am thinking that voltage plays a bigger part, and if I buy a 9V 500mA, it will be good....what do you think?

Thanks in advance for the help.


Joined Apr 2, 2007
according to me, the current ratings are the max current that adapter can output under short circuit condition.
your ckt will draw current based on the voltage applied to it.


Joined May 16, 2005
Ohm's Law says Voltage = impedence times current. Using algebra, current equals Voltage divided by impedence.

Based on the chart in the article and on your own experience, I suggest either a 9V wall-wart capable of sourcing not less than 600mA.


Joined Aug 8, 2005
Isn't it interesting, that the very DIY article you reference says the following:

"...decided to go with the 9V, 1A adaptor because the light output was pretty close to what I was looking for, and I was tired of cutting up AC adaptors at that point."

Thread Starter


Joined May 11, 2007

Yeah, I saw that, the problem is, I don't have one at my disposal, I can get a 9V, but it will be 500mA....I can get 1000mA, but I have to choose 6V, 12v (I already know is not good) or 15V (have a feeling it won't be good), hence the question....


Joined Apr 27, 2007
I would sugest the use of a LM7809. Those are shortable. So, you would use a 12V adapter, a 0.33microF (25V or more) capacitor between the input and groud terminal and a 0.1microF (16V or more) capacitor between the output and ground terminal.

Refer to:

Also, you should check you adapter for ripple. If ripple is a problem, you may need to replace the 0.33microF capacitor by a bigger one (more than 100microF electrolytic, 25V nominal or more).


Joined Jan 22, 2004
i concur to the suggestion of "mrmeval" for PWM however it would depend on your capability to implement such a project. if you opt for a pot and LM317, i suggest you only get the T-220 package not the TO-3

the suggestion of "cumesoftware" is also good, it simplifies everything.

almost forgot, use a 12v 1A for both suggestions:)


Thread Starter


Joined May 11, 2007
Thanks for all the help everybody.


I couldn't go with any of the more difficult projects because I have no electrical skill, however, I wanted to test the theroy.

So I got a 6V 1A and 9V 500mA and compared them to all the others.

My conclusion is that voltage plays a bigger role than amperage. Of course, if I wanted to splice two more tubes onto the circuit, I may see a difference.

12V 1A = way too bright
15V 600mA = way too bright
6V 600mA = almost there, but a bit too dim
4.8V 450mA = way too dim
6V 1A = almost there (not much different than 6V 600mA)
9V 500mA = if anythig a bit too bright, but I will stick with it (until I fall across a 7V or 8V to try..)