Is it possible to find out whether an LED lamp fitting is going to be good/not good for my tank?

I'm looking into upgrading the light on the loach tank from a 11W Jebo type with a short tube that sits over the width rather than the length (like this http://www.trademe.co.nz/pets-animals/fish/lights-lamps/auction-442700057.htm ) to something that runs the length of the tank for a better spread.

It seems that a light to fit a just over 50cm tank is quite hard to find, they seem to come in 45cm long to 60cm long. I want to get something that has feet so it stands over the glass rather than sitting directly on it.

So anyway I found a LEO fitting that has 16 5mm blue LEDs and 42 white ones (the light on this tank http://www.trademe.co.nz/pets-animals/fish/fish-tanks-aquariums/auction-444020384.htm ). It says it is 3.5watts and the colour spectrum is 6000-7500K. My tank is low tech so what I need to find out is whether the LEDs are going to be too much. I don't mind it giving off low light but too much will cause algae I think.

You've already got a 11W lamp, so dropping to a 3.5W lamp sounds like less light than you've got now. LEDs are more efficient than fluorescents so will produce more light for the same wattage. But keep in mind that lamp is designed for a 12L aquarium, and yours is larger?

There are smaller LEO or other LED lamps that say they are suitable for up to a 30cm tank. Mine is about 53cm long and this one has more than double the number of LEDs than the smaller ones.

I understood that though LED uses less electricity the quality of light is better :dunno:

You can target colours better using LEDs. The blue lights will encourage plant and so presumably algae growth so you could turn off the blues if that happened.

I'd say that 3.5W will probably produce more light than the existing 11W, provided the LEDs are decent.

I have a nano marine tank and replaced 20W of halogen with 1.4W of LED. You can see pictures here http://www.fnzas.org.nz/fishroom/viewtopic.php?f=5&t=53458

thanks