Thinking of getting a light meter, any experiences or advice?

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I was thinking of getting a light meter, maybe this one:

http://www.jlaquatics.com/phpstore/s...uct_ID=mil-lux

The main reason I want a light meter is to help me judge when to replace bulbs for my FW plant tanks and my reef tank. My reef tank is lit by T5's and my plant tanks are lit by CF bulbs.

I don't like the rule-of-thumb that you should change your bulbs every X number of months. First of all it is not based on science or logic but just hearsay. Second every bulb is different and light output will degrade differently from one bulb to the next.

Thus upside of getting a light meter seems to be:

1. Save money on bulbs if it turns out I don't really need a bulb change
2. It would be nice to use the meter to compare different types of lighting, and take it into the store to check out LED lighting measurements for when I get one of these in the future.

The downside to the meter meter that I have thought of includes:

1. No way to calibrate the meter against any known standard
2. Lack of correlation of lux light output vs. actual effect on corals and plants
3. Another expensive reef gadget.

Anyway I wonder if anyone had used a light meter and what their experiences are.