What does a light meter tell me?

I got a meter that comes in 3 settings, it measures PH levels, moisture levels, and light levels.
The light meter goes from 0 to 2,000
What is this? Lumens? Kelvins? :S in the sun it's at 2k+, 2k+ directly under my fluors, and like -1k under a regular light.

(The thing cost me 8 bucks from china on ebay but it's accurate on the ph with the strips so I'm hoping it's accurate on the other two)

Measure full sun. Measure your lights. Cry.. buy more light.

The one you got dosnt tell a damn thing. Well anything that means anything. Most meters read lumens. When lumens drop the spectrum is going out.