same thing? no: lumens is a measure of brightness, contrast ratio is a measure of, er.. contrast.

convert? no.

what are they? in very simple terms, the contrast ratio is about how dark your blacks are, the lumens is about how bright your whites are.

projectors usually have a published contrast ratio too - but this is mainly down to the video processing chip, and only slightly affected by other components, such as a dynamic iris. With each generation of projectors often using the same chip (or alternatives with very similar specs) within any given price range, they tend to have near-enough identical contrast ratios. Consequently this figure doesn't make any model stand out from its direct competitors, so it doesn't get much prominence. e.g. a few years ago many projectors used Texas Instruments' DarkLight chip; the next year DarkLight 2; then DarkLight 3. each generation of chip providing a higher contrast ratio (as well as other improvements)

The lumens value is to give an idea how powerful the lamp is, which is an important consideration particularly when the projector will be mounted a long way from the screen and/or the room has high ambient light levels (e.g. thin or open curtains) Lower lumens means a less bright light, which means the image will be washed-out by less ambient light and/or dimmer if the throw distance is too large (with "too large" being at a shorter distance than for a higher lumens model). Brighter lamps allow clearer images over longer throws and lighter rooms.

Projectors usually have 2 lamp power modes: standard and economy [different manufacturers may use different words, but they normally quote the standard (or full power) value]. Most manufacturers design and sell their own lamp assemblies, so there is more variation in the lumens ratings between makes and models, so it is given more prominence.

With a plasma or lcd screen the throw distance is irrelevant (obvious, hopefully!) and the ambient light wash-out is cured by adjusting the screen and/or viewing angle, turning the brightness up, or closing the curtains.
The contrast ratio with these is (relatively) more affected by the chemical composition and physical engineering of the screen itself, resulting in much more variation in the contrast ratio between different makes and models. This makes it a differentiator in marketing terms, and therefore worthy of more prominence. Flatscreens may also have a Lumens value (presumably achieved by measuring the light given off when showing a pure white image) but as the screen is the light source, it wouldn't be good if the value were anywhere near that of a projector -- there's a reason projectors come with a safety warning along the lines of "do not look directly into the lens when lamp is on!"