I read this somwhere I think but...

[TSPCo]

After several hours playing with the light components, I decided to make my own to play with. I looked at the 2X2 ceiling light and used that as a reference. I have ies files from many different lighting companies (I use them in my day job). I put a spot light in the center on the new fixture, assigned the ies file for it. I decided to check what the fake emitter material was set at, it was 292 Wm^2, how was that derived?
My fixture has .62M^2 of area painted with the material, but the system looks real good and works well, and renders quickly.
If I get this figured out I will donate some light components to the cause, that look real and work like it also.
BTW the fixture I used based on calculations, for 50 foot candles @ a wph of 2.5' took 36 fixtures at 12', for an 80'x40' room.

[Fletch]

The fact that it's a FAKE emitter means you don't need to worry about making any calculations at all. Just set the wattage to something like 250 or 500, something like that. It will render appearing as if it is emitting light in your rendering. Just remember it will not shine any light in the scene unless rendered with Render Setting Easy 09 or 10.

The number is watts per meter squared:
If you have a square light surface you want to have it equivalent to a 200 watt bulb, and the surface area of the rectangle for the light surface is .5 square meters, then you have
(.5m2)(X W/m2)= 200 Watts
(remember that the efficiency power reduction factor is already applied internally for you, so you can just put in the straight wattage number if it's a 1 meter squared light surface... this is done because of the inefficiency of incandescent bulbs to convert watts to light is poor.)
So... to perform the calculation:
(.5)(X) = 200 Watts
X = 200/(.5) = 400 Watts per meter squared *edited*

Performing the calculation is explained in this Tip/Trick thread with an unintentionally deceptive title.
Subject: Lighting Made Simple

[TSPCo]

X = 200/(.5) = 100 Watts per meter squared.

You might want check this, I am sure you meant 200 X .5= 100.
As written, the output becomes 400 watts.

[Fletch]

Correct, 400, not 100.
It should be 400.
This makes sense because if you want the same light output as 200 watts would give from a 1m2 surface, but you have half the surface, you must double the output.
So half a meter squared would mean double of 200 watts = 400 watts per meter squared.
If the light were 1/4 of a meter squared it would need 4x the wattage for the same light output = 800 watts per meter squared, etc.

[derei]

Wouldn't be simpler for V2 to make this calculations internally ? And the user to input the absolute value, not in W/ m squared ?

[Chris]

Wouldn't be simpler for V2 to make this calculations internally ? And the user to input the absolute value, not in W/ m squared ?

That would only work for a very narrow set of circumstances, basically a light component using emitter materials that aren't used any where else in the scene. As soon as you start using the same light emitting material elsewhere, the render engine will spread the emitted "power" across all the surfaces painted with that material to produce the "absolute value". Within that constraint (that it is used only for components with unique materials) however, yes it could done.