LENI Pn x Fc and Fcc constant illuminance control.

Let's look at that formula again:

Fc is the constant illuminance (dependency?) factor, and relates to how light output from a given luminaire decays over time and how constant illuminance controls can compensate for this.

If there is not constant illuminance control then Fc is 1. If there is constant illuminance control... then the situation gets more complicated.

You now need to know about:

1. Fcc, the efficiency of the constant illuminance control
2. Constant Lumen Output, CLO, which adjust power (over time) in the luminaire to keep the output (in lumen) constant as the luminaire degrades.

 Here is how I have explained this part of the EN 15193-1 it to myself:

  The top left quadrant of diagram above uses Fcc. Fcc is/was  bit of a mystery to me and only by asking my Italian colleagues could I begin to understand it. 

From the actual EN 15193-1 standard:

"Fcc = Factor for the efficiency of the constant illuminance control"

The Interweb was no help, so here is my explanation, interpretation, guess.

Efficiency in what sense? It seems that it means efficiency in how it handles the constant illuminance control, i.e. how accurate it is in keeping the flux and illuminance at the required level in various conditions.

In other words a low Fcc system would not change the flux appropriately, and a high Fcc system would change the flux appropriately.

So a better definition, if I have it right, would be: 

"Fcc = Factor for the accuracy of the constant illuminance control"

I'm willing to be corrected by anyone who can point me to a complete explanation of Fcc. 

Luigi Schiavon gave me this explanation:

When we say Fcc = 1, it means that a reduction of 50% of the power to the luminaire would result in a reduction of 50% of the flux of the luminaire. Probably, in reality, it could be that a reduction to 50% of the full flux requires 70% of the power, and Fcc would be calculated at 0.5/0.7 in this example, and so Fcc= 0.714.

It is also very possible that the relationship between flux and power is not linear, so a single number, Fcc, cannot characterize it.

In practice, with all the approximations already used inside the LENI calculation, we can take Fcc=1, because Fcc does not influence the final result very much. Plus obtaining a real value for Fcc for luminaires probably requires heroism above and beyond the call of duty.


And here's a post on how to use AD and AND areas.

And here's a link to a program which calculates LENI for you.