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.

Overview of the LENI EN 15193-1 formulas.

Lets look a bit more into the top level formulas of LENI...

 ...and this is part of the numerator of the LENI formula...

...but what do all those terms mean?

The simplest term is Pn, the total installed power for lighting, ignoring emergency lighting and charging of emergency lighting batteries. The n stands for "normal" I presume, as opposed to "emergency" or "charging".

Fc (more on this here) can reduce the weight of Pn because constant illuminance control (CIC) can reduce the power used to illuminate the room. This can happen because sunlight enters the room and electronic controllers react to it and reduce the power driving the luminaires.

Fo is the occupancy factor and takes into account that often lights are switched off when  rooms are not occupied. For example a store cupboard may have 50W of lighting installed, but it is only ever switched on when someone goes into it to get a broom. Say 0.1 or 10% of the time. This would make the actual consumption be calculated at 5W (not 50W).

The terms in square brackets are a way of splitting the calculation into day-time and night-time periods.

td is day-time hours. tn is night-time hours.

td x Fd: is a term which can be thought of as: "how much lighting will I need during the day":

• Fd is 0.0 if there is always enough natural light during the daylight hours. 
• Fd is 1.0 if artificial lighting is always required during daylight hours, for example in a room with no windows, no natural light.
• Fd is somewhere between 0 and 1 if, during the day, you sometimes need to switch a light on, but not always.

tn does not have a factor because you know you need lighting at night-time. And if nobody goes into the room at night-time is handled by Fo, the occupancy factor.

So...

 Fo[(td x Fd) + tn]

...handles the energy consumption change because occupancy of the room, requirement for lighting energy during the day and requirement for lighting energy during the night.

The next entry is on constant illuminance control.