LENI values have been around for approximately 10 years now, nevertheless with an increasing number of planning specifications today requiring the computation of LENI ideals, they are starting to become essential for most good lighting layouts. In this guidebook, we shall attempt to clarify tips on how to compute it yourself using both the easy and procedures that are detailed and exactly what the LENI is, the variables that go into calculating the worth.

As we would like to assist you still require some help with you and if all that fails LENI computations please do contact us.

What is LENI (Lights Power Numeric Index)?

The LENI (Lighting Vitality Numeric Indicator) approach has an alternate means of computing the lighting energy performance of a structure. Whereas each luminaire is normally assessed for its power efficiency (for example a luminaire without controls should have a minimum efficiency of 60 luminaire lumens per circuit watt), the LENI system calculates the specific power used in KWh per square meter annually. This figure is then assessed against an optimum standard value with regards to the illuminance (lux) demanded inside an area.

Having of demonstrating the conformity of the lighting techniques, an alternate method provides engineers with significantly greater flexibility in their own design, allowing to get a broader collection of techniques light types, and controls to be properly used.

How to Compute the LENI Value?

You can find just two chief types of computing the LENI worth of a space. The primary is the simple approach set out within the 2013 Non-Domestic Building Services Compliance Guide. The second is the more thorough and precise process set out within the BSI British Standard BS EN 15193:2007 Energy Performance of Buildings – Energy Requirements for Lighting.

For the many exact outcomes, whichever approach you choose to use, the LENI calculations needs to be completed on a per space basis (as different bedrooms including offices and circulation areas will likely own very different luminaire types and control systems).

No real matter what procedure you would like to make use of, there are some variants which can be typical to equally you will have to know before undertaking the calculations. These are defined below:

Absolute Installed Lights Power (Pn) – The total strength in t for all of the luminaires within a room/place.

Complete Installed Control Parasitic Energy (Ppc) – The absolute strength in watts of all of the control techniques inside a room/place when the lights will not be in use.

Total Installed Crisis Lights Getting Power (Pem) – The complete charging power in watts of all emergency luminaires in a space/area.

Regular Year Period (ty) – Moment in hours in one year, obtained as 8760 hrs.

Sunlight Operating Hours (td) – Operating Hours of the lighting when daylight exists.

Low-Sunlight Using Hours (tenn.) – Operating Hrs of the lights when day isn't present.

Emergency Lighting Getting Hours (te) – The amount of hours during which the emergency light batteries are billed.

The control variables that were following are used within both Comprehensive calculation techniques and the Simple, however their beliefs may shift determined by the procedure used. To find out your sunlight and persistent illuminance factors please see both the 2013 Low-National Constructing Solutions Compliance Guide for the baloney DURANTE 15193:2007 or the easy system standard for the comprehensive procedure that is.

Occupancy Variable (Fo) – When occupancy controls, the variable that is related to the lighting power are in spot. With respect to the kind of occupancy control this value will fluctuate between ONE and 0, if there is no occupancy control the variable is taken as 1.

Daylight Variable (Fd) – The variable that relates to the lights energy when daylight controls have been in place. Depending on the type of sunlight manage and number of daylight received if there are not any sunlight controls the variable is taken as 1 this can differ between 1 and 0.

Continuous Illuminance Variable (Hamilton Academical) – When constant illuminance control, the factor that relates to the lights strength is in spot. Determined by the servicing aspect of the luminaires this worth can vary between 0 and ONE, if there is absolutely no constant illuminance handle the variable is taken as 1.

The Straightforward Strategy

As previously mentioned previously, the procedure that was straightforward is taken in the 2013 Non-Domestic Building Services Compliance consists and manual of the following equations.

First compute the overall parasitic energy use (If controls are used the parasitic power value might be assumed to be 0.3 W/m2).

Ep=0.3 × Area × ty

Then figure out the energy use that is daytime.

Ed=(Pn × Fo × Fd × Fc × td)/1000

As well as the evening energy use.

En=(Pn × Fo × Fc × tn)/1000

Finally compute the overall energy per-square metre (which is per year). That is your LENI value.


Along with your LENI value finally computed it can be compared by you against the recommended maximum values inside the Low-National Creating Services Compliance Guide to eventually discover in case your lighting layout will honor.


The Comprehensive Strategy

The comprehensive method is required from your BSI English Regular baloney EN 15193:2007 Energy Performance of Properties – Energy Demands for Lights. The computations for calculating the energy use that is closing is pretty like the straightforward procedure, the way these are calculated and the biggest big difference with the thorough approach is the beliefs for the control factors.

First calculate the lights electricity that's utilized to illuminate the building.

Wl=(Pn × Fc)  × [(td × Fo × Fd)+(tn × Fo)]┤┤/1000

Then figure out the parasitic energy needed for emergency lights charging and the control-systems.

Wp=(Ppc × [ty-(td+tn)]+(Pem × te)┤)/1000

Eventually compute the total vitality per square metre per (which can be per yr). This is your LENI value.


The LENI worth can then be compared within the English Standard contrary to the Standard Ideals.


How exactly we might aid?

We’ve strove to clarify LENI computations in the simplest to comprehend way possible, nevertheless we are aware that equations such as for instance these above might not be everyone’s thought of a good time. Where we might aid that is. At Ecodraw Sustainability Consultants and Energy Assessors we love nothing more than carrying out complex computations, so in case you require the LENI values to your illumination design please con Tact us today.