Cymap Lighting – Lumen Calculations when using LED Luminaires.

by David Wren

LED light fittings are becoming more and more commonplace due to their higher luminous efficacy. This makes them a natural first choice for new and upgraded lighting installations.

Consequently, it is important to be able to keep up with present day lighting design requirements and CIBSE SLL codes of practice.

To assist the Building Services & Lighting Design engineers to be able to deliver efficient lighting systems, there have been upgrades specifically for LED luminaires, developed for the Lighting Database program. Coupled with the revised LED lighting calculations, this in turn will enable the design engineer to accurately model LED luminaires in both the Single-Room (CYL) & Multi-Room (CYC) Lighting projects.

In lighting calculations, the MF (Maintenance Factor) for LED luminaires is derived from the LLMF x LSF x LMF x RSMF. Where the LLMF & LSF are taken from manufacturer’s performance tables, using the following User selected data:

• The Service Rating (L90 - L50). - The luminaire’s life efficiency. Service Rating.
• Design Hours (10,000 - 100,000). - The manufacturer’s useful life expectancy of the luminaire. Design Hours.
• The luminaire’s Operational Hours – Calculated from 'Hours on in Year' (Hours per day. Days per Week. Weeks per year). Multiplied by the results of the LED fittings’ Cleaning & Replacement schedule (the intended Operational Hours of the luminaire(s) before it is replaced.)

As illustrated below, using an LED luminaire with a Service Rating of L80, a Design Life of 80,000 hours and an Operational Hours of 15,000 hours, the resultant LLMF is 0.96 and the LSF is 1.00.

This illustration also shows how all the selected and entered data is utilised in the calculations. It demonstrates the relationship of:

• The entered data for the ‘Hours on in Year’, plus the selected ‘Cleaning & Replacement’ schedule.
  Please note, in a Multi-Room CYC project, different values for the ‘Hours on in Year’ can also be set in the ‘Edit-Settings’ dialog. For either a Template Profile, or on an individual Room-by-Room basis. Those hours are then combined with the ‘Cleaning & Replacement’ schedule to calculate the luminaires’ Operational Hours.
• The Results in the ‘Lumen Calc’ for the LLMF & LSF values, plus the LED performance table where these factors came from.

Please note: The LED luminaire Service Rating tables (as shown above in the background for an L80 Service Rated luminaire), are included in the software and are used by the program in the Lumen Calculations.

When adding LED luminaires to a project’s Lighting database, manufacturer’s technical notes should also be consulted for details of the luminaire’s Design Hours and Service Rating, in order for the correct LLMF & LSF factors be used in the Lumen Calculations.

Manufacturer’s data from IES TM-21-11: projecting long term lumen maintenance of LED light sources.

For more information, please perform a Search for ‘LED’ in the Cymap Help program and follow the appropriate link.

Here, you will find guidance on how to add LED fittings to the Lighting Database program, as well as how to set them up to perform a ‘Lumen Calc’ in the Single Room program (CYL) and the Building model (CYC - Multi Room lighting).