MDI LLF Calculator


The MDI LLF Calculator provides a simple form for calculating Light Loss Factor (LLF) values and storing the specified data in a file.

The available actions are presented in the menu line of command buttons across the top. Calculate uses the current form data to calculate the corresponding LLF values. New or existing files can be opened or saved using the corresponding command buttons. Save will also calculate the LLF values.

LLF Overview

Light Loss Factor (LLF) is a numerical representation of the relative performance of a lighting system in a specific situation described by the different factors included in that LLF calculation. The relative performance is in comparison to the ideal design conditions, and typicallly is reduced (< 1) but may be augmented (>1) in special situations. For brand new systems, performance may vary from the design conditions due to one or more factors e.g. voltage, ballast, tilt or thermal effects. For a lighting system that has been in use, typical factors to be included are lamp lumen depreciation, luminaire dirt depreciation and surface depreciation factors for the room and luminaire. In some situations, particular factors that are usually ignored should be included. Each factor commonly cited is discussed briefly below, and an extra category of 'other' is also provided. All factors use a default value of 1.0 and will be multiplied together appropriately in the LLF calculation.

The overall LLF has two types of components: recoverable or non-recoverable. This distinction is based on the way the factor can be revised by maintenance. Recoverable factors are those that can be changed - hopefully improved significantly - by regular anticipated maintenance, such as lamp replacement or room painting. Non-recoverable factors are associated with those aspects that are not expected to be changed by maintenance, such as ballast factor or thermal effects.

Since LLF values represent system performance at a specific situation, there are differences between the Light Loss Factor for initial conditions - when the system equipment is all new - compared to maintained conditions - when everything is used and probably dirty. The LLF Calculator does separate calculations for initial and maintained conditions. However, maintained conditions can also vary significantly e.g. for group relamp vs for spot relamp strategies. In all cases the user is entirely responsible for understanding the relationship between the values used in the LLF calculation and the corresponding lighting system conditions.

Recoverable Factors

  • Lamp Lumen Depreciation (LLD) Factor
    The lumen output of the lamp decreases over the life of a lamp. The lamp lumen depreciation factor is the fraction of initial lumens at a specific time during the life of the lamp. Typically the time is set to the last moment before lamp replacement.
    Luminaire Dirt Depreciation (LDD) Factor
    Dirt accumulation on the surfaces of lamps, lenses, and reflectors reduces the light output of that equipment. The factor relates to three aspects: the type of luminaire used, the amount and type of dirt in the environment and the expected cleaning cycle for the equipment. The luminaire type influences the degree to which dirt degrades luminaire performance. Indirect lighting systems are likely to lose more performance due to dirt accumulating on optical surfaces compared to direct lighting systems. Typically indirect systems have a lower value for luminaire dirt depreciation. The environment can very from a clean office environment compared to a dirty manufacturing facility. The second and third items determine how dirty the luminaire gets before regular cleaning.
    Lamp Burnout (LBO) Factor
    For group relamping, lamps might not be replaced immediately upon burnout. In such cases a lamp burnout factor can be included in the LLF to account for the reduced system performance. This factor is the ratio of the number of lamps that are burning in the specified situation to the total number of lamps in the system.
    Room Surface Dirt Depreciation (RSDD) Factor
    The amount of light reflected in the room is reduced by accumulation of dirt on the room surfaces. Several characteristics of the room contribute to the factors, such as the type of lighting equipment used, the room's proportions and of course the amount of dirt in the environment. For example, room surface depreciation has a greater impact on the performance of indirect lighting system, since such systems rely on surface reflectances more than direct lighting systems do.

  • Non-recoverable Factors

  • Ballast Factor (BF)
    The device that conditions the electricity for the operation of a gaseous discharge lamp (fluorescent, high intensity discharge, and low pressure) is a ballast. Each ballast differs from the reference ballast that was used to determine the rated lumen output for that specific type of lamp. For fluorescent lamps, the Ballast Factor adjusts the lamp output from the rated value to the actual value under initial conditions. A typical value of BF for magnetic ballast would be 0.90 to 0.95, while BF for electronic ballasts can vary from 0.70 to as high as 1.2 or more.
    Ballast Lamp Photometer (BL) Factor
    Each luminaire photometric test has a particular combination of lamp and ballast. Temperature effects within the luminaire may cause the lampt to operate at less than rated output during the test, which would carry over into all photometric data. When a different combination of lamp and ballast is used in a lighting installation, the temperature effects may change as well. The Ballast Lamp Photometric factor adjusts for such change.
    Equipment Operating (EO) Factor
    The performance of HID lamps can vary due to the characteristics of the ballast, the operating position of the lamp and the effect of radiation reflected by the luminaire or reflector back onto the lamp arc tube. The equipment operating factor represents the combined performance variation due to these aspects.
    Heat Extraction Thermal (HET) Factor
    Some fluorescent luminaires have air-handling capabilities, linked to the HVAC system to introduce or remove air from the conditioned space. The resulting flow of air through the luminaire may change lamp temperature and lamp output. The heat extraction thermal factor represents the remaining fractional performance considering the airflow. This factor may have value greater than 1.
    Lamp Position - Tilt (LPT) Factor
    Some HID lamps' lumen output varies depending on the lamp orientation, particularly metal halide lamps. Lumen output is decreased when such lamps are tilted from the horizontal or vertical design position. The reduction can be significant when metal halide luminaires are aimed e.g. for sports lighting. The factor is defined as the ratio of luminous flux when operating in the aimed position to the luminous flux in the test position.
    Luminaire Ambient Temperature (LAT) Factor
    The output of some types of lamps is significantly effected by ambient temperature. Temperatures variations such as cold exteriors or overheated interiors have minimal effect on any incandescent or high intensity discharge (HID) lamps. However, the light output of fluorescent lamps can be changed considerably due to ambient temperature. This factor may have value greater than 1.
    Luminaire Surface Depreciation (LSD) Factor
    Degradation in metal, paint and plastic surfacees and components results in decreased reflectivity for luminaire surfaces and permanently reduced light output. Some materials, such as glass, porcelain or processed aluminum, have minimal degradation and can be restored to original reflectivity.
    Voltage-To-Luminaire (VTL) Factor
    Variation in voltage provided to the luminaire may affect the lamp output. When the voltage supplied is high, the lumen output of most lamps increases compared to their rated output. More typically, voltage supplied to the luminaire is lower than the rated value, reducing lumen output. The magnitude of change in lumen output with voltage change is specific to each type of light source. Incandescent lamps are particularly sensitive to the supplied voltage.

  • other Factor
    This factor is provided for alternative LLF elements that may not correspond to the listed ones.

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