Define Lighting Requirements

The LED luminaire must meet or exceed the lighting requirements for the target application. Therefore, the lighting requirements must be defined before establishing the design goals. For some applications, there are existing lighting standards that will define the requirements directly. For other applications, a good approach is to characterise an existing luminaire.

Table 2 (below) lists important characteristics to consider when characterising an existing luminaire. The light output and power characteristics are always critical, while other characteristics may or may not be important, depending on the application.

Importance Characteristic Units
Critical Luminous flux lumens (lm)
Illuminance distribution footcandle (fc)
Electrical power consumption watts (W)
Potentially Important Luminaire aesthetics


Operating temperatures


Operating humidity % RH
Colour temperature K
Colour rendering index (CRI)
Ease of installation
Form factor

Table 2 - Important Characteristics of Target Luminaire

All lighting companies can provide data files or documentation that detail the “critical” characteristics for each of their fixtures. The “potentially important” characteristics are more subjective or may not be listed in the manufacturer’s documentation. In this case, it is up to the designer to characterise the existing luminaire.

led lighting
Figure 1 illustrates the critical characteristics for the example CFL downlight.

Part Characteristic Unit Value
Lamp Technology CFL
Light output lm 1,500
Power W 23
Efficacy lm/W 65
Lifetime hrs 10,000
Average selling price US $3
Fixture Coefficient of utilization (CU) % 54
Light output lm 810
Power (excluding ballast) W 23
Efficacy lm/W 35
ASP US $20

Table 3 - Example CFL Downlight Characterisation.

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