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Cree Product Characterization Tool (PCT)

For identifying the best LEDs for your lighting-system design

The Cree Product Characterization Tool (PCT) allows you to select from multiple lighting-system design parameters to compare up to three LED models simultaneously.

For all valid LED drive currents, the PCT quickly and easily does the following:

Shows all critical LED design parameters, such as luminous flux and efficacy, for selected LED models
Performs de-rating calculations based on junction temperature (Tj)
Calculates LED valuations, such as lumens per dollar (lm/$)
Estimates simple LED design parameters, such as the number of LEDs required and total power consumption

The PCT uses specifications and characteristics from LED data sheets to accurately compare LED parameters with changes in flux, price and junction temperature. The PCT can compare up to three LED models side-by-side to aid in making critical design choices.

The overall layout of the PCT is shown below. The PCT provides three LED models, each displaying the same four design calculations as a function of forward current in the bottom half of the screen. The top half of the screen contains controls for which four design parameters to display, the range of currents to display, and the system parameters for your lighting design.

LED Models

At the core of the Product Characterization Tool (PCT) is the LED model. The LED model simply defines which LED is being characterized, based on LED type, color and LED connection configuration (applicable to multiple LED products such as Cree’s XLamp MC-E LED).

NOTE: The color of LED is listed in curly braces “{ }” and follows the manufacturer’s naming convention.

LED Model is selected via the drop-down box in the middle of the window, as shown below.

Model Options

The key LED model options are:

Flux. All available luminous flux bins are listed, as well as advertised typical values (if provided)
Price. Price per LED is used for certain comparisons.
Junction Temperature (Tj). Can be defined directly or indirectly by specifying the solder-point temperature (Tsp).

The key LED parameters are entered underneath each LED model, as shown below.

Note: Changes to junction temperature, whether specified directly or indirectly through solder-point temperature, will directly affect the LED VF (forward voltage) and LED LM (luminous flux) parameters, as well as having an indirect effect on every other calculated parameter.

Note: If the Price field is 0 (which is the default value), then the Price values (LM/$, $/LM, c/LM) will be blank.

Design Parameters

After selecting the LED models and entering key criteria, the lower half of the screen will display the calculated values for the four design parameters selected. Design parameters can be changed via the drop-down boxes at the top of the screen, as shown below.

The available design parameters are described as follows:

Category	Design Parameter	Unit	Explanation (all parameters vary by current)
LED Parameters	LED VF	V	Forward voltage of LED
	LED W	W	Power consumption of LED
	LED LM	lm	Luminous flux of LED
	LED LM/W	lm/W	Efficacy (lumens per Watt) of LED
Price Parameters (values will be blank if Price = $0)	LM/$	lm/$	Lumens per dollar of LED
	$/LM	$/lm	Dollars per lumen of LED
	c/LM	¢/lm	Cents per lumen of LED
System Design Parameters	SYS LM PER	lm	Luminous flux of each LED in system design. Note: SYS LM PER is affected by System Optical Efficiency while LED LM is not.
	SYS # LED		Number of LEDs needed to achieve the specified System Target Lumens.
	SYS W	W	Power consumption of entire LED system. Note: SYS W is affected by System Electrical Efficiency
	SYS LM TOT	lm	Luminous flux of LED system
	SYS LM/W	lm/W	Efficacy (lumens per Watt) of LED system.
	SYS $	$	Total price of LEDs in the target LED system.

Current Range

The minimum and maximum values for the independent variable Current Range can be selected via the drop-down boxes near the top of the PCT, as shown below. The step value of 0.05 A is preset and cannot be changed.

System Parameters

The most powerful feature of the Product Characterization Tool (PCT) is the ability to perform quick LED system design calculations. PCT system design assumes the target lumens from the fixture are known and uses the following system design parameters:

Target Lumens. Luminous flux target for the entire LED fixture.
Optical Efficiency. Total efficiency of all optical elements used in the system, such as secondary optics, reflectors, diffusers and baffles.
Electrical Efficiency. Total efficiency of the LED driver from the primary power source, such as “wall-plug” power or a battery.

The system-design values are entered in the top section of the PCT as shown below.

Based on the LED model selected and LED parameters chosen, the PCT can display critical system-design calculations, such as the number of LEDs required and total power consumption for the complete range of valid drive currents of an LED.