LED lens design principles(previous)

Views: Date：2012/6/11

LED lens design principles(previous)

1.Conceptual design of the optics including estimation of the efficiency
2.Calculation the Etendue of the optical system
3.Selection of LED type and amount
4.Set up of LED models for use in optics design tools
5.Considering the manufacturing issues
6.Development of the optics
7.Tolerance analysis

A. Concepts for LED optics:
1.Plastic lens optics:
-one part with up to 3 or more optical surfaces
→high degree of freedom
-no additional surface treatment
-part costs dependent on thickness of the material
2.Plastic light guides
3.Plastic reflector optics:
-Thin material→low costs for injection molding
-Metallization of surface is necessary→costs increase
4. The use of LED optics provides a high degree of  conceptual freedom with lots of further influencing factors:
-thermal issues, geometrical set up of complete system,etc.
5. Due to the rapid development of new LEDs,the concepts have to be reconsidered from time to time.

B. Etendue calculation:
1.Compared to a lot of standard light sources,the luminance of LEDs is (mostly) a factor 3~10 lower
2.Therefore,especially for optical systems with a low Etendue i.e.head lamps,surgical lights,light guides,etc.
3.if E(led)>E(optic) →light loss

C. Selection of LEDs
1.LEDs are designed for very different features:
-Luminous flux output
-Optical efficiency
-Color rendering index→CRI>93
-High gradient LED
-Multi Chip LEDs to adjust colors or color temperatures

D. LED measurement and modeling for optics simulation
1.To achieve good results from the optics simulation,it is necessary to do a precise modeling of the optical components
2.For LEDs the information of the geometrical (→emission position and direction) and the spectral behavior is needed for the simulation model
3.Ray sets which can be calculated from measurements on LEDs contain this information

E. LED measurement and modeling
1.Measurement of the luminance distribution from more than 10000 viewing directions
2. Calculation of the rays for optics simulation from the measured luminance pictures
Preparing the rays for use in different simulation tools

F. Example: LED sensor optics
1.System Description (Lambert emitting LED; target volume; aperture; optics; aperture in front of LED).
2.Simulation result with ideally lambert emitting light source.
3.Result with realistic light source model.

G. Colorimetric LED measurement and modeling
1.Near field goniometric  measurement of a white LED.
2.Performance of the measurement at different wavelengths.
3.Out of every measurement at the different wavelengths a separate ray set is calculated.