Customized LED lenses of various sizes and perfect light effects for CREE OSRAM CITIZEN BRIDGELUX COB LEDs

Roadway Lighting: Purpose, Requirement
• Purpose of Roadway Lighting
– Illuminate roadway, sidewalk, bicycle pathway, signage
– Appropriate lighting reduces incidents of night driving
accidents
• Requirement for Roadway Lighting
– Illuminance Distribution
• Minimum Illuminance
• Uniformity
– High Efficiency
• Less energy loss as the number is high
– Illuminated area
• Illuminate roadway
• Do not illuminate other than roadway
• Expand the space between luminaires to reduce the number
• Optical performance is important for roadway lighting =>Optical designing is important

Roadway Lighting: Superposition & Tiling
• There is a couple of ways to build desired illuminance distribution with multiple LEDs
• Superposition
– All LEDs contribute to illuminance distribution equally
– Does not cause dark space even if one of LEDs is gone out
– Not affected by individual variability
– Need to adequately expand light

Roadway Lighting: Superposition & Tiling
• Tiling
– Each LED illuminates different area
– Causes dark space if one of LEDs is gone out
– Affected by individual variability
– Boundaries of illuminated areas from each LED are noticeable
• Superposition + Tiling
– Still problems of dark space and
individual variability
– Boundaries of illuminated areas are not noticeable

Roadway Lighting: Primary Designing Approach
• Choose one of three approaches below for
primary designing
– No Optical System
• LED themselves are placed at a particular height
– Direct Optical System
• LED (and emission direction), optical system and ground are in line
– Indirect Optical System
• Other than “Direct Optical System”
• Light from LEDs does not directly emit toward ground
• Each Optical System has advantages and
disadvantages for performance and aesthetic

Roadway Lighting: No Optical System
• The best approach if selected LEDs
have the desired intensity distribution– Most high-brightness LEDs have
Lambertian (cosθ) intensity distribution
• Can also work if LED intensity
distribution is narrow and each
illuminated area can be controlled by tilting each LED
– Tilt and place lamps
– Basically same as “Tiling”
• Can see LEDs directly from many
direction
– Causes glare (reduces visibility of objects and visual performance)
• Cannot control light efficiency

Roadway lighting: Direct Optical System
• Can control intensity distribution
– Intensity distribution which only illuminates
particular area is important for “Superposition”
– Intensity distribution is needed to be converted as it is rare that a LED has such intensity
distribution
• Works well with high-brightness LEDs
– Can convert Lambertian intensity distribution
to more suitable intensity distribution
• Can greatly reduce angular region which
LEDs can be directly viewed
• Light efficiency can be higher than “No
Optical System”
– Light can be extended too much with “No
Optical System”
• Optical System is refractive or reflective

Roadway Lighting: Indirect Optical System
• LEDs are not directed
toward to the ground
• Optical system redirects
light from LEDs toward the ground
• Hard to view sources
directly
• Difficult to efficiently
redirect light from
Lambertian LEDs

Roadway Lighting: No Optical System Example
• 27 Cree XR-E LEDs
• No Optical System
• Placed Height: 5m
• Mechanical structures were
designed in SolidWorks
– Imported SolidWorks assembly
into LightTools
– Set optical properties to all of the surfaces
• Roadway and mechanical
structures absorb light
• The lens considers Fresnel Loss– Add sources and receivers to the model
• Each of the sources emits 100lm• Ran optimization to smooth and
spread the illuminance distribution

Roadway Lighting: No Optical System Example (Result)
• Peak Lux on roadway surface: 40Lux– Results for 10 million rays
• Linear shadow appears on the
illuminance distribution by the effect
of refraction through the outer lens

Roadway Lighting: Direct Optical System Example
• A unit of Cree XR-E LED
and a Lens
– LED Flux: 100Lumen
– Placed Height: 5m
– Optimize the lens shape to uniform illuminance on a
7m x 12m area
• LED only
– Flux on the 7m x 12m area: 68Lumen

Roadway Lighting: Direct Optical System Example (Result)
• Flux on the 7m x 12m area: 83Lumen
– Higher Efficiency: 68%=>83%• Superposition is possible
– If more units are placed,
illuminance is increased

Roadway Lighting: Indirect Optical System Example
• A unit of Luxeon K2 LED and a faceted mirror
• Placed Height: 5m
• Module Configuration
– If more units are placed, illuminance is
increased
• Mirror Reflectance: 75%
• Optimize the reflector

Roadway Lighting: Indirect Optical System Example (Result)
• 12 LEDs
– Each LED emits 180Lumen
• Peak Lux on roadway surface: 25Lux• The Reflector shape is not optimum
– Efficiency: 40%

Roadway Lighting: Evaluation of Appearance
• Not only the value of illuminance distribution but also rendering like CG is effective to evaluate appearance– LightTools Photo Realistic Rendering feature
– Possible to export designed intensity distribution in
LightTools as IES file and import it into CG software