Abstract
In  this  chapter,  secondary  lens  and  optics  solution  for    lighting  will  be presented. Meanwhile, ementary optics  theory will also  introduced  for a better
understanding of lens products. Arrow lighting offer optics solution from suppliers
including  Ledil,  Fraen  as  well  as  asian  sources  such  as  LEDLINK.  These
suppliers  have  custom  and  standard  lens  products  which  fit  for  various
application and different kind of Cree LED products.

Optics Theory in LED
LED contains a lens component, the primary function of LED lens is to extract as
much light from the LED chip as possible and gather the light and shape it into a
beam. For the LED, it has a built-in lens. This lens is limited in its ability to gather
and shape  the  light  into an acceptable beam.  If  this beam angle does not work
for  a  particular  application,  secondary  optics  is  necessary  to  change  the  light
beam into desired specification. 

Fig.1 LED primary optical system and beam angle
 
Therefore, secondary optics  is used  to modify  the output beam of  the LED such
that  the  output  beam  of  the  finished  lamp  will  efficiently  meet  the  desired
photometric specification. Basically, there are 2 main functions in primary optics.
 
a)  Diverging
b)  Collimating
 
a) Diverging,  the  function of diverging  is  to spread  the  lights  into  from a smaller beam  into  a  wider  beam  as  in  figure  2.  Such  optics  solution  mainly  use  in
fluorescent lamp, street lamp and outdoor lighting.   

Fig.2 Diverging lens operation

b) Collimating: the function of collimating is to focus a wider beam into a narrower
beam as in figure 3. Such optics product employed in torch, flashlight and retrofit
lighting application.  

Fig.3 Collimating optics operation
When collimating lights from LED, one can use either reflector or TIR optics (total
internal  reflection)  for  such  purposes.  By  theory,  a  parabolic  reflector  can
generate a beam of light where it is the same size as the exit aperture. However,
some percentage of the light will never touch the reflector and will not incorporate
into  a  beam  shape.  Meanwhile,  the  reflector  surface  is  not  a  perfect  smooth
surface where it create loss to the light beam.
 
Comparing TIR optic products with reflector, it does manage to handle both direct
and reflected light. It is excellent for symmetrical and asymmetrical solutions. 

                     Fig.4 Comparison of TIR and reflector 

PMMA Material in Lens solutions
 
PMMA material  is  widely  used  in  optic  solution,  the  proper  chemical  name  is
Polymethyl  methacrylate  (PMMA)  where  this  material  is  widely  used  as  an
alternative  of  glass. Compare with  glass  in  optics  solution,  it  has  the  following
advantages:
 
a)  PMMA is less dense, only ? of glass density,
b)  PMMA  is typically processed at a  lower  temperature  than glass,  just 240-
250 C.
c)  PMMA is softer and more easily scratched than glass.
d)  PMMA is higher efficiency (over 90% of visible light).
e)  PMMA  transmits UV  light  down  to  300  nm.  Some manufacturers  add  a
coating to PMMA sheets to make them absorb UV light. PMMA molecules
have great UV stability compared to polycarbonate
 
Arrow lighting Optical solution 
 
Arrow  lighting  solution  has  optical  solution  from  different  suppliers  in  various
applications  including  lens  for  street  lighting,  retrofit  as  well  as  reflector  for
portable lighting application. 

Table 1. Arrow lighting Single lens offering 

Table1 is for XRE LED lens products. It contains single lens, lens with holder and
reflector products. For 50x120 part,  it can be used  in street  lamp application as
well as outdoor lighting. 

Table 2. 3 in 1 lens product offering table

Table 3. 6 in 1 lens product offering table 
Table 2 and Table 3 are for lens for multiple LEDs, such as 3 in 1 lens and 6 in 1
lens. Major  application  of  these  len  include  retrofit  lighting  for PAR30, PAR38,
stage lighting and etc. 

Table 4. XPE lens offering table 

Table 5. MCE lens offering table
Table 4 and Table 5  is  for XPE and MCE LED. Since XPE and MCE  is a new
part from Cree. More new solutions coming in from Arrow lighting lens suppliers.
 
References:
 
1)  “FAE training Optics”, Cree Inc, Jan 2008
 
2)  “Innovative Optical Solutions for High Powered LEDs”, Fraen, Mar 2009
 
3)  “Arrow lighting solution guide 2009” Arrow lighting, Jun 2009