I will try my avoid scientific terms as mush as possible and I will do my best to make this Guide easy to understand
Introduction to LED
LED Technology is not new, as a matter of fact it is existing more than 50 years!
but what is new is the recent developments to make white LED from the Blue LED which was not existing at the beginning of first red LED .
also the recent developments includes the high efficient and long life time
Type of LED
there are three main types of LED
- Low Power LED – e.g DIP LED (Dual In-line Package LED)
- Mid Power LED – e.g SMD LED (Surface Mounted Device LED)
- High Power LED-e.g COB LED (Chip On Board LED)
Low Power LED-LED DIP
This is the first LED and has been used for more than 50 years, it developed but still used in application when it is needed as indication not for illumination e.g in Traffic signal.
LED DIP for architectural Lighting
LED DIP is limited to be used as indicator not for illumination in architectural lighting as it has low power and relativity large size compared to other type of LED
Very Important Note
Many products available in the market suggest using LED DIP as replacement for conventional analogue lamp , I sugest avoiding using there types as they are not efficient, don’t provide enough Lumen (Light) , large and don’t look nice
Med Power-LED SMD
it much smaller and gives more light than LED DIP, the main application in cove lighting and strip light or diffuse downlight
the most comment strip light is LED SMD 5050 and LED SMD 3528 but there are many other types- the names comes from the size
SMD 5050 has a dimension of 5×5 mm while the name SMD 3528 has 3.5×2.8 mm
The main application of LED SMD Strip light is in the cove light and concealed light in architectural
for ambient light and General light COB is more economical , but for High end application many manufactures use the multiple Single LED and place in a board to have freedom for design of luminaries, at the end it is the choice of the luminaire manufacturer to deide which is better to design a certain luminaire
according to my experience, the COB makes the lamp big and the optics of lighting becomes big too making
- the luminaire bigger than when using group of individual LED High power
- the light is usually for ambient lighting and very difficult to find less than 10 degree as COB LED luminaire
those are general guides ,but at the end as I mentioned earlier it is the final product to be evaluated not the source alone.
other types of LED
Technology is evolving and there are many types but I we mention the most common
Retrofit LED Lamps
retrofit are the easiest way and most economical way to switch to LED and perhaps the most common one is the MR-16 Halogen lamp or what it is called in different market as QR-CBC 51 lamp with a lamp base of GU5.3
the advantage it is economical however the disadvantage
- it has lower life time
- less efficient than high power LED
my recommendation not to use this lamp in new project and consider replacing old luminaire when upgrading the lighting to the new High power LED
LED COG lamp
LED COG (Chip on Glass) are the replacement for incandescent lamp and it is main application on decorative chandelier
OLED has shorter life time at the time writhing this post and is very costly but technology is ruining fast , however the main application I can see as of current technology is mainly for diffuse lighting for decorative or ambient lighting where you need to see the source of light.
it has exceptionally very thin layer and could be promising in future for some application of architectural lighting.
Selecting and Specifying LED
LED characteristics and specification could vary from LED to anther ranging from very poor to excellent characteristics and the most famous LED manufacturers are
1- CREE (USA)
2- NICHIA (Japon),
3- OSRAM (Europe)
4- Philips – Lumileds (Europe)
5- Toyoda Gosei (Japon)
and some other
If you take one of the manufacturer e.g Cree you will find they have made many types more than 100!
each range has its specification and it is changing from year to another but there are general characteristics that help you specify LEDs
- Efficiency -efficacy
- Color temperature
- CRI and color rendering
- SDCM or Macadam ellipse
- Spectral Power Distribution SPD
- Lumen Maintenance
- Failure Rate
- Damage Factor
To evaluate how efficient an LED is we use the term efficacy because it is not % it is lumen/w or amount of light per one watt
efficacy is simply how mush lumen per watt (light) per watt an LED can give ,
the more lumen means more light for each watt
a typical value for 2016 could be higher than 120 Lumen/watt
efficacy could be different for different color of light, usually the color the light the more efficient is.
Correlated Color Temperature CCT for LED defines the color of the light and could range from 1800 to 10000 K
the lower the Temperature means warmer color
CRI and color rendering
The color rendering is the ability of a white light to render the color of objects , the higher the color the better to show the objects.
the current method use a number between 0-100 , the higher the number the better the CRI is
a good LED nowadays can easily have 90 CRI
it should be noted that the Current method of 8 color or 14 color CRI is found not sufficient and not an ideal way to describe quality of color and the IES has proposed in 2015 a new method called IES Method for Evaluating Light Source Color Rendition TM-30-15
it is not yet adopted globally be seems to be mush more useful to the old 8 color method of CRI
it has Fidelity Index (Rf) , Gamut Index (Rg) and Garphs to show the color quality of a light source
SDCM or Macadam ellipse
SDCM (Standard Deviation Color Matching) or Macadam Ellipse is very important criteria
during manufacturing of LED and applying phosphor coating it is very unlikely to get identical color but the color are very close some time you could see the difference between two colors by eyes and some other time is very difficult to see if there is any difference.
the measure that is used is the Macadam Ellipse which Group of color that are seen identical by human eyes even if they are technically different.
when you have SDCM<2 then the difference is not visible to human eye, and since many many manufacturer have this technology then it is very good to spasfiy SDCM<2
but also it should be maintained for long hours and after 50000 should not be more than 3
Spectral Power Distribution SPD
The light has 7 colors that you could see during the rainbow
similarly with any artificial light source it contains different power of colors represented in what is called SPD (Spectral Power Distribution)
As some manufacture try to improve some color to get better CRI like teh CFL you could get many spikes in some color , the less spikes the more natural the light is
a life time of LED is very long but what is more reverent and more useful is how is lumen (light) is maintained by LED after certain time.
the most used method is IES LM80 and TM21 to determine the lumen after 50000Hour
Most LED manufacture mention the LxBy after 50000 and one of the very popular is L70B50 and L80B10
what dose it mean?
L70 after 50000h:
it means that 70% of the initial lumen is maintained
it means than 50% of the LED will have less lumen than the maintained lumen (Lx)
L70B50 after 50000 h:
it means 50% of the LED are maintaining the 70% of initial lumen after 50000 hours
L80B10 after 50000 h:
it means 90% of the LED are maintaining 80% of the initial lumen and 10% is not after 50000 hours
the higher the L and lower the B is good but make sure these values are given after at least 50000 hours as some manufacturer give better number but only after 25000 hours not 50000 hours!
what dose 50000 hours means in years:
Lumen maintenance is different than total failure some manufacturer give this as percentage 10% or less for 50000 hours , the lower the number of course is better .
it simply means how LED could damage sensitive art and this probably only important in museum and gallery where very sensitive art is being exposed to light
LED in general is better that Halogen and HIT but it is very important to ask for the value of damage factor for the LED
good value that was published by ERCO is Damage factor 0.149 mW/lumen which is lower than halogen.
That was specification of LED but what about LED luminaire
An LED luminaire has mush more than LED!
- The LED
- Heat dissipation system
- Control Gear or Driver
- Optical System
- Other Mechanical system for some protection like IP
How to specify those
Heat dissipation system
The Heat-sink is very important as it helps ruining the LED for its lifetime and ensuring maximum efficiency
There are many types- basically heat sink could be passive or active
The active heat sink uses the fan to cool the LED while the passive heat sink use metal like aluminium to cool the LED.
Active Heat Sink with Fan
Personally i prefer the passive as it is very difficult to get the fan run for more than 50000 hours. also if the fan fails the LED would have shorter life time. however there could be some application where you don’t need the 50000h like shops and retail.
Control Gear/LED Driver
LED Driver help supply the LED with the right current.
each Driver has certain capacity in Watt and input as well output
LED runs at different currents depends on manufacturing and heat management, the lower the current usually the more efficient the LED is while the higher the current the more cost effective is.
the most common current to drive LED is
LED Driver has to be selected to match the LED luminaire manufacturer , some manufacturer they supply the complete luminaire with driver some other supply without driver.
to select the right one you should select the right mA, Watt
Type of Drivers
There are many types to control or dim the LED , the most common ones are
2-Phase Dimmable Driver
3-0-10 Volt Dimmable Driver
4-DALI Dimmable Driver
Switchable LED Driver
They only switch LED on/off
is economical solution but limited in controlling the light
LED Phase Dimmable Driver
this could be controlled by the same way as halogen and incandescent lamps
the disadvantage that not compatible with all dimmer in the market you have to make sure that the dimmer is made to dim LED type.
0-10 Volt Dimmable Driver
This is better in terms of compatibly with LED , it is controlling the driver by 2 wires different than the power line unlike the first option
- as the wires diming the LED are different from the Power then no issue with dimming .
- could be easily connected with smart system like KNX.
- has limitation as you have to define the luminaires that will be dimmed together before wiring.
- it uses a lot of lines for each group of luminaires, you need separate wire e.g if there is 5 rooms in each rooms there is 3 group of luminaires to be controlled speratlly then you need 15 pairs of wires for the five rooms.
LED DALI Driver
This is the most flexible driver
the DALI (Digital Addressable Light Interface) driver is smart driver that receive and send information through a wire to the controller
- one wire can connect 64 driver to the controller eg if there is 5 rooms in each 3 groups you only need one pair of wire to the controller.
- High flexibility since you can decide after installation which luminaire should be dimmed , it could be programmed any time by the installer or technician.
- you need only one controller per 64 driver.
- excellent for connection with smart system like KNX
- The driver has more cost compered to the other drivers, but with good design the system could be less expensive as it have less wires and controllers, it really depends on the situation.
Method of Dimming LED
there are two types of dimming LED PWM and CCR
PWM Pulse Width Modulation
in PWM the light is reduced by reducing the with of the plus
the LED color will not be changed
is not suitable for Video conferencing as you could see the light is moving and not stable, Human eye cannot see this frequency but the camera dose
CCR Constant Current Regulation
in this method the light is reduced by reducing the current
the light color could change slightly but it is unlikely noticeable
very good for video recording
I would recommend the CCR since nowadays every almost one is recording video at least with mobile phone!
the optical system of LED control the light
Optical System For mid power LED
it is mostly diffusers
there are many types of accessories to help hold and control the light of LED SMD
Also there many types of diffusers e.g clear, Opal
usually the more uniform the light the less light output the diffuser will get
these channel help installing the LED strips inside architectural details like floor or shelfs
the designer should select the right type and ensure proper coordination with architectural details
Optical System For High power LED
mainly lenses or reflector to control the light of High power LED
To see the application of different beam angle you can see the LdG-2
Lighting design LdG + LdC Page
if you are intersected in learning lighting design software then you can visit this page