Understand Led light bulbs technology

Nowadays LED light bulb is the ubiquitous choice when you start shopping for a replacement light bulbs in your home.

What is LED?

LED stands for light-emitting diode, which was invented by a Texas Instrument engineer James Biard. The first visible-spectrum (red) LED was demonstrated by a General Electric engineer Nick Holonyak.The first Blue violet LED using magnesium-doped gallium nitride was made at Stanford University in 1972 by Herb Maruska and Wally Rhines.

In August 1989, Cree introduced the first commercially available blue LED.

Until 1993, high-brightness blue LEDs were demonstrated by Shuji Nakamura of Nichia Corporation.
Nichia Middle Power LED package 3mm*3mm*0.6mm
 

There are two primary ways of producing White light-emitting diodes. One is to use individual LEDs that emit three primary colors—red, green and blue—and then mix all the colors to form white light. The other is to use a yellow phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light. The yellow phosphor is Cerium-doped YAG crystals suspended in the package or coated on the LED. This YAG phosphor causes white LEDs to appear yellow when off. Alternatively, white LEDs may use other phosphors like manganese(IV)-doped potassium fluorosilicate (PFS) or other engineered phosphors. PFS assists in red light generation. Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. 

 
The first white LEDs were expensive and inefficient. However, the light output of LEDs has increased exponentially over the past decade. Commercially available LEDs have an efficiency of up to 223 lm/w as of 2018. 

What is in typical A19 shape size led bulb with a E26 medium screw base?

A19 shape size is 19* 1/8 inch, or 2-3/8 inches at the light globe size. The size chart is very helpful for some the recessed light with an enclosure.
 
E26 medium size is the standard (most common )screw base size of house hold light bulb in USA. The “26”Standard for 26 mm in outer diameter size . Here is a list of all the other typical screw base size. 
Let us get back to the answer of what is in the led light bulb .

It consists of 3 major sections :

section1 , External mechanical housing which includes:
 a: screw base ;
 b: shield optics ;
 c: external housing enclosure.

section 2 , led driver and control circuitry. LED driver get the AC power input and module the voltage and current before supply power to the led light engine. Led driver is the core engine of the led light bulb. A good power supply from the led driver can produce the good quality of light without any visible light flicker, and able to help bulb survive in dirty power condition, such as fluctuating voltage, and electrical transient event ( surges). 
 
 

section 3 , light engine ,which typically has multiple LED modules placed on a PCB . The quality of the led light depends on the LED used. LEDs can determine the energy efficiency of light and color quality of light.

Led bulb is relative energy efficient comparing with other light sources like Incandescent ,Halogen and CFL (compact fluorescent light ). A typical 60w incandescent can be replaced with a 12w LED bulb to deliver the same light output( 800 lumens).

EPA in the Department of Energy has created a program for supporting the adoption of energy efficient lighting bulbs and fixtures- Energy Star program.

You can go to Energy star’s website to select the energy star certified led light bulbs.

The major benefit of energy star certified products are:

Independently certified to deliver efficiency and performance
Same brightness (lumens), 90% less energy (watts)
Last 15 times longer = big $ savings
Help protect the environment and prevent climate change

Step 1, get on the landing page,

Step 2,choose the lightbulb shape match your current bulb

Step 3, choose the color of the light match your current bulb/or your preference:

there are 5 color categories :

1, Amber light (2200K -2500K CCT , The bulbs match the color of filament bulbs and appear very yellowish.)

2, Soft White (2700K is the most commonly used color for indoor applications and provides a familiar, slightly yellowish tint to your surroundings.)

3, Warm White (3000K provides light without a blueish or yellowish tint.)

4, Cool White (3500K to 4100 K CCT ,4000K bulbs provide a whiter hue for a bright appearance.)

5, Daylight (5500K to 6500K CCT, 5000K+ light is similar to daylight and is generally too bluish for most indoor applications.)

Step 4 , choose the brightness( light output in lumens)

step 5 ,here is the result page. it has a summary of the light facts.

Step 6 , energy star certified light bulbs that meet your requirements . At this page, you can use the filter to find the right bulb for you and where to buy it .

I want to explain some of these filters on the website which may be helpful to better select the right led bulb for the application.

First is the Special Features filter. 

1,Dimmable: this means whether bulb is designed with supporting electronics circuitry to support dimming down the light output. Dimmable light can further save energy consumption and also help creating lighting scenes.

 2, Not for use in Enclosed fixtures. For lighting fixture that has a enclosed optic cover ,you should find a led bulb that rated for used in the enclosed fixtures, otherwise misuse light bulb that could overheating the led bulb ,damaged the bulb prematurely.

 3, Not for use in recessed fixtures: recessed fixtures are typically Insulation Contact rated housing that will create a higher operating ambient temperature for the light bulb. so you should find the bulb rated for recessed fixtures.

4, Wet location/ Damp Location rated. Wet location are locations like bathroom, kitchen ,exterior wall ,porch light. Damp location is the general hall way ,living room common areas.

5, Use with photo and motion sensors, if the light bulb not listed for this sensor application, what could happens is premature light failure due to electronics physical failure. every light bulb has life expectance with a normal turn on/off frequency, so lifetime of bulb is calculated based on 1on/off cycle per day, not a 10 times on/off cycles as a sensor enabled light bulb.

the electronics designed for the light bulb supporting sensor will need a robust design to support the multiple (such as 5) years warranty.

6 , shatter resistant feature is good to prevent the bulb optics shield spreading when the bulb is broken .

 
What makes a good quality led light ?

Key aspects of high-quality light are the color appearance of the light itself, which is described by its color coordinates but is often condensed to Correlated Color Temperature (CCT), and how the light affects the color appearance of objects, which is referred to as color fidelity. Color fidelity can be quantified using the Color Rendering Index (CRI), or with another color metric, the recently developed TM-30.

In general, a minimum CRI of 80 is recommended for interior lighting, and LED products can readily meet this standard. CRI of 90 or higher indicates excellent color fidelity; LEDs can also meet this threshold but at a relatively higher price point.

CRI is far from a perfect metric and is especially poor at predicting the fidelity of saturated reds, for which the supplemental value R9 is often used. The fidelity index (Rf) and the gamut index (Rg), which are described in IES TM-30-18, can provide a more comprehensive evaluation of color rendering.

What about the flicker ?

AC lighting including incandescent, CFL and LED types generally exhibit varying degrees of flicker; usually at double the AC power line frequency (120Hz for a 60Hz mains frequency). While flicker above 75 Hz is not noticeable to most individuals, the perceptibility of flicker is not just a function of frequency but also the relative intensity of the peaks and troughs of the light output waveform and the shape of the waveform, which describes the duration of varying light levels over time within each cycle .

most of the lower cost (<$5 ) led bulbs on the market is indeed flickering significantly . The question is how much flicker is still acceptable to human eyes ?

If you live in California , there is local energy energy code to support get better quality of light on LED light bulbs/fixtures. The California Energy Commission updates the Building Energy Efficiency Standards every three years.

In CEC Title 24 and Title 20 , there are special code for dimmable led light bulb and fixtures ,that need to be able to meet the low flicker requirements.

California’s requirements include the test method “Joint Appendix 10” (JA10) that requires measuring the light output of a source or luminaire and dimmer for two seconds and then running the data through several complex calculations to evaluate flicker at multiple frequencies up to 400 Hz. Title 24 requires high efficacy sources to be “low flicker operation”, which means that the LED product will have less than 30% flicker at frequencies below 200 Hz. Here is what percent flicker means, the waveform on Y axis is light output measurement , the cycle on X axis is the one cycle duration of the repeated waveform.

You can find more about the quality of light on this whitepaper from Philips.

In summary, we reviewed some history about the LED ,what is in a typical led light bulb, how to select a good bulb for your application ,what makes a good led light bulb.

I will highly recommend the energy star certified bulb ,and it normally means a better quality even the extra price could worth it over its longer lifetime.

Related Posts

Sign up for SMART LIGHTING UPDATES