Why LED lamp?

Is it time to buy a LED lamp now?

Prerequisite:  Before reading this post, you should be well understanding relevant terms related to illumination and various light sources, look into this post if any doubt.

 

   Powered by modern LED lighting technology, the fourth generation of lighitng technology, LED lighting will be today and tomorrow’s priority illuminating solution, because

1. Higher luminous efficacy: LED lamp consumes much less energy while emits same or more luminous flux. comparing with traditional light sorces. Today's LED technology has achieved 100-110 lm/w efficacy which is outstanding versus 60-70 lm/W of other light sources.
     Luminous Efficacy Chart of various light sources
 

As a result, a LED lamp will save much of electricity bill by replacing other light source lamp. For example, a 18W LED T8 tube can be good replacement for a 40W fluorescent tube in office, assuming 8 hours daily usage and $0.26/KWh tariff rate, one tube saving in one year could be as much as: (0.040-0.018) x 8 x 365 x 0.26 = $16.7

2. Good emitting directivity:

LED light luminous flux, by nature, are all confined and emitted from a semiconductor flat surface with beam angle less than 180 degree and be able to achieve higher luminance and illuminance. Comparing with other 360 degree emitting light source which rely on lighting fixture's reflection and have at least 30% lumens wasted, it is very easy for LED lamp to have its all luminous flux become effective illuminance.

As you can see from below comparison of fluorescent tube and LED tube, Luminous flux of a fluorescent tube are equally emitted in 360 degree all directions, about 80 degree flux upward are almost wasted due to non-effective reflection, about 80 degree flux toward each side are relying on fixture's reflection and incurring loss; whereas LED light will make its 90% flux downward and becoming effective illuminance with beam angle less than 180 degree.

   Fluorescent tube in luminaire          LED tube in luminaire
 

That is why a 18W LED tube with 1800 lm will be able to provide you same or better effective illuminance as a 40W fluorescent tube with 2400 lm provided.

3. Good lumen maintenance:

Unlike Fluorescent or HID light source with evaporable luminescent substance such as mercury and argon gas, LED is non-evaporable semiconductor luminescent substance which is able to keep light emitting capability in long time. For example, In case your application require 90% of designed illuminance (initial illuminance), Fluorescent only work for 8000 hours before you have to change it.

   Lumen Maintenance Chart

Note: Product lifespan may not be as long as Lumen maintenance curve showed, in case of fluorescent product, shorter lifespan of its electrodes which is usually made of Tungsten filament will shorten Fluorescent product lifespan. That is why most fluorescent including CFL product are having lifespan about 8k-10k hours instead of 20k hours showing in curve before 80% lumen drop. In reality, most fluorescent lamp product failed on electrode filament broken rather than luminance fadeaway.

4. Better CRI:

Most of LED lamp have CRI range from 75 to 85, comparing to fluorescent and metal halide lamp range from 60 to 80. As you can see from spectrum output of respective light source, LED has better light power output in every wavelength of visiable light than other two light source which is short of output in certain wavelength range.

 :LED Spectral Output

 Fluorescent Spectral Output

 Metal Halide Spectral Output

5. Very long lifespan:

From lumen maintenance curve, we know LED has 40k hours lifespan before its lumen output drop to 80% of initial output. If your application minimuim requirement is 80% of designed illuminance, LED lamp product will have similar lifespan as LED product has neither electrode filament to be broken nor luminescent substance to be evaperated. Even based on 10 hours usage per day, a LED can easy last more than 10 years (10 x 365 x 10 = 36,500 hours). So LED lamp's lifespan will be depending on its driver's lifespan in most of product scenario. Today, a good quality LED driver can also achieve 30k-40k hours lifespan. So you can surely expect a LED product lifespan at least 6-8 years.

 LED lifespan comparison chart

6. User friendly:

Unlike fluorescent lamp, LED lamp has no balast, no starter, it is turned on instantly, therefore, no noise, no delay.

7. Green and Eco-friendly:

LED lamp has no mercury content at all, and generate much less amount of heat. It is a green product and provide you a low-carbon and Eco-friendly life style.

 CFL non-disposable          LED is Eco-friendly

Same as other electronics product, LED lamp become Eco-friendly and disposable only when it is manufactured based on RoHS (Restriction of Hazardous Substances) requirement. Do remember to buy RoHS compliance LED product.

Note: Since Fluorescent and CFL product must contain mercury, they are non RoHS compliance product by nature.

8. Flicker-free light:

Unlike fluorescent or CFL which luminescent substance is excited by sinewave current causing unstable light intensity, LED is driven by constant DC current with constant light intensity output, therefore, LED light is flicker-free light, it will relax your eyes every day.

 Flickering light          Flicker-free light

Since Fluorescent light is flickering at 100Hz, Human brain will not be able to identify the flicker, but human eyes will see the flicker and feel tired faster than a non-flicker light such as sunlight or LED light being seen.

9. No UV light emitting:

LED lamp emits no ultraviolet (UV) at all, so insects will no long fly into your room, have windows opened and enjoy a windy night with a beautiful moon! Most of insects are attracted by 350nm~400nm wavelength light which belong to UV light spectrum and is out of human eyes response.

 LED emit no UV light

As you can see from above spectral output chart, LED output start from wavelength 420 nm and longer, no output wavelength shorter than 400 nm at all.

 

Summary and comparison

 

10 years comparison (assuming 8 hours daily usage and $0.26 tariff)

Lamp type

Incandescent lamp

Incandescent

Metal halide lamp

Metal Halide

Fluorescent or CFL lamp

CFL bulb

LED bulb

LED bulb

Watt Rating (W) 60 20 14 7
Lumens output (lm) 900 950 (Average) 900 700
Luminous efficiency (lm/W) 15 45 60 100
CRI >90 >60 >70 >80
Lifespan 1500 4000 8000 35000
Electricity bill $456 $152 $106 $53
Replacement number 19 7 4 1
Cost per bulb $2 $12 $5 $9
10 years total cost $494 $236 $126 $62
Full range dimmable Yes Some NO Yes
Lumen-maintenance Poor Poor Medium Good
Light flickering NO Yes Yes No
turn on instantly Yes Some delay Some delay Yes
on/off frequency effect to lifespan shorten lifespan some effect some effect NO effect
Heat emission amount high (80 btu's/hr) high (60 btu's/hr) medium (20 btu's/hr) Low (4 btu's/hr)
UV emission / insect attractive Yes Yes Yes NO
sensitive to temperature Some Some Yes (low temp problem) NO
sensitive to humidity Some Some Yes NO
Hazardous material  None 3mg Mercury/bulb 5mg Mercury/bulb None
Disposable Some (50%) No (contain mercury) No (contain mercury) Yes (100%)

 

"OK, LED product is good enough, but it is too expensive now and expected further price drop next year or two. So I better wait."

Wrong! This assumption may be right a years ago, but no longer valid today. From beginning of this year, some LED lamp have goen into mass production and price has dropped to a level comparable to fluorecsent lamp. For example, this 12W LED circular ceiling lamp selling at S$22.8 is totally comparable to its replacement of 24W fluorescent lamp set, same as this 18W LED circular ceiling lamp to its replacement of 36W fluorescent lamp set.