In our locality the supply voltage often goes below 200 volts after sunset. The situation is such that Tube lights and PL lamps with magnetic ballast fails to strike. One solution is to fit CFL lamps or incandescent bulbs, I had installed multiple CFL lamps in rooms because of their higher energy efficiency. But CFL bulbs fitted in kitchen, bathroom and stairs fail pretty quickly because of frequent on/off cycle. They hardly last for more than 2000 hours. This inherent problem of CFLs(specially cold start type) is well documented so I am not going in the details.
For an alternate solution I searched and found that LED lamps(Light emitting diodes) are available in our local market. I purchased it from an online store at 660/-. The bulb arrived 10 days later.
LED lamps are well known for many years but their use for household purpose was restricted because of low light intensity. Recent development in solid state electronics has improved their light output. LED lamps(in form of strip light, bulb, spot light) are vastly sold in European and American markets for illuminating homes, offices, streets or for decoration. In India until recently LEDs were mostly used as decorative lamps or as indicator lamps.
A LED bulb is a light-emitting diode(LED) product that is assembled into a lamp(or light bulb) for use in lighting fixtures. LED lamps have a lifespan and electrical efficiency that is several times better than incandescent lamps, and significantly better than most fluorescent lamps. The LED lamp market is projected to grow more than 12-fold over the next decade.=Like incandescent lamps and unlike most fluorescent lamps(e.g. tube lights and CFLs), LED lights come to full brightness without need for a warm-up time; the life of fluorescent lighting is also reduced by frequent switching on and off. White-light LED lamps have longer life expectancy and higher efficiency(more light for the same electricity) than most other lighting. A typical domestic lamp is stated to have an "average life" of 15, 000 hours(15 years at 3 hours/day), and to support 50, 000 switch cycles.
With advancement of electronics efficiency of LEDs are increasing, cost per lumen and output per device have been improving rapidly according to what has been called Haitz’s law, analogous to Moore’s law for semiconductor devices. Haitz’s law(based on observation) states that in every decade, the cost per lumen(unit of useful light emitted) falls by a factor of 10, and the amount of light generated per LED package increases by a factor of 20, for a given wavelength(color) of light. Besides the forecast of exponential development of cost per lumen and amount of light per package, it also forecast that the efficacy of LED-based lighting could reach 200 lumen / Watt in 2020.
Technically speaking, at present two types of LED bulbs are now manufactured by Philips. In the first variety the phosphor is fixed onto LED chips. LEDs emit blue or violet light which is readily converted into blue-white / yellow-white light. The other type is costlier, It contains arrays of Blue and red LEDs at the centre. The phosphor is fixed in the inner layer of bulb dome. bright blue light emitted from blue LEDs falls on the phosphor skin and is converted there into white light. This remote phosphor excitation technology(similar to tube lights) reduces the glare and improves light quality. The red LEDs are attached to maintain high colour rendering index(CRI) value. Generally LEDs have CRI value near 80 but Philips remote phosphor LED bulbs have CRI value near 90. Higher the CRI value more accurately it will reproduce colour. Sunlight has the highest CRI value 100, also incandescent bulbs when operated at rated voltage has 100 CRI value. Only the first variety is available in India.
When I had searched I found four major companies(Philips, Havells, Wipro, Osram) are selling LED bulbs with retrofit holder(B22) options. B22 holder is used in most part of india in some applications E27 holdres are found. Philips is a well known brand for making lights. So I selected Philips.
Philips LED bulbs, till now, are available in two varieties in India. One type is called warm day light(colour temperature 2700-3000K) and other type is cool day light(colour temperature 6500K). Light output from warm day light variety resembles incandescent bulbs where as cool day light variety resembles the white light from CFLs or tube lights. I personally like white light with(with slight green/blue hue). So I choose the cool day light variety.
First thing you will notice that the bulb is tad heavier because of aluminum heat sink attached at the bottom. I had fitted the LED bulb without any hassle. The LED bullb looks like a regular size incandescent bulb.
Now pros:
1) Highly energy efficient, at 10W it outputs 806 lumens. I compared it with CFLs and found the 15 W Philips Tornado CFL, cool day light variety has 950 Lumens output. So it has slightly lower light output. But the bulb is very bright so you will hardly find any difference.
2) Although the bulb is rated for 220-240 volts. It works as below as 160 volts.
3) Switch on is instant.
4) I think it can withstand the frequent on/off cycles. Because LEDs are suitable for applications those require frequent on-off.
5) I could not hear any hum or noise from the electronic circuit. With sine wave inverter it works fine.
6) It consumes only 10 watts, so it will save lots of battery power during long power cuts and with sine wave inverter it makes no interference. But I don’t know what will happen if used with square wave inverters.
7) Light aluminum base becomes somewhat hot after long use but much less than incandescent bulbs. So heat output is very low.
8) No mercury is used, so more environment friendly than CFLs. I don’t know whether they have used any other heavy metals or environment pollutants for electronic circuits or not
9) No UV radiation, so no risk of exposure to harmful UV-B or UV-C radiations.
Now the disadvantages:
1) Cannot be used with enclosed light fixtures where the produced heat is trapped. This will shorten the life of the bulb.
2) Very high price. It cost approximately 650/-. At such high price how many can afford this? With wide spread use the price might come down. I have also heard that a change in LED chip manufacturing technique will bring down the price soon(1/10 th of current price).
3) Only two light output colour options are present . The best colour according to me(5000K, bright day light) is not available in India.
4) A relatively narrow light wattage variety are available at present. Highest is 10 watt. lowest is 0.5 watt.
5) Although it is stated on the pack that the bulb will last up to 10 years for 4 hours use per day, I could not find any warranty in the pack. I think they should have provided at least two years replacement warranty for such a costly product.
6) Light is bit directed, so best works when fixed in downward light fittings. But I have fixed it in horizontal position, and I have faced no problem.
7) Light is very bright so it better to fix it in a holder where you can avoid direct stare. Like bulb holders located near ceiling.
8) LED lamps are known for their long life(50000-100000 hours or more), But the Philips variety has expected life of 15000 hours. Why such a short life time? I researched on it and found that the possible reason behind could be either the LED chips are over worked or the components(specially the electrolyte capacitors) used in the circuit board are made of cheap materials. This is very much disturbing. After spending so much I came to know that the LED bulb by Philips sold in India has 1/10 life of an actual LED light. It is a mere wastage of natural resources if the whole lamp fails because of cheap circuit components.
Otherwise, after using it for a month I am satisfied with the light output and my primary reason(light at low supply voltage) for purchase is absolutely covered. Also I use it to save battery power during power cuts. These type of lamps are most suitable energy efficient light sources other than CFLs. They are also environment friendly(major concern for a densely populated country like India).LED bulbs at lower price will definitely increase their mass acceptability.