Knowledge Base

Lighting accounts for almost 20% of the monthly electricity consumption in many households, and using new lighting technologies can significantly reduce energy use in the house. However, when it is time to make a choice among the lighting products, one notices that bulbs vary by their type of technology, their brightness, the amount of energy they use, the beam spread and the light color emit. With so many kind of bulbs available on the market, many are getting confused. Here are some basic information that may help you.

LED emits light when voltage passes through a semiconductor material (a light emitting diode) embedded in a plastic capsule. Assembled into a light bulb, LEDs come to full brightness without need for a warm-up time. Their lifespan and electrical efficiency is several times better than incandescent lamps and significantly better than most fluorescent lamps. On the other hand LEDs emit light in a very narrow band of wavelengths and their directional characteristics affect the design of lamps. Although LEDs are currently more expensive on an initial capital cost basis, when considering the total cost during its long useful life, they are much less expensive to run.

A compact fluorescent light (CFL) uses a tube and a compact electronic ballast in the base of the lamp. The tube is curved or folded to fit into the space of an incandescent bulb and can produce warm tones of light. CFLs use 20-40% less electricity and last 8 to 15 times longer than standard incandescent lamps. CFLs are more expensive to purchase but in the long run they represent a much better economical option. However when you get rid of an old CFL it will likely break if buried in landfills and release toxic mercury vapor, which can contaminate water and enter the atmosphere. Unless Auroville can ensure a take-back system for such harmful waste, we cannot recommend changing ordinary bulbs with CFLs

An incandescent bulb produces light when an electric current passing through a wire filament heats it to a high temperature and makes it glow. Incandescent bulbs vary from 15 to 150 watts and produce usually a soft yellow-white light emitted in all directions. Incandescent bulbs are much less efficient than most other types of electric lighting. They convert less than 5% of the energy they use into visible light (with the remaining energy being converted into heat).

A halogen lamp is an incandescent lamp that has a small amount of a halogen such as iodine or bromine added. They produce a bright, white light of a higher luminous efficacy than incandescent bulbs. Halogen lamp can be operated at a higher temperature so they require more caution when handling. The small size and intensity of halogen lamps make them great for task lightning (e.g. compact optical systems for projectors and illumination).

For a night lamp many are using a “Zero watt” bulb, which is called so due to the inability of the older meters to accurately measure their power consumption. But now the advanced meters ensured that even a fraction of a power consumed by any appliance does not go unnoticed. Therefore Zero watt bulbs do consume at least 5 W of power and since some people switch them on 24h a day, it means that such small bulb consumes 45 kWh per year. If you need a night lamp, there are several LED alternatives available these days that consume just 1 W and produce almost the same amount of light. And LEDs being long lasting, it will keep it going for years.

When shall I replace existing light bulbs?

Considering the sum of all the energy required to produce a light bulb, it should only be replaced when it has completed its life, and not during its life cycle. Wastage of embodied energy is as bad as wastage through inefficient energy usage.

Energy efficient light bulbs

For decades nearly everyone filled their house with incandescent bulbs and brightness was measured in watts. Its measurements was featured on the front of each light bulb package, even though watts are the indication of how much power a bulb consumes – not the amount of light it generates. With the introduction of energy-saving bulbs using a lot less power to produce the same amount of light, reliance on watt measurements alone make it difficult for people to compare traditional incandescent bulbs to more efficient bulbs.

Nowadays the efficiency of a light bulb is defined in lumens and watts and new efficiency standards require lightbulbs to consume less electricity (watts) for the amount of light produced (lumens).

What is Lumen?

Lumens is a measure of brightness indicating how much light you are getting from a bulb. More lumens means that it is a brighter light; if you want something dimmer, go for less lumens. You can use the following chart to see equivalent watt and lumen (Brightness) for different types of bulbs.

As shown in the above chart, to have 700 lumens of light, you can either chose a:

• 10 watts LED bulb, which is more energy efficient and has a life time of 25,000 hours.
• 12 watts CFL lasting 12,000 hours.
• 42 watts Halogen having a life time of 2,500 hours.
• 60 watts incandescent bulb with a life time of 1,000 hours.

Lightbulb efficiency is also measured in terms of lumens per watt—the amount of light produced for each watt of electricity consumed:

So whenever buying new bulbs, think lumens – not watts.

Useful Links:

Bijli Bachao

Bureau of Energy Efficiency