I am gradually switching to LED bulbs at home. I believe that’s the way to go if you want to trim your electricity bill. These bulbs are super efficient in terms of power consumption, last longer and also have a nice glow. But I find the new terminology a bit confusing.

Let me explain: In the days of incandescent bulbs—those round bulbs that we grew up using —we had benchmarks for brightness: 40 watts, 60 watts, 100 watts and so on.

Some years ago, we switched from the power-guzzling incandescent bulbs to the more energy-efficient CFLs (compact fluorescent lamps), and we learned, by trial and error, that for light equivalent to a 100-watt bulb, one would require a 20- to 23-watt CFL (I hate the design; they stick out of shades).

I now want to switch to LED (light emitting diode) bulbs: Yes, they are still quite expensive, but the prices are coming down.

I am looking for an LED bulb with brightness comparable to a 100-watt incandescent bulb or a 23-watt CFL, but I don’t have a benchmark for wattage of LED bulbs: I do not know how many LED watts will give light equal to standard 100 watts. Would a 12-watt LED bulb be enough? I don’t want to make an expensive mistake.

And this is what I’ve picked up from the Net: As you switch from incandescent bulbs and CFLs to LEDs, you have to learn a new word—“lumen". It’s a measure of brightness.

A comparison of watt and lumen output for different types of bulbs.

You’ll find any number of simple charts on the Net that explain the watts-to-lumens ratio. Even if there’s a slight difference in the watt and lumen figures over two sets of charts, you get a good idea of what to look out for when buying an LED bulb.

So to replace a 100-watt incandescent bulb or an equivalent 23-watt CFL, I should ideally get an LED bulb that gives me more than 1,300 lumens. According to the charts, an LED bulb that gives light equivalent to a 100-watt incandescent consumes only 18 watts of power. But again: check the package for lumens.

The scientists who invented the key piece of technology behind LEDs won this year’s Nobel Prize in Physics. The Nobel press release says, “The most recent record (for LED efficiency) is more than 300 lumen/watt, which can be compared to 16 for regular light bulbs and close to 70 for fluorescent lamps… LEDs last up to 100,000 hours, compared to 1,000 for incandescent bulbs and 10,000 hours for fluorescent lights."

Talking of longevity, I came across an interesting story on the Net. In 1924, the manufacturers of incandescent light bulbs formed a cartel to deliberately reduce the lifespan of their bulbs. The purpose was to increase the sales, and make more money.

The group, known as the Phoebus Cartel, reduced the expected life of a light bulb to 1,000 hours. Till then, the lifespan of a bulb was around 2,000 hours. In short, the manufacturers engaged in large-scale “planned obsolescence". The cartel carried on for nearly 15 years before it collapsed at the start of World War II.

Since then, we’ve come a long way in terms of efficiency.

However, in India, as things stand, not all companies print the lumens upfront on the box. And my neighbourhood shopkeeper doesn’t have a clue when I ask him about lumens. Even when you shop online, several brands of LED bulbs don’t give lumens in “product details". On the other hand, if you look at product details on the LED bulb package on any foreign website, it will mention the lumens upfront.

The other information that helps you choose an LED bulb is light temperature which determines its colour—warm or white. It is measured in Kelvin (K). The temperature ranges from 2,700-5,000K—in which the lower number indicates warm light. For daylight tones, the suggested temperature is 5,000K.

For my reading lamp, I have switched to a 1,055 lumen, 12.5 watt, warm white (3,000K) LED bulb. I feel it’s as bright as the CFL I replaced, and the glow is much nicer. And the good thing is even if I doze off with the light on it won’t burn a hole in our monthly budget.

Shekhar Bhatia is a science buff and a geek at heart.

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