LED Lighting Explained: Lumens, Watts, CRI & How to Buy Well

A selection of LED bulbs and panels showing different shapes and colour temperatures

The LED quietly won the lighting world in barely a decade, and for good reason: it produces the same light as an old bulb for a fraction of the power, lasts many times longer, and comes in every colour and shape. But it also changed how you buy light — the old habit of asking for a "60-watt bulb" no longer works, because an LED gives that brightness for 8 watts. This guide explains how LEDs work, how to read their labels, and how to tell a good one from a cheap one that will flicker and die early.

It sits under the home lighting design guide and pairs with the colour temperature guide.

The safety line. Choosing and replacing plug-in LED bulbs is ordinary homeowner territory; hard-wired fittings, downlights and drivers are installed by a licensed electrician. For safety and performance, choose lamps conforming to IS 16102 (self-ballasted LED lamps) and, ideally, BEE-rated for efficiency.

Why LED replaced everything

An LED (light-emitting diode) produces light by passing current through a semiconductor, rather than heating a filament (incandescent) or exciting gas (CFL/tube). That difference gives it three decisive advantages:

Efficiency — it turns far more of the electricity into light and far less into heat, so it uses a fraction of the power for the same brightness.
Life — it lasts many times longer than incandescent or CFL, so you replace it far less often.
Control — it switches instantly, dims well (with the right driver), and comes in any colour temperature.

The incandescent bulb is effectively obsolete, and the CFL is on its way out; for a modern home, LED is simply the answer — as the LED vs CFL vs halogen comparison below makes plain.

Reading an LED: the numbers that matter

Four numbers tell you almost everything about an LED. Learn them and you will never be mis-sold a bulb.

What	Unit	What it tells you
Brightness	lumens (lm)	How much light — the number that replaced "watts"
Power	watts (W)	How much electricity it uses (your running cost)
Efficiency	lumens per watt (lm/W)	Light per unit power — higher is cheaper to run
Colour	kelvin (K) + CRI	The warmth of the light and how true colours look

Lumens is brightness. Roughly: 400 lm ≈ old 40 W bulb, 800 lm ≈ 60 W, 1,500 lm ≈ 100 W. Buy by lumens.
Watts is now just the running cost. Lower watts for the same lumens = cheaper to run.
Efficiency (lm/W) is the number that decides your electricity bill: a good modern LED delivers roughly 90–120+ lm/W. Compare lumens-per-watt between products, and look for the BEE star rating — more stars means more light per unit of power.
Colour — the kelvin number (warm 2700K to cool 6500K) and the CRI (colour accuracy) — is important enough to have its own colour temperature & CRI guide.

Diagram comparing an old 60 W incandescent bulb and a 9 W LED both producing 800 lumens, showing lumens as brightness and watts as running cost

LED vs CFL vs halogen

Feature	LED	CFL	Halogen / Incandescent
Efficiency (lm/W)	Highest (~90–120+)	Moderate (~50–70)	Lowest (~10–20)
Life	Longest	Moderate	Shortest
Switch-on	Instant, full	Warms up	Instant
Dimming	Good (right driver)	Poor	Good
Contains mercury	No	Yes (dispose carefully)	No
Verdict	The default	Being phased out	Obsolete for general use

The conclusion is not subtle: for general home lighting, choose LED. CFLs linger in some fittings but offer no advantage; halogen and incandescent are for niche or decorative use only.

Telling a good LED from a cheap one

This is where money is won or lost, because the market is full of cheap LEDs that flicker, shift colour, or fail in months. Signs of quality:

Conforms to IS 16102 (self-ballasted LED lamps — safety and performance) and carries a genuine BEE star rating.
A real efficiency figure (lm/W) stated, not just a watt number.
Good CRI (ideally 80+, and 90+ where colour matters — see the colour guide).
No visible flicker — cheap drivers flicker (test with a phone camera in slow-motion), which causes eye strain and headaches.
A sensible warranty and a reputable brand — the driver, not the LED chip, is usually what fails, and quality brands use better drivers and thermal design.
Right fitting and dimmability — if you want to dim it, buy a dimmable LED and a compatible dimmer; a non-dimmable LED on a dimmer flickers and fails.

The cheapest LED is rarely the cheapest to own. A quality lamp that lasts years and runs at high efficiency beats a bargain bulb you replace twice a year and that quietly costs more to run.

The one-line answer

LED won because it makes the same light for a fraction of the power and lasts far longer — but it changed how you buy: think in lumens (brightness), treat watts as just the running cost, compare lumens-per-watt efficiency (and the BEE star rating) to decide your bill, and check colour temperature and CRI for how the light looks. Choose IS 16102-conforming, BEE-rated lamps from a reputable brand with a stated efficiency, no flicker and a real warranty — because the cheapest LED is seldom the cheapest to own, and it's usually the driver, not the diode, that fails.

Where to go next

The design context: Home Lighting Design Guide.
The warmth and accuracy of light: Colour Temperature & CRI.
Making it smart: Smart Lighting Guide.
Estimate what you need: Room Lighting Calculator.

References

IS 16102 : Part 1 : 2026 (Safety) and Part 2 : 2026 (Performance), Self-Ballasted LED Lamps for General Lighting Services, Bureau of Indian Standards.
Bureau of Energy Efficiency, Standards & Labelling programme (LED lamps): https://beeindia.gov.in/
IS 3646 : Part 1 : 2025, Interior Illumination — Code of Practice, BIS.
National Electrical Code of India, SP 30 : 2023, BIS: https://www.bis.gov.in/

Efficiency figures and equivalences are indicative and vary by product; check the actual lumens, lumens-per-watt and BEE rating on the pack. Hard-wired fittings must be installed by a licensed electrician. Verify any standard's status via the BIS catalogue before relying on it.