How to Choose LED Bulbs: Lumens, Kelvins and CRI Explained

At first glance, choosing an LED bulb seems simple: pick one up, screw it in, done. But once you start digging, it is easy to get lost among wattage, lumens, kelvins, CRI and a host of other parameters. This guide explains in plain language what each of them actually means, which ones matter most, and how to tell a quality bulb from a cheap imitation in the shop. It is based on expert insights from the Lithuanian national broadcaster LRT programme "Vartotojų kontrolė" (Consumer Control), combined with our own experience as lighting professionals.

What matters most when choosing an LED bulb?

Four parameters matter most: luminous flux in lumens (how much light you get), colour temperature in kelvins (warm or cool light), the colour rendering index CRI (whether colours look natural) and the cap type (whether the bulb fits your fixture). Wattage, contrary to habit, is today only a secondary indicator.

Below we look at each parameter in detail – with concrete numbers you can apply on your very next shopping trip.

Lumens or watts: which actually tells you how much light you get?

The amount of light is measured in lumens (lm), not watts (W). Watts only measure electricity consumed. In the incandescent era wattage was a convenient shorthand because all bulbs were equally inefficient. With LED technology that link is broken: bulbs of identical wattage can emit very different amounts of light.

Experts on the LRT programme pointed out a common manufacturer trick: the packaging advertises high wattage at a low price, the buyer expects plenty of light – and ends up with considerably less than they should get. So always look for the lumen figure first.

Rule of thumb: a quality LED bulb delivers roughly 80–110 lumens per watt. If the packaging figures work out much lower, the bulb is inefficient.

Which colour temperature should you choose for each room?

In short: warm white (2,700–3,000 K) for living rooms and bedrooms, neutral white (4,000 K) for work areas. Colour temperature, measured in kelvins (K), describes the tint of the light – from cosy yellowish to bluish white.

In Lithuania warm-spectrum 2,700–3,000 K bulbs are the most popular and most widely accepted – they create a relaxing, cosy atmosphere. Neutral 4,000 K light suits spaces that call for focus and productivity: a home office, the kitchen worktop, the bathroom mirror. Cooler tones (5,000 K and above) are usually reserved for public spaces or a deliberately cold "hi-tech" aesthetic.

One golden rule: do not mix different colour temperatures within one space – even quality lighting will look untidy.

What is CRI and why does it decide how your home looks?

CRI (colour rendering index) shows how natural colours appear under a light source. The scale goes up to 100: the higher the number, the truer the colours. The minimum for a quality LED bulb is CRI 80, while premium bulbs now reach 90 and above – approaching the level of incandescent and halogen lamps, once the benchmark.

If you feel that LED lighting "distorts" colours – food looks dull, wood greyish, skin tired – a low CRI is usually to blame. Poor figures are typical of no-name bulbs that reached the market through questionable channels.

A memorable comparison from the LRT programme: the old orange street lamps have a CRI of only about 30 – the limit at which you can still tell blood from petrol or coolant on the tarmac. At home you clearly deserve better.

How to pick the right cap type?

The cap is the bulb's connection to the fixture. Before buying, check the marking on the bulb you are replacing or the fixture specification. The most common types in Lithuanian homes:

• E27 – the large screw cap, the classic standard for pendant and table lamps;
• E14 – the small screw cap, common in chandeliers and decorative fixtures;
• GU10 – twist-and-lock, typical for directional ceiling spots;
• GU5.3 (MR16) – low-voltage spotlights (a transformer is required);
• G9 and G4 – small pin caps for compact fixtures.

How to spot a quality LED bulb in the shop?

Quality is hard to judge by eye, but several signs are reliable:

• CE and RoHS marking. Bulbs officially imported into Lithuania must carry these certificates and are strictly checked at customs. Bulbs ordered individually from foreign marketplaces may have no certification at all – and the parameters on the box may be pure fiction.
• Weight. A surprising but practical expert tip: the heavier the bulb, the more likely its cooling is properly engineered – and a well-cooled bulb lasts longer.
• Test before you buy. Ask the seller to screw the bulb into a live socket. The consumer rights authority stresses that electrical goods of satisfactory quality are exchanged or returned only at the seller's discretion – so if you discover a dead bulb at home, the dispute will be much harder to win.
• A clear manufacturer. A known brand is not a guarantee, but it is far less risky than an anonymous box.

Frequently asked questions

How many lumens does a room need?

A practical guideline for living spaces is about 150–300 lm/m² of general lighting: for a 20 m² living room that is roughly 3,000–6,000 lm spread across several light sources. Work areas need more – up to 500 lm/m².

Can I use an LED bulb with a dimmer?

Only if the packaging says "dimmable". A regular LED bulb on a dimmer will flicker or fail early. The dimmer itself must also be rated for LED loads.

Why does my LED bulb burn out sooner than promised?

If LED bulbs in your home last only a month or two, the cause is usually not the bulbs but the electrical installation – above all voltage surges. Read more in "Why do LED bulbs flicker and how to fix it".

Is a higher CRI worth the extra money?

For the living spaces where you spend most of your time – yes. CRI 90+ bulbs render skin, wood, textile and food colours far more naturally, and you notice the difference every day.

Summary

When choosing an LED bulb, look at lumens first, then match the colour temperature to the room, make sure the CRI is no lower than 80, and check the cap type. In the shop, pick CE and RoHS marked bulbs from a known manufacturer, prefer the ones with reassuring weight, and ask to test them before paying.

If you want more than a bulb swap – a properly designed lighting scheme for your home or commercial space – browse our LED bulb range or get in touch: we will recommend the light sources best suited to your space.

Source: LRT programme "Vartotojų kontrolė" – expert commentary on choosing light bulbs, supplemented with practical recommendations from our specialists.