Lumens and LEDs – How Bright Should My Room Be?

LED lighting can seem like a whole new language if you’re used to incandescent light bulbs. For incandescents, a bulb’s power supply (wattage) could give a reliable measure of brightness. But for LEDs, power is no longer a good guide – because they can output comparable levels of brightness with far less wattage.

So what’s the best way to compare LED lighting products? Let’s take a look at the six-and-a-half numbers that really matter…

  1. Lumens: Sometimes called lm, lumens measure the ambient light coming from a light source. The higher the lumens, the more brightly lit a room will be. As we move away from incandescent lighting, lumens are becoming the most useful measure of the actual light output across different lighting products.
  1. Colour Temperature: Measured in degrees Kelvin (K), colour temperature indicates the tone or ‘warmth’ of light. Colour temperature of 2600-2700K gives out warm light (similar to incandescent bulbs), while higher colour temperatures around 4100-5500K produce a cooler whiter light. Colour temperature affects how bright a light looks, meaning that light sources may appear different even if they are outputting the same lumens – lights with colour temperatures above 3000K (the colour of daylight) typically appear brighter.
  1. Colour Rendering Index (CRI): Represented as a value from zero to 100, colour rendering index shows how accurately a light source produces colours. Lights with low CRI values (20-30) tend to dilute and diffuse colours, and so are best for applications where accuracy is less essential.
  1. Candlepower: Measured in candelas, candlepower indicates the intensity of light thrown in a specific direction. Candlepower is less relevant for room lighting, and more vital in installations where the power of a concentrated beam is more important than the area it illuminates.
  1. Life Hours: The operational life expectancy – calculated by measuring the hours taken for half of a test batch to burn out. (The same calculation as a radioactive half-life.) It’s a good indicator of the life you can expect from an LED, but because it’s an average, don’t treat it as a guarantee.
  1. Wattage …and 6½. Voltage:

LED downlights

Games room

Matching Up The Numbers

To light your home the way you want, the most important number is going to be the lumen value of your LEDs.

That’s because if you’re replacing an incandescent bulb, then an LED claiming the equivalent wattage could still be the wrong choice. Sounds ridiculous, but it’s true. Here’s the catch: sadly there’s no standard for calculating the equivalent wattage, and conversions vary from one manufacturer to another. So to choose the right replacement, you’ll get better results by comparing the lumen value of your old incandescent bulb to that of its potential replacement LED.

If you don’t know lumen values for your old bulbs, this table offers some figures for the lumen values of incandescent bulb brightness, by wattage. Estimates only!

Incandescent bulb wattage Estimated lumen equivalent
25W 250
40W 450
60W 800
75W 1,100
100W 1,600
150W 2,600

Wedding venue LEDs

How Bright Do You Need?

Remember how we said lumens measure ambient light output? That means the more lumens, an LED puts out, the more brightly lit a room will be. So the question you’ll need to answer is, how big is my room and how many lumens will I need to light it?

Here are some guideline figures, depending on the kind of surface you’re lighting:

20 lumens / sq ft for normal (floor) lighting.

30 lumens / sq ft for tables and countertops.

50 lumens / sq ft for reading and other tasks.

Some examples…

Example area Surface type Estimated lumens required
15 x 20 ft (300 sq ft) Living room (floor) 6,000
4 x 4 ft (16 sq ft) Dining table 480
3 x 3 ft (9 sq ft) Bedside lamp (reading) 450

Of course you should combine lighting levels in rooms where you use different areas for different purposes. So if the living room example above has your 5×3 ft computer desk in one corner, the room (300 sq ft) will need around 6,000 lumens – with an additional 750 lumens for the desk (15 sq ft).

If walls, furniture or other surfaces are particularly dark colours, then you should increase the brightness of your lights. And your own preferences are important too – personally I prefer things a little bit dimmer, but if you like more light then you’ll want to add another 10 or 20% to the numbers above.

Living room LEDs