When deciding which bulb to by, the first question to ask is how much light do you need. (Mark Lennihan/AP)

Technology transforms lighting design at lightning speed, yet there is still no bigger bang-for-the-buck upgrade to your home lighting than simply choosing the right lightbulb.

But how do you choose when faced with a mind-bending array of standard incandescent bulbs, florescent tubes, compact florescent swirls, halogen pucks and LEDs that mimic them all? Especially as most of us buy bulbs by using descriptions like “Soft White,” “Reveal” or “Daylight,” which tell precious little about the light that the bulbs cast.

Hope is to be found on the side of most bulb packaging. It’s called the “Lighting Facts” label. It offers some scientific-sounding measurements that tell you everything you want to know — once you understand how to read them.

As a matter of practicality, people today are likely to replace fluorescents and incandescents with LEDs, which last 25 times longer and use far less energy. But once you understand how to read the lighting facts panel, you should be able to exchange any kind of bulb with any other kind of bulb and still achieve the effect you want.

To get started you need to understand the most critical measurements, lumens, kelvin and the color rendering index.


The first question to ask yourself, according to Terry McGowan, director of engineering for the American Lighting Association, is: How much light do you need? To get an answer, he said, “unfortunately means learning what an lumen is.”

A lumen measures quantity of light — how bright it is. “More lumens translate to more light,” said Shaun Fillion, who runs the Masters in Lighting Design program at the New York School of Design.

Many people are used to choosing brightness based on watts. Watts measure how much electricity a bulb uses “but no longer indicates how bright a lamp might be,” Fillion said. The lumen measurement is more precise. “If you have a lightbulb you want to match, look to match the lumens,” said McGowan.

Watts are still listed on bulb labels, but watts and lumens aren’t related the way they used to be. If you can’t deal with lumens, McGowan said, a rule of thumb is to divide the wattage of an incandescent bulb you are replacing by four to get something equivalent in an LED bulb. So an old 100-watt incandescent can reasonably be replaced by a 25-watt LED bulb.

Color temperature

The next important measure is Correlated Color Temperature. “Temperature is measured in kelvin,” McGowan said. “It’s an odd scale, but blame it on the kelvin people.” This scale tells you how amber or blue a light appears to be, and does so precisely, unlike the designations like soft-white or daylight.

There is a bit of jargon around color temperature. Amber shades of light are called warm, the white-blue shades are called cool. Warmer shades resemble rising and setting sunlight, cooler shades are similar to bright daylight. Colors typically run from 2700k (warmer) to 6500k (blue white).

There is no best color, it’s a matter of personal preference. But experts suggest that you pick a color and stick with it. “I’ve been in rooms with mixed warm and cool bulbs, and pretty soon your head wants to explode,” said McGowan.

If you are starting from scratch, McGowan suggests that you get a selection of bulbs and try them out in a room at the time of day you use them most. “It is worth getting one sample of each, and then try it out, because some people are surprised. There is a difference between 2700 kelvin and 3000 kelvin.” You can usually return the ones you don’t want. To approximate daylight color, find a bulb at around 5000 to 6500 kelvin.

Color rendering index

The most overlooked measure, but in some ways the most critical, is the Color Rendering Index. That tells you how accurate colors look under the light. “The Color Rendering Index is more important for me than lumen output,” said Rosemarie L. Allaire, a California-based residential lighting designer. Good color rendering light lets you tell whether a sweater is navy or black.

The CRI, as it’s called in the industry, is a scale from zero to 100. “Daylight is 100. You can’t render it better than that,” said Allaire. “When I am looking for an LED replacement for myself or a client, the first thing I look for is color rendering, and if it’s not 90 or above, I don’t buy it.”

A light can be a warm amber, and still score high on the CRI scale. “Even in yellow, high CRI Light, blue artwork should look blue,” said Fillion.

How high does CRI need to be? “Most are around 80. If you get higher, 90 or 95, things will look more colorful to you. The higher the better for residential uses,” said McGowan. “You can really change the look of a room by changing to bulbs with a higher color rendering index.”


There is still the matter of dimming, which gets complicated if you are using anything other than old fashioned incandescent lights.

Whether your wall dimmer will work with a given bulb — even one that says it is dimmable — still depends on the kind of dimmer you have. To make it even more confusing, some bulbs can be dimmed by more than one kind of dimming switch, but not necessarily all dimmer switches. You can check the specifications, but even that is no guarantee. The best choice is to take a bulb home and try it.

The National Electrical Manufacturers Association is making it easier if you are buying new switches, by marking both switch and bulb packaging with an icon that assures they will work together.

Smart bulbs

But some LEDs offer another way to dim, using smart technology and a wireless connection like WiFi, Bluetooth, ZigBee and can be controlled by Alexa, Siri or Google Home. This technology puts the dimming technology in the bulb itself, rather than in the electrical switch.

These LEDs also offer other features that you won’t find in common bulbs, like the ability to change colors, to turn on at specific times, and to control the color and brightness they will be during different times of day.

Smart bulbs, like the Philips Hue, can wake you up with a warm pseudo sunrise that turns blue-white over a few minutes, stays blue-white through the day, then becomes dimmer and more amber as bedtime approaches.

That is particularly valuable, said Fillion, because more and more research shows that daylight colored bulbs can disrupt your ability to get to sleep. “It’s all about the melatonin,” he said. “Reducing blue light allows production of melatonin to help you get sleepy.”

If it still sounds too complicated, said Allaire, there is an easy solution: “Hire a lighting designer.”