Lighting Terminology Explained
Randall Whitehead, IALD, proves a learned and gracious guide through lighting's labyrinthine lexicon.
 
A 2,700K fluorescent lamp has all the visual warmth of an incandescent, so you can look good and feel good about saving energy at the same time.
Randall, help! Footcandles, candelas, lux, lumens, Kelvin—what’s a guy to use regarding light in a room? One measurement says one thing; info regarding a fixture says another. Also, my customers always want “natural light” and as much “daylight” as possible.

I agree. There are too many terms out there, making lighting less clear to both homeowners and professionals. Here are the official definitions:

Footcandle: The unit measurement of luminance equal to one lumen per square foot; originally referring to a candle burning 1 foot away from a given surface.

Candela: The unit of luminous intensity emitted in a specific direction by a source equal to one lumen per steradian—the unit of solid angle that, having its vertex in the center of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. (There are four steradians in a sphere.) I used to take steradians, but though they helped me bulk up, I became too edgy.

Lux: The metric unit for mea-suring the amount of light that falls on an object. Lux is the European equivalent of the British footcandle (or lumen).

Lumen: The unit measurement of luminous flux equal to the light emitted in a solid angle by a uniform point source of one candela intensity. So, basically, lux, lumen, footcandle and candela are all pretty much the same thing. But Kelvin is way different.

Kelvin: The unit of absolute temperature used to designate the color temperature of a light source.

Now, let’s clarify daylight/natural light. People think those terms refer to the color of the sun—a warm, yellow light. It is really the blue/white color of the sky.

While daylight, natural light or “full spectrum” light is the perfect type for color matching, it is not so great on skin tone. People want an amber glow that has the feel of firelight. This is really in the range of incandescent light (2,800K). Daylight is 5,000K, a very cold light, like in an operating room.

What customers may really be asking for is color-corrected light, which means that the quality of the illumination comes close to incandescent but is from an alternative source.

Randall Whitehead lighting designer
Randall Whitehead, IALD

Randall Whitehead, IALD, is a professional lighting designer and author. His books include "Residential Lighting, A Practical Guide." Whitehead has worked on projects worldwide, appeared on the Discovery Channel, HGTV and CNN, and he is regular guest on Martha Stewart Living Radio. Visit his website www.randallwhitehead.com for more information on books, upcoming seminars and the latest lighting trends.

Leave A Comment

  • Web page addresses and e-mail addresses turn into links automatically.
  • Allowed HTML tags: <a> <em> <strong> <cite> <code> <ul> <ol> <li> <dl> <dt> <dd>

More information about formatting options

By submitting this form, you accept the Mollom privacy policy.

Latest from ask randall

Yes, using just recessed downlights in a room produces harsh shadows on people’s faces and makes the ceiling feel lower. I would recommend dividing... read full story
As far as indirect lighting goes, using LEDs, I would recommend 250 lumens per foot. Your pendant fixtures should be in the 36-inch to 42-inch... read full story
The short answer is yes, you can get LED that is daylight in color and has full-spectrum quality. I need to put in a qualifier, though. Full-spectrum... read full story
I think what you’re doing is absolutely correct. Use two mirrors and position the three sconces so that they are equidistant on either side of the... read full story

Webinars

Wednesday, June 82 p.m. EDT Register for this free CEU webinar here. Webinar Overview:Learning units:AIA/CES LU (HSW) 1.0 Learning UnitIDCEC (IIDA/ASID/IDC/IDS) 0.1 CEUNKBA 0... read full story
Sponsored by Emerson and Kuzco Lighting. This free CEU webinar has already taken place, but you can still watch it on demand by clicking here. Webinar Overview:Learning units... read full story
Sponsored by Bock Lighting, CSL, Fanimation, Pure Lighting/Edge Lighting and USA LED Lighting Solutions.   Wednesday, June 10, 2-3 p.m. EDT This free CEU webinar has... read full story

RL Tweets!

Email Subscriptions