Wednesday, 30 May 2018

My Lumens are Hot

When I was a university student, I was a server at a prominent steak house. They set the mood by using dimmed lighting and the lighting was very "warm", bulbs that emitted more red and orange light. They told us it was intended to make people feel more relaxed, romantic and even look better. The warm colored bulbs make your skin look more natural and radiant.

You just bought a new pendent fixture from Stride Lighting with the purpose of creating a similar atmosphere in your dining room. What bulbs should you buy?

Well your choices are basically Halogen, CFL, LED or the retro Edison bulbs. Printed on the majority of light bulb packages are two numbers to help you decide: Lumen rating (light output) and Color Temperature. So lets take a look at how these two numbers will help you set up your lighting to give you the best end result.

Lumens are simply a universal way of comparing different lighting sources on an a even playing field. Prior to the need to be energy efficient in our society, light bulbs were sold based on their wattage, or total power consumption. More wattage meant a brighter light source. However with the rise of new technology (CFL and LED) that is no longer the case. Greater wattage does not equal greater light output (see our previous posts, No Love for Tungsten, and CFL Bulbs Explained for why they differ in efficiency). You can produce a brighter bulb with less wattage. That's where lumens come into play. Simply put lumens are the SI (Système international) unit of a measure of the perceived visible light emitted from a light source.  

Now, many people want to know how many watts are equal to a lumen. 

Well unfortunately that's not a question that can be answered. Watts and lumens are a measure of different quantities, energy consumed vs. emitted light. So for a LED vs. an incandescent light bulb it varies, 100 lumens/watt compared to 10-15 lumens/watt respectively. 

So what many manufactures do is simply compare a new product to an old product. A 100 W incandescent bulb. For example, a certain 26 watt CFL bulb may be equal to a 100 W light bulb, or they could simply give you the lumen rating ~1600 lumens. The lumen rating is a more accurate rating than a generalized comparison. 

Your basic goal is to find the correct brightness to meet your needs with the lowest wattage possible. Biggest bang for the lowest buck. However brightness is not color. This is where color temperature comes into the mix.

Color temperature is used similarly to lumens as an attempt to inform customers what they can expect when they buy that product. 

So you purchase  26 watt CFL bulb and the package says 6400 K on the front, what does that mean? 

This is the color temperature rating. The K value is a temperature measured in Kelvin, used primarily in the scientific community. As a reference point, the freezing point of water is 273 K. The number, or temperature, is used to indicate what color the bulb will glow/emit when operating. This is referenced to the color a black body object, see No Love for Tungsten, will emit when it is at a specific temperature. So the higher color temperature number, the more "cool" or blue the light produced will appear. The lower the color temperature, the "warmer" or more red the the light produced will appear. Daylight falls right around 6500 K with a standard incandescent light bulb closer to 2400 K, an open flame below 1900 K. Color emission starts at the red end of the rainbow and builds with temperature to the blues/violets.

Hence why cooler is warmer color and why hotter is a colder color. Color temperature values refers to the perceived colors emitted from the bulb (not necessarily the lumens, they are independent. You can have a high lumen but warm colored light). 

So how does this tie into your dinning room or any other location?

Consider what are the needs of the room you are placing this fixture in. If it is to be a relaxing, cozy area (living room, dinning room, bedrooms), look for bulbs in the lower K range. If you are needing good lighting to do work (kitchen, work shop) then perhaps on the upper end closer to a day light rating (6500 K). 

Keep in mind, different bulb designs have natural limitations. CFL bulbs may have similar color temperature rating however they are not equal with the actual light they are producing.

An LED 2700 K bulb vs a CFL 2700 K bulb may look similar in color but due to how they produce light ( see CFL Bulbs Explained)  CFL bulbs do not always produce a complete spectrum (rainbow) of light. Here you can see, this LED bulb produces true white light with a complete light spectrum (A diffraction gradient and a spectroscope where placed in front of the camera lens to capture the light spectrum).
However a comparable CFL bulb is missing the yellow portion of the light spectrum. Even though your eyes may perceive the bulbs to be similar they will create poorer light quality. 
That makes CFL bulbs a poor choice for art studios and bathrooms as the incomplete light spectrum tends to be unflattering. Incandescent/halogen bulbs will always produce a complete warm light. LED's are being manufactured that function across a broader color temperature spectrum as they can be manufactured to meet that specific demand. More to come on LED's.

I hope this helps you on your next shopping trip to pick the appropriate bulb for your design needs. 

Thanks for stopping by! 

Any questions don't hesitate to ask. Join us on Facebook @  facebook.com/groups/stridelighting/ to join in on more helpful information, support and discussion on home lighting. 

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