Some CFL bulbs that I’ve tired have produced really blue light, which I don’t like; others have given a nice mellow yellow light, which I do like.
Is there a way to tell from the package what type of light they produce? Given the cost, I don’t like trial and error with different brands.
Look for the Kelvin number on the package.
This wiki article does a great job shedding light on the workings of compact fluorescents, including colors, includes side by side comparisons of what some of these bulbs look like when illuminated. Compact fluorescent lamp - Wikipedia
Basically, you’re looking for “soft white” designation which translates to about 2700K.
Home Depot usually has a display where you can see the CFLs they sell operating side-by-side.
What you’re talking about “color temperature”, and others have explained to how to gauge it. That tells you the approximate color of the bulb.
As an interesting aside, I thought I’d mention that in addition to color, there’s a school of thought that says truer “natural” lighting requires full-spectrum lighting: light bulbs that try to emit across as many wavelengths as the Sun does, not just in a visible warm white – for example, they’ll emit some light in the ultraviolet and infrared portions too.
There’s not really regulation on the term, however, and different bulbs will perform differently. I don’t think studies have found any benefit to human health in the bulbs, but some plants might prefer them.
thanks for the replies, everyone - I’ll check it out on the weekend shopping trip.
As it happens, I needed to buy a CFL this weekend. The hardware store had a couple of nice displays showing the difference in light provided by bulbs at different color temperatures. But then the package of two GE “energy saver” CFL bulbs I was looking at didn’t seem to have the color temperature marked on them, which was really frustrating. Even the stock clerk working nearby was only able to find that the part number started with SW, which he suggested meant that they were soft white bulbs.
The colour temperature rating of a CFL is only a poor approximation to the manner in which it approaches natural light. This is because it is a line spectrum emitter. In reality it has no equivalent temperature, and the value given is a fudge that works for comparing the perceived colour of a white (or neutral grey) material. Light sources with wildly different spectra can have the same colour temperature. The perception of coloured materials will always be wrong, and will differ, even with lights that have the same colour temperature. Let alone compared to sunlight, or true thermal light emitters.
The ability of a light source to render the colours of materials well is measured by its Colour Rendering Index. This is quite different to its effective colour temperature. Sources with the same colour temperature can have very differernt CRI values. In general line emission light sources have rotten CRI values.
The full spectrum lighting purveyors do not share a single theory, and there is so much snake oil that it is sadly now mostly rubbish. The original idea was that a light source that was as close to sunlight in colour perception was a good thing. Nothing wrong with that. Some idiots decided that this meant that you had to have the invisible wavelengths too - for no good reason - mostly by not understanding colour perception, and probably adding some psuedo-science. So you get idiots pushing lamps that, if they actually worked as advertised, would be dangerous, emitting lots of near UV. There are also purveyors of supposedly wide spectrum CFLs. However despite their charging ten times the price of a conventional CFL, the actual emission spectrum appears indistinguishable from a tri-phosphor CFL. So close that one might be forgiven from believing that they simply repackage them.
Interesting. Two questions, if I may.
So how DO you shop for bulbs with a good CRI? How does a normal person even find this data? And is there a particular bulb technology that does this well?
You say “the perception of colored materials will always be wrong”. With CFLs quickly becoming the norm, would they become the de facto correctness for color? What would you compare them to see a colored object’s “truer” color? Sunlight?
From a visual standpoint the Color Rendering Index scale may not be the best choice to use for selecting light bulb colors.
CRI:
This chart display shows several artificial lighting examples, and how they appear according to their K (kelvin) numbers. And again, this is about shopping for lightbulbs - am not questioning the science info offered by Francis Vaughan.
lighting chart
Also important is efficiency, lumens-per-watt, which is how much light you get for how much electricity the bulb uses. You should be getting somewhere around 65 lumens-per-watt (at least initially- in other words when the bulb is new). For example this 26w CFL GE helical I have here is labeled “soft white” (which I happen to know is 2700K because I looked it up at GE website) and is rated at 1700 lumens. Which works out to be 65.38 per watt.
In a nutshell:
For the traditional tungsten-filament glow of the old fashioned incandescent bulb, look for “soft white” or “warm white” name designations, or 2700K.
If you prefer more the traditional “cool white” fluorescent look, then 4000K-4100K
A bit more blueish white, look for 5000K, (or even slightly more blueish 5500K)
If you want even more blueish white - like the color of the HID lamps on Cadillacs and some of the pricier cars out there - look for CFL’s that are 6500K.
Unfortunately, that chart is pretty useless on a monitor–unless you have it properly profiled for color matching, which is something most non-graphics-artists usually don’t bother to do. Monitors have their own color temperature settings and are not exactly the same even within the same model.