Be Careful When You Shop For Compact Fluorescents
Brian recently wrote that CFL Sales are Plummeting in the US--Right When they Could Help Most, and in the comments to his post there were many complaints about how fast they burned out, how awful they looked, and how long they took to warm up. Recently at IIDEX, a big trade show, I talked to a representative of Standard Lighting about why my expensive PAR spotlight style CFLs took so long to warm up.
He told me that all of the cheap spiral style bulbs were designed to be pointing up in lamps as incandescent replacements, and the heat rises away from the bulb. Put it upside down in a potlight and they overheat the electronics in the base and burn out early. In the design of the spotlight style bulbs, they have to control the heat, which they do with a different amalgam of mercury that takes a lot longer to vaporize but runs a lot cooler. He said that the big mistake everyone makes is thinking that one bulb fits all, whereas just like with incandescents before them, there are dozens, even hundreds, of colours, sizes and permutations.
Important things to look for:Colour Temperature
The bulbs come in different colour temperatures, which are based on the light given off from a piece of metal at a given temperature.
When talking about white light sources we use the description "warm" and "cool." White light with a yellowish tinge (think candlelight and fireplaces) is considered "warm." Incandescent lamps produce a warm white colour. Bluish white (think moonlight on cold snow) is considered "daylight." Fluorescent lamps can produce warm white or daylight (or anywhere in-between) depending on the mix of phosphors used.
It is important to remember that indoor spaces lit to lower light levels will typically look and feel better under warm lamps, while higher light levels are easier to tolerate using cool lighting. A space which receives an abundance of sunlight may seem more natural when cooler lamps are installed since their light is closer to high colour temperature of natural daylight.
A warm white fluorescent is very, very close to the colour temperature of an incandescent bulb. But another factor may be even more important:
Colour Rendering Index (CRI)
The CRI is a rating of the quality of the light on a scale of 0 to 100, with incandescent light bulbs and daylight considered to be 100 because they both have very smooth, even distribution of colours across the spectrum. Daylight and incandescent have very different colour temperatures, but are still considered to have perfect CRIs.
Fluorescent bulbs work by having mixes of phosphors excited by being hit by a mercury molecule and giving off light, and how good they look is a function of how the phosphors are mixed. Cheap bulbs might just have cheap phosphors and have a really spiky balance of colours, and not look very good at all.
The higher the CRI, the more natural the colours appear. Lamps with very good (70-80 CRI) and excellent (80+ CRI) colour rendering properties are accepted as "high quality light" because objects and people will look more appealing and natural.
When you used to go into the hardware store, you were faced with a wide array of different shapes and wattages of bulbs, different ratings for lifetimes, there were dozens, if not hundreds of choices.
When people look at CFLs, they have no frame of reference of a lifetime of bulb shopping and just pick the cheap spirals and stick them everywhere. They don't go in pot lights, they shouldn't go upside down, and they should be chosen according to the specific condition, just like you used to when you bought a spot for a pot and a seven watter for the fridge. It is no more complicated.
If you want an incandescent experience, go for a high CRI and a low colour temperature. If you want the bulb to last its rated life, get one appropriate for the fixture. Try a real lighting store instead of the big box; they will sell you the right one.