Why do "specialty"-shaped compact fluorescent bulbs take longer to come to full brightness than CFL bulbs in the more standard helical shape?

January 27, 2009 4:05 PM

Why do "specialty"-shaped compact fluorescent bulbs take longer to come to full brightness than CFL bulbs in the more standard helical shape?

Having recently moved into a new house, I bought two different kinds of n:vision 14 Watt compact fluorescent light bulbs. One kind starts out quite bright when turned on, but the other is quite dim when it turns on and takes 30-90 seconds to reach full brightness.

The bulbs that brighten quickly are the standard CFL bulbs that are in the shape of a helix. The specific bulb I'm referring to is this one.

The bulbs that take longer to get bright are these A19-shaped bulbs.

From examining them, it appears to me that the A19 shaped bulbs are simply the regular type of bulb with a plastic shell around them. But if this were the case, I don't see why the A19 bulbs would take longer to reach full brightness.

I bought four of each type of bulb and the same thing happens with all eight. I know that colder temperatures can make CFL bulbs take longer to brighten up, but none of these bulbs are in a warmer place than any of the others.

For what it's worth, I have also noticed that globe shaped CFL bulbs at others' houses seem to take longer to get bright than regular CFL bulbs although I don't know what brand/etc those were.

Any ideas?

posted by Juffo-Wup to technology (7 comments total)

Because it takes longer to ionize the gas inside the bulb.
posted by Pants! at 4:23 PM on January 27

Those specialty shaped bulbs just have a regular helical (or other convoluted shape) bulb inside them.
posted by zsazsa at 4:34 PM on January 27

I believe it has to do with the built-in "ballast" circuitry. The cheaper bulbs tend to not turn on immediately (slight delay) and require a brief warm up period, which is a difference in the ballast, I think.

A bit off topic, regarding larger more conventional fluorescent lighting and ballasts: Our main lighting fixture in our "new" kitchen stopped working abruptly recently. I figured a little tiny, 89 cent component called a ballast needed an easy replacement. Well, I was sort of right - the ballast needed replacing, but ballast technology has changed quite a bit since I was a kid. This ballast was a black box that weighed about six pounds and cost well over 89 cents and included many heavy gauge wires to cut and splice. It was quite a chore. But, apparently the benefit of modern electronic ballasts are instant-on fluorescent lights. Live and learn.
posted by ae4rv at 4:35 PM on January 27

Two opposing design factors come together: the enclosed CFs tend to have tighter turns in the internal tube, which leads to a slightly higher firing voltage. At the same time, the tube itself is shorter, which leads to a requirement for lower current.

The 'ballast' circuitry has to balance these, as well as the sudden drop in resistance (leading to lower tube voltage & higher tube current) when the tube fires. They seem to do this by limiting the current and ramping up the tube voltage in order to strike it (once it's struck the voltage is reduced), waiting a while to allow all the gas in the inside corners of the sharp turns to ionise, then slowly ramping up the current over the next 60~90 seconds until maximum brightness is obtained.

Better designs have more complex ballasts which reduces this, but it's still quite evident. It's a fact of life with all gas-discharge lamps to one degree or another - it's less evident with neons as the strike voltage & hold current is lower and the actinic-ness (to coin a word) of the light reduces the visible effect, and almost non-existant in standard fluorescent tubes because they're straight and have much simpler ballasts. It's most evident in certain U-shaped gas discharge street lights, which can take minutes to get to full brightness because of the curved tube and simple ballast.
posted by Pinback at 5:26 PM on January 27 [4 favorites has favorites]

Notice that your "quicker" bulbs have a longer expected life than your "slower" bulbs (9 years vs. 7 years). That also suggests some difference in the way the two bulbs were engineered.
posted by fantabulous timewaster at 6:05 PM on January 27 [1 favorite has favorites]

Great answers Pinback and fantabulous timewaster, thanks! I had not realized that the bulbs had different expected lives. Once you pointed that out, I noticed that the enclosed bulb is rated at 800 lumens and the non-enclosed is rated at 900, so clearly the bulb/tube itself is designed differently as Pinback mentioned.

I wonder if there is an enclosed CFL form factor that is big enough to accommodate a tube of the same design as a non-enclosed 14W tube. Maybe an A21...
posted by Juffo-Wup at 7:03 PM on January 27

To follow up, I bought some Philips brand 14W A19 bulbs at Meijer and did a side-by-side test between them and the n:vision bulbs. The Philips bulbs started out brighter and warmed up to full brightness noticeably faster than the others.

I was pleased and surprised at this; I didn't think there would be much difference.
posted by Juffo-Wup at 8:47 AM on January 29 [1 favorite has favorites]