How can they be so cheap! (CF light bulbs)

[Ian Stirling]

Surprised to find large quantities of "2 for 1" 99p 18W/100W CF bulbs by Philips, in Morrisons. They claim 7000 hours.

[airsmoothed]

I assume these are the same bulbs as were offered a few months back; if so be aware that, based on personal experience, after a few months use the bulbs start taking longer & longer to reach full brightness. I fitted half a dozen at home when the offer last came round, the two most used ones are taking much longer to brighten now. The worst cas eis the bulb in the lounge, which has been switched on for maybe 10 hours per day during the winter months, but only switched on and off a couple of times per day.

[Adrian C]

In my local Morrisons, the entire basket of them is Edison Screw fitting :-(

In ALDI, you can buy Osram's for a quid. I find these light up to specified output quite quickly - the philips take a few tens of seconds longer.

[Chris Bacon]

IME all "CF" lights, the sort that replace incandescent ones, are rubbish. Why does the output drop off so quickly? Why do they take time to brighten fully?

[Ian Stirling]

In my local one, there are two baskets (of equal sizes) with ES and bayonet. I have no idea if there are more in the back.

Over the first minute, just testing, the philips one seemed brightest after about a minute.

[Ian Stirling]

The second one is partially due to reducing the amount of mercury in them.

[Andrew Gabriel]

Also, they are mostly designed to run with a tube wall temperature of 100C, which is quite a bit different from the 20C when you first switch them on. Traditional fluorescents are designed to run with a tube wall temperature of 40C, which is not so different from the initial switch-on temperature, so the initial brightness is not so far off the final brightness.

[Ian Stirling]

Even more so at low ambient temperatures.

[Dave]

How long is 'much longer? I may have a use for them at school if the life of them is good enough.

Dave

[Ian Stirling]

The morrisons ones claim 6700 hours at 3 hours/day.

As with all CF devices, these are around 60lm/W, whereas the best linear tubes are around 100lm/W.

[John]

Just as a side issue, can these low energy CF lamps be used in twin concealed light fitting? The type that have the fitting screwed to the ceilng and a glass dome covering the lamps.

Cheers

John.

[Ian Stirling]

If they physically fit, yes. There may be an issue with them having slightly poorer life, if the fitting is very insulating. Of course, the fitting will run cooler than with ordinary bulbs, but the CF lamps may be hotter than in free air.