18-06-2011, 03:54 PM
Power-cycling and life expectancy: indeed, Jamie, that is a valid point.
I'm not too sure about the filament material in this particular bulb, but basic Physics tells us that the resistance of most conductors increases when they get hot - ignoring Thermistors, for the time being. So when the filament is cold, the resistance is low, the bulb is switched on, there is a surge of current, the filament gets hot & glows, the resistance increases, the current drops. I suspect that the lower the rate of rise of current, the longer the bulb will last - simply because under those conditions, the filament is under less dynamic electrical & mechanical stress.
In a parallel vein, when I used to be a Field Service Computer Equipment Technician, I used to look after about several hundred VDUs at one particular site. Some of these did a daily rota of 'on' for 8 hours, 'off' for 16. However, a few were switched on 24 / 7 / 365. Piece and part of my job was to write monthly reports on Service Calls, etc. One of the statistics I was required to deliver was MTBF. The 'daily use' terminals returned an average figure of about 15,000 hours; the 'always on' units figure was in excess of 200,000 hours! I hardly ever saw those - and when I did, the 'reported fault' was nearly always a fault in a piece of kit that was external to the VDU, but to the non-technical user it looked like a VDU failure. The most commonest (valid) call was simply to replace worn-out CRTs!
Al.
I'm not too sure about the filament material in this particular bulb, but basic Physics tells us that the resistance of most conductors increases when they get hot - ignoring Thermistors, for the time being. So when the filament is cold, the resistance is low, the bulb is switched on, there is a surge of current, the filament gets hot & glows, the resistance increases, the current drops. I suspect that the lower the rate of rise of current, the longer the bulb will last - simply because under those conditions, the filament is under less dynamic electrical & mechanical stress.
In a parallel vein, when I used to be a Field Service Computer Equipment Technician, I used to look after about several hundred VDUs at one particular site. Some of these did a daily rota of 'on' for 8 hours, 'off' for 16. However, a few were switched on 24 / 7 / 365. Piece and part of my job was to write monthly reports on Service Calls, etc. One of the statistics I was required to deliver was MTBF. The 'daily use' terminals returned an average figure of about 15,000 hours; the 'always on' units figure was in excess of 200,000 hours! I hardly ever saw those - and when I did, the 'reported fault' was nearly always a fault in a piece of kit that was external to the VDU, but to the non-technical user it looked like a VDU failure. The most commonest (valid) call was simply to replace worn-out CRTs!
Al.
