A high pressure sodium lamp consumes more energy at...?

[mx10018]

A high pressure sodium lamp consumes more energy a the end of its life cycle??
This is something our supplier is telling us, we think he is only trying to sell more light bulbs.

please advise,
gonzalo

 

[itsmoked]

He may not. As HIDs lose their gas,(through various unstoppable mechanisms), the arc voltage rises.

Power = V x I

This is why old bulbs start blinking off then restriking. It is because as they heat up the required arc voltage goes up until the ballast cannot supply enough voltage and the arc extinguishes.



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rovineye]

There are also some systems that compensate for lower lumen output of aged lamps by increasing input power. I have only heard of this with low pressure sodium tho, and only in installations where consistant illumination levels are required.

 

[jraef]

He is sort of correct, but in a different way than what you related. Lamps are rated in Mean Lumens, the "average" light output at a chosen point in the life cycle based on the Lumen Depreciation factor of the lamp design. For HPS lamps, that measuring point is 50% of the rated life of the lamp. So when your lighting designer chose the type and height of the fixtures and lamps in them, they based everything on the Mean Lumen output of the lamps. As the lamps age, that lumen output is decreasing rapidly. Some ballast systems then attempt to maintain the lumen output by increasing voltage as Keith said, which increases power consumption. If you don't have that kind of ballast, then light output just drops at a steep curve. Either way, the recommended replacement point of the lamps is 70-80% of the rated life at a given burning cycle, based on a trade-off of lumen output loss or increased power consumption.

Keep in mind that you can't just go by the rated life on the packaging of the bulb for this. The burning cycle effects the rated life by virtue of the number of restarts per cycle. If you go 10+ hours between restrikes, there is little effect on the burning cycle. If you go 5 hours between restrikes, the life is reduced by 25% and at 2-1/2 hours the life is reduced by 50%.

JRaef.com
Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[jraef]

Grammatical error correction... "affects the rated life..."

Grrrr... one of my own pet peaves!