MicrobeHunter.com Microscopy Forum

Looking for more information on extending incandescent bulb life by reducing voltage.

Found this in Wiki: https://en.wikipedia.org/wiki/Incandescent_light_bulb

For a supply voltage V near the rated voltage of the lamp:

Light output is approximately proportional to V 3.4
Power consumption is approximately proportional to V 1.6
Lifetime is approximately proportional to V −16
Color temperature is approximately proportional to V 0.42

Anybody have more info or links? A Chart would be nice.

Here's a chart based on a 100v. system you can make . Take graph paper with any sized squares. Pick a section 10 squares wide and 15 squares high, or rule one with arbitrarily 1 cm. squares.
Each square along the bottom is 2v . from 90v. to 110v.
Each square along the side is a percentage of nominal bulb life ; 0 at the bottom and 300 at the top in 20% increments.
Now draw a line from 290% at the left edge with a very gently sagging curve through the intersection of 200% and 95v, then with a slightly increased sag to 100 and 100, a more increased sag to 50% and 105v, which continues on to 30% and 110v.

The arc should just go S.W. of 180 and 96, 140 and 98, a little more S.W. of 80 and 102 and closer to 60 and 104.

Here's a chart based on a 100v. system you can make

:) Not quite what I had in mind, but thanks.

Found a more complete formula:

I don't have a scanner. I'll try to take a good, glare free photo of it and post it. Comes from a scientific bulb catalogue

Lynn wrote:If you scan that photo then it will be more clear. Please try to barrow scanner from someone.

Note the date of the post to which you responded. Lynn

You might, however find Fig. 1 of this useful:
https://www.intl-lighttech.com/specialt ... lled-lamps

MichaelG.

It's not quite as simple as a voltage vs. life chart, while we're bringing an old thread back to life.

The high inrush current to a cold tungsten filament is a major contributor to early failure (and why bulbs often fail when first turned on).

One might ideally always start with the voltage way down, then turned gradually to needed brightness. When not in use for a while, especially at higher levels, turn it down.

PeteM wrote:It's not quite as simple as a voltage vs. life chart, while we're bringing an old thread back to life.

The high inrush current to a cold tungsten filament is a major contributor to early failure (and why bulbs often fail when first turned on).

Very true, Pete ^^^

Back in the good ol' days, some slide projectors were fitted with soft-start circuitry.

MichaelG.
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Edit: ... and a few seconds googling found me this:
https://www.electroschematics.com/8088/ ... gen-lamps/
Note: be sure to read the comments.

The reason Lynn has bumped this old thread with a non helpful/non relevant reply (this is the fourth pointless post) is that he/she/it is a spammer and is only posting to get members to click on the link in the posters signature.

However, since this post will remain 'bumped' and original image hosting service is no longer of use (and I can't remember what the image was) I will post an image of the rerated bulb life formula from an article

Sample is for a Tungsten 60 w 12v bulb with 100 hour rated life

By limiting the applied voltage from 12v to 10v, the working life can be extended from 100 to around 1000 hours.

Note: There is of course a brightness penalty to extending bulb life!

75RR wrote:The reason Lynn has bumped this old thread with a non helpful/non relevant reply (this is the fourth pointless post) is that he/she/it is a spammer and is only posting to get members to click on the link in the posters signature.

Thanks for the 'heads up' ... I was too busy trying to help, to notice the link
... thought I recognised the name, but Lynn must have been lurking here for months.

MichaelG.
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Edit: I have just reported Lynn's post of 01-May-2019

There's an excellent introduction to filament lamps, here:
https://www.alliedelec.com/m/d/04fe4bc2 ... e48b19.pdf

With a useful warning on page 9

NB. Special care should be taken since error can occur due to the exponential nature of the calculation.

MichaelG.