Loss due to pearl GLS bulb compared to clear

[Zak]

Is there a rule of thumb for what percentage of light output is lost
by having a pearl finish to the glass compared to having clear glass?

Am thinking of regular GLS bulbs.

Is it of the order of 5% ?

 

[Andrew Gabriel]

Is there a rule of thumb for what percentage of light output is lost
by having a pearl finish to the glass compared to having clear glass?

Am thinking of regular GLS bulbs.

Is it of the order of 5% ?

ISTR the old Thorn Technical Handbook quoted 10% loss for painted
bulbs, such as golf balls and mushrooms. I would have guessed the
etched glass of regular GLS bulbs would be significantly less,
particularly recently where they've become a lot less etched than
they used to be (if it's still etching they use at all -- it's
not very even).

 

[Victor Roberts]

ISTR the old Thorn Technical Handbook quoted 10% loss for painted
bulbs, such as golf balls and mushrooms. I would have guessed the
etched glass of regular GLS bulbs would be significantly less,
particularly recently where they've become a lot less etched than
they used to be (if it's still etching they use at all -- it's
not very even).

I can't comment about GLS in Europe, but the so-called
"frosted" lamps used in the US are usually no longer etched
with hydrofluoric acid. The environmental issues involved
with disposal were too severe, and all or most of the
manufacturers now deposit a thin diffusing coating on the
inside instead of etching the glass with HF.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Victor Roberts]

ISTR the old Thorn Technical Handbook quoted 10% loss for painted
bulbs, such as golf balls and mushrooms. I would have guessed the
etched glass of regular GLS bulbs would be significantly less,
particularly recently where they've become a lot less etched than
they used to be (if it's still etching they use at all -- it's
not very even).

I can't comment about GLS in Europe, but the so-called
"frosted" lamps used in the US are usually no longer etched
with hydrofluoric acid. The environmental issues involved
with disposal were too severe, and all or most of the
manufacturers now deposit a thin diffusing coating on the
inside instead of etching the glass with HF.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

 

[TKM]

Is there a rule of thumb for what percentage of light output is lost
by having a pearl finish to the glass compared to having clear glass?

Am thinking of regular GLS bulbs.

Is it of the order of 5% ?

Your question is particularly interesting because of what the lamp
manufacturers struggled to do over many years to minimize even a fraction of
a percent efficacy loss in their products.

As others have indicated, the traditional method of bulb diffusion or what's
called "inside frost" is done via an acid etch process using hydrofluoric
acid inside the bulb. The process is fast and cheap, but multiple doses are
required to maintain bulb strength and getting rid of the used acid and bulb
rinse water is an environmental nightmare. You can still find inside frost
lamps, but it's unlikely that they were processed in the US or Canada. I
doubt that many are processed in Europe either. An older frost technique is
sand blasting. That works fine for diffusion, but bulb strength is
compromised.

Both sand blasting and acid etch reduce lamp efficacy by less than 1%
compared to a clear glass bulb.

So, coatings, both inside and outside, have become the norm. And you are
right, efficacy losses of 1-5% are typical for white diffusing coatings.

Terry McGowan

P.S. Some of the old incandescent lamp engineers claimed that frosted lamps
were more efficient in some types of fixture optical systems than clear
lamps; so there was actually no loss, but rather a gain, in overall efficacy
with a frost coating. They were vague about the types of optics though, so
maybe someone else can explain that.