Waveform of a 750W Mercury Vapor Bulb

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gar

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Location
Ann Arbor, Michigan
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EE
181107-2222 EST

SG-1:

I expected that you were thinking of was what is ordinarily called a ballast, but I wanted to make clear to others reading this that current limiting is what is important.

I kept my measurements very short to avoid heating the arc tube and its gas/mercury mixture. When heating gets sufficient the arc voltage drop will greatly increase.

When I started the experiment one bulb terminal was connected to 120 V neutral, and the other terminal to one end of the Ohmite resistor. The other Ohmite terminal connected to 120 V hot. These connections only occurred when the AC plug was inserted into the AC outlet for a moment. Not over a second or so.

My scope was AC powered via a 2 prong to 3 prong adapter to float the scope common. Scope common was connected to the connection between the bulb and the Ohmite. One channel measured the resistor drop, for current, and the other the bulb voltage drop. This worked well but I saw oscillation on the bulb voltage drop during conduction. Also the resistor drop showed the oscillation. It was not clear if this was a result of floating the scope common or not.

Therefore I change to connecting the scope common to the AC neutral, using the voltage probe to measure bulb voltage drop, and using a Hall current probe to measure current. The oscillation remained.

I have not experimented with interchanging the bulb leads to see if the + and - arc voltage drop difference moves with the interchange. I expect it will. I expect it relates to where the starter electrode is located since there is only one. Or possibly some other geometry is the cause. I did not make any effort to reduce lead inductance.

See https://en.wikipedia.org/wiki/Gas-discharge_lamp for the color of various gases. The orange might imply neon.

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gar

Senior Member
Location
Ann Arbor, Michigan
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EE
181107-2359 EST

SG-1:

For you to experiment with a bulb that has no internal ballast my suggestion is to initially use a standard ballast for that bulb. After bulb is at full brightness get arc voltage and peak current measurements. Then, if you want to play with a resistive ballast you can calculate a suitable resistor to use.

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mbrooke

mbrooke

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gar said:
181107-2359 EST

SG-1:

For you to experiment with a bulb that has no internal ballast my suggestion is to initially use a standard ballast for that bulb. After bulb is at full brightness get arc voltage and peak current measurements. Then, if you want to play with a resistive ballast you can calculate a suitable resistor to use.

.
Click to expand...

Did some digging and found this thread on the net. Might be of some use:


https://www.lighting-gallery.net/index.php?topic=6847.0
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
181108-1140 EST

SG-1:

Have you switched from a midnight to a day shift?

I have done a little more with continuous power to the bulb. Now using a Variac to get slightly higher voltage and thus current. Input voltage is now about 148.

As the bulb warms up the arc voltage drop gradualy rises, and peak current lowers. After a long time my arc drop is about 50 V and peak current about 2.3 A. + and - waveform symmetry is pretty good.

The negative resistance characteristic of the arc can be seen.

It is clear that the heated electrodes from the arc are at a temperature to produce thermionic emission compared to high field emission when the bulb was first turned on.

..
 
SG-1

SG-1

Senior Member
Location
Ware Shoals, South Carolina
gar said:
181108-1140 EST

SG-1:

Have you switched from a midnight to a day shift?

I have done a little more with continuous power to the bulb. Now using a Variac to get slightly higher voltage and thus current. Input voltage is now about 148.

As the bulb warms up the arc voltage drop gradualy rises, and peak current lowers. After a long time my arc drop is about 50 V and peak current about 2.3 A. + and - waveform symmetry is pretty good.

The negative resistance characteristic of the arc can be seen.

It is clear that the heated electrodes from the arc are at a temperature to produce thermionic emission compared to high field emission when the bulb was first turned on.

..
Click to expand...

Still work evenings, just been on & off vacation lately.

Priced a standard ballast today, over $100. Since I was going to repair a HID fixture, I am going to turn my attention to the LED replacement. It will be next week before I decide on a bulb. Looking at 4000LM or better. Before it goes into service, I will post a waveform.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
181109-2355 EST

SG-1:

You might put out a request on this forum for a fixture including a good ballast that someone is removing because the customer wants to go LED.

I have not been impressed with street lighting in our town where LEDs are replacing gas discharge lights. Nor at my son's building where he is starting to replace failed gas discharge with LEDs in the parking lot. I don't like the color or light distribution of the LEDs.

.
 
SG-1

SG-1

Senior Member
Location
Ware Shoals, South Carolina
gar said:
181109-2355 EST

SG-1:

You might put out a request on this forum for a fixture including a good ballast that someone is removing because the customer wants to go LED.

I have not been impressed with street lighting in our town where LEDs are replacing gas discharge lights. Nor at my son's building where he is starting to replace failed gas discharge with LEDs in the parking lot. I don't like the color or light distribution of the LEDs.

.
Click to expand...

I recently replaced the bathroom light, two tube fluorescent that would not work when it rained, with flat panel 4000LM, 4000K dimmable LED. So far, I should have done this years ago. At night or on rainy days we turn the output down. I do not know about the HID replacements, but with home lighting you can get the temperature that you want.
 
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GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
gar said:
181109-2355 EST

SG-1:

You might put out a request on this forum for a fixture including a good ballast that someone is removing because the customer wants to go LED.

I have not been impressed with street lighting in our town where LEDs are replacing gas discharge lights. Nor at my son's building where he is starting to replace failed gas discharge with LEDs in the parking lot. I don't like the color or light distribution of the LEDs.

.
Click to expand...
If you do not like the color, then lobby for warmer CCT or better color rendering (CRI).
Part of what you see installed is the result of pursuit of highest perceived lumens per watt regardless of color quality.

Sent from my XT1585 using Tapatalk
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
181110-1912 EST

GoldDigger:

I agree, but I get nowhere with my politicians. We have hybrid busses running around town with virtually no passengers. Also these busses are apparently more costly over their lifecycle than plain diesels.

.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
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EE
181111-0752 EST

One hundred years ago today at the 11th hour, of the 11th day, and the 11th month, the shells stopped flying. Big Bertha (17") was still firing until that time. From what my dad had said about this gun I thought it was more like 20".

Back to this thread.

It is interesting to see how the current vs time wave shape changes within 1/2 cycle as a mercury vapor bulb warms up. This is a result of the change in internal temperature, gas pressure, and thus rate of recombination of electrons and ions.

At some point I would like to show these curves, but at the present I don't want to spend the time on this. Possibly someone else will.

Note: voltage drop across an arc, for fixed geometry, increases as pressure rises.

.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
gar said:
181109-2355 EST
I have not been impressed with street lighting in our town where LEDs are replacing gas discharge lights. Nor at my son's building where he is starting to replace failed gas discharge with LEDs in the parking lot. I don't like the color or light distribution of the LEDs.
Click to expand...

I find that I really like some LEDs and really dislike others.

A point made by one of the other members is that white LEDs are generally 'fluorescent', and the light quality will depend heavily on phosphor selection.

-Jon
 
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