What is a phosphor

[gar]

171223-1200 EST

What is a phosphor? They are used in many different products, and are becoming our major source of visible light. Usually ultra-violet light is used to excite the phosphor.

In fluorescents the UV is primarily from mercury. In LED light bulbs from UV emitting LEDs.

See https://en.wikipedia.org/wiki/Phosphor

Chemical composition and mixtures of different phosphors determines color.

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[junkhound]

Have noticed you are a scope guy from other posts. Do you recall (or are you old enough?) the 'bad old days' when the phosphors in 'fast' scopes were so sensitive if you left the intensity to high for over a few minutes on a repetitive waveform you burnt the phosphor and had a 'storage scope' :lol:

Pop bought me a $160 EICO scope kit for Christmas circa 1957 (a weeks wages back then!) and it had a sensitive phosphor CRT. All of 100 kHz BW.

Nowadays one can buy a 15 YO 4 channel 500 MHz digital scope for less than $160 (just a few hours wages). I lowball bid on a few scopes a month for a few years and got a TEK 420A for $120! Some stuff is cheaper now!

I do wonder if fluorescents will be sold much longer as fast as LED prices are dropping.

 

[gar]

171224-1254 EST

junkhound:

Thinking about fluorescent efficiency of the T8 I believe it is primarily a result of finding more efficient phosphors, and probably more expensive.

UV power density at the phosphor coating is about the same between T12 and T8. Power input ratio is 40/32 = 1.25, surface are ratio is 1.25/1 = 1.25 .

There is also a peripheral advantage in that the T8 obscures only about 80% of reflected light that a T12 obscures.

My first chance to play with a scope was around 1945 and it was a 3" Du Mont. In 1949 I built a 5" scope from a WWII surplus 5BP1, several dollars, a new 2000 V transformer, and some other new parts, and misc other parts.

I went onboard BB-64, USS Wisconsin, a few days after it came out of mothballs, 5 Jan 1951 in Portsmouth, VA. Probably not more than about 10 of us then. Shortly afterwards we got a new triggered scope. Smaller than 5", but not 3". Later in 1952 when I was in a lab at the Brooklyn Naval Shipyard I had my first exposure to Tektronix scopes.

On a CRT scope one could never leave the beam on one spot continuously or the phosphor would be burned, as you said.

I still like analog scopes, but none of my Tek scopes work.

There are clearly things I can do with a digital scope that are not possible with an analog scope.

I have a long history with fluorescent lights and it has been relatively good. My failing T12s will likely get converted to T8s with new ballasts. Many of my old ballasts have failed or are failing. But clearly LEDs are better outside (cold weather).

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[junkhound]

around 1945 and it was a 3" Du Mont

dang, you ARE and old cuss


There are clearly things I can do with a digital scope that are not possible with an analog scope.

Had a chance to work with any of the more recent (7-8 years and newer) TEK scopes that are windows based ?

Can do wonders finding intermittent problems, set it up for 5 GHz sample rate, let it record for minutes, pick out that 10 ns transient from the digital memory.

etc.

 

[Sahib]

171223-1200 EST



Chemical composition and mixtures of different phosphors determines color.

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It also determines lamp efficiency and life:T8 lamps with triphosphor coating.

 

[hbiss]

I still like analog scopes, but none of my Tek scopes work.

Why is that? I went to use my 2235 a few months ago only to find that the sweep wasn't working. :rant: Tek was supposed to be the best. :?

I built a 3" back in the 60's.

-Hal

 

[gar]

171225-2453 EST

hbiss:

Analog scopes have the direction of rotation of knobs correct (correct because I grew up with those directions). Clearly the analog designers did not have much input on the digital scopes.

Image intensity on an analog scope can give me information that I may not get on a digital scope, or I have to use some other means to get what I need to know.

However, a digital can do things for me that no way could I do on an analog. In most ways the digital will be better.

In recent years I don't think Tek is what it used to be. I don't have a LeCroy, but I am impressed with demos. One has to work with a scope on different problems to get to know what it can do and how to used it to do what you need to do.

How well did your homemade 3" work, and does it still work?

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[retirede]

I built a 3" back in the 60's.

-Hal

This triggers some memories. I once followed instructions in Popular Electronics magazine back in the '70s to convert an old television into a scope. It had no real practical use (no calibration possible, non-linear frequency response, no triggered sweep....) but the exercise was during my formative years and one of a series of steps that eventually lead to my career path.

 

[hbiss]

How well did your homemade 3" work, and does it still work?

Good enough for audio work which is what I did at the time. Sadly it's long gone but I did re-purpose the Bud cabinet with the handle on top to house a 12v/10a regulated power supply. It uses a 709 op amp and it works great to this day.

-Hal