Candy Questions in Tech 8

(Assuming a 120v/60Hz American lighting package) Note: review last questions posting about the effects of voltage on a lamp.

 

I had to vote for Lobby... cuz its such a funny word, i never heard it before

 

Perhaps you'd know it as a foyer? I think that's an even funnier word for the same thing

The S4 fixture is a "red herring" - regardless of the fixture it's mounted in, a lamp rated for 575 watts at 240 volts is only going to get 143 watts at 120 volts. It'll be pretty dim and shifted way toward the red end of the spectrum - okay for a sunset, or maybe a fire effect, but not much good for anything else.

John

 

YEP.... Foyer is what its called here... there aint nothin funny about that.... cept when "posh" people call it the foyae!

 

DMX tools, you get it - gold star for you. A bit early to post an answer on the question, I would prefer to refrain from answering survey questions until at least 10 people have voted - my overall goal for candy questions yet to be reached I think. But anyway, you understood the depth of the question and surmised the best use for the lamp. Sunset would be another good use for it but with the amber shift, it would be hard to control what you get should you need to add gel or wish to design the look. On the other hand, the amber color temperature would linger quite a while which could be of interest. The most simple use for it however is still Lobby lighting where in this case it would be a lamp that would last almost indefinately (9,762.7 hours at 118v) and the amber color coming off it would not be that large of a concern. As for 143 Watts, nope it's still doing 575 Watts/resistance worth of work, just at a much lower pressure - voltage. What you would mean is (and not checking your math) about 143 Watts worth of light or Lumens in comparison to a 575w fixture. Interesting figure the 143, how did you come up with it? Seems a simple way of figuring output.



The concept/lesson in the candy question is a recognition that the voltage rating on a lamp as compared to the actual line voltage of your system plays a factor in how much output it's going to have, or what color temperature it will appear to be no matter what the specification is. Find a box of 130v PAR 64 lamps in the store room and install them as replacements next to the 120v PAR 64 lamps and they are going to be dim in comparison to other lamps in use of the same wattage.

 

Figuring it out - watts = volts x amps. Amps = volts/ohms. If the resistance is fixed (ohms) then half the volts will cause half the amps. Half the volts times half the amps is one quarter of the watts, and that's not just in terms of light output, but in terms of how fast the electric meter goes 'round and 'round as well. One quarter of 575 is 143.75 - I probably should have rounded up to 144 instead of just truncating, but what's a watt or two among friends...

John

 

That math can be pretty useful. Extending use of the formulas I just mentioned - how many of those same lamps can you safely run on a 120 volt 20 amp circuit breaker?

We already figured out that each lamp is actually going to use about 144 Watts at 120 Volts. We can transpose the equation from (Watts = Volts x Amps) to (Amps = Watts / volts). 144/120 = 1.2 - each lamp will draw 1.2 Amps. 16 lamps on the same circuit will draw 19.2 Amps - fairly safe, though as a rule of thumb, I don't like to come that close. 17 lamps will draw 20.4 amps, a slight overload - the breaker will pop, but it'll probably take a while (several minutes to several hours, depending on the particular breaker).

There is another way, just as valid. Figure out how many total watts the breaker can handle. Watts = Volts X Amps: 120 volts times 20 amps = 2400 Watts. Each lamp will use 144 Watts so 2400/144 = 16.67: sixteen and two thirds lamps. I have yet to find a dealer that will sell me 2/3 of a lamp, so we'll just say 16 lamps to make it easier. :wink:

Anyone care to try it for 90W 120V halogen PAR38's and a 15 Amp breaker?

John

 

AAAAAAHHHHHHH
PHYSICS!!!!!!!
well, i still gotta know it for the midterm...

 

Yes, Physics! and Algebra! But isn't it a little easier to learn and remember when you have a practical application? Knowing how many lights you can plug into one breaker or run off one dimmer can keep that breaker from popping or that dimmer pack from smoking in the middle of a show - a VERY practical application.

A good grade on the midterm is a "nice to have." Keeping the lights working for the entire performance is a necessity.

John

 

Agread.

before my time at my current school I heard that they compleatly overloaded the entire system, and it all started sparking!!!!!

if only they paid attention during physics class...

of corse, it could have also been because they used actors to run the lights and sounds, so none of them really knew what they were doing (not that I have a much better idea mind you...just a little...)

anyway, yea, deffintly. Now why don't teachers understand that making the set look amazing or running lights, cables or sound cues is a good excuse for not having your homework...

 

Oooohhh...Ok, I assumed my 220V

 

I am one of two reisdent geniuses in a little town called brigham city utah- one day they called us over to the middle school for 8-9 grade kids to fix a dimmer problem, so we go check their hard patch-(they still have one) and they have 6000 watts on a 1k watt dimmer! their excuse is-the janitors did it- small wonder the started a fire during a show... :roll:

 

Funny--I just looked in on this question (I know, a bit late for points) but when I first read it, I was thinking it was a trick question since when I do lighting work in Europe, those lamps work quite well for gobos and pattern projectors. I also was in a venue in St. Louis where there was no available neutral in a 3 phase system, and someone had the bright idea to put in a 3 phase dimmer and relamp to 220 lamps (all from Europe). Seems like it would have been easier to run a neutral or put in a transformer--but hey, maybe they had some source overseas.

So, I thought "Never Assume".

BTW, what do you call a 77v HPL 575 which some well meaning soul overrode the pin and used at 120v? Answer: A $20 squib. (That is one very expensive photoflash effect. It only took 3 lamps before the techie realized they sent the wrong lamps.)

 

$20.00 Squib!!! I like that, I'm going to have to start replacing my going super nova equasion with squib. Thanks.

 

brilliant!

 

Well, one my "classic" stories go back to my first show in High School. I was doing special FX, and my Head was giving the lighting guys a hand, so he was checking Par64 (we use them in series remember) so he would plug one in, have a flash and say, "It Works". It took 6 of them before someone realised it and stopped him...so much for a Head of department!

 

This would be great for use with a gobo with the S4 having a built in gobo slot and the brightness of the light would make such a great bright pattern

 

I think you were thinking of this lamp in the reverse direction. As rated voltage of a lamp goes up, life goes up but output and color temperature goes down.

Actually it would with this lamp make one of the worst pattern projectors around on a 115v system. We are talking about 1,983 lumens at 2560°K color temperature and last in the range of 230,000 hours of life.

At 240v, this lamp should provide 3,200°K 14,900 Lumens 400 hours life. A Normal high output 575w/115v lamp should be 3,250°K 16,520 Lumens 300 hours.


A tallow candle produces 414.81Lumens at 1,400 Calories - how ever that equates to Kelvin. In other words, something like five candles in brightness.

Or, this 240v lamp is about as bright as a 135w incandescent A-lamp with that output (1,750 to 2,135 Lumens) and color temperature in the 2,500°K range, except that the HPL lamp would almost never burn out. There might also be some problems with filament notching and the halogen effect taking place.

Overall this might make an adiquate lobby light because for all intensive purposes you now have a 135w incandescent PAR lamp to shine on what you desire, but you would never see the beam of light otherwise on stage in comparison to other fixtures much less in projecting patterns. That's even before the law of squares was figured into the equasion which would drop it's intensity much further yet.

 

But I just do not understand why you would waste an insturment like this on a lobby display or whatever. Why not find a use for it on the stage instead of wasting it on the lobby when you have other comparable insturments that are easy to use in a lobby. It may not be the best light for a gobo but what really is

 

The availabilty or not of equipment was not a factor in the poll. You found a lamp and it was assumed you had a fixture available to use it with. It's a decent pattern projector especially with a donut. But the question was what good the lamp would be.

By the way, it's been a long time - there abouts of 20 years since algebra x/y type factors. Someone should check my math. I would be interested to confirm the math on what it's going to look like.