Discharge/HRI Lamps

[StageTech620]

Hello! I'm beginning to look into moving heads. From what I can tell, the choice is between LED and HMI. I have a few questions. Is an HMI lamp brighter than a lamp in a source 4 fixture? Also, I've seen that with LEDs, you can print gobos on transparency paper. Does this work with HMI? Or do HMI lamps produce heat?

Thanks.

 

[DELO72]

Hi,

First, let me help clarify the terms. You seem to be all over the place. What you are really trying to decide between is LED and Metal Halide (High Intensity Discharge lamps). HMI/HRI/MSR/CSR, etc. are all just brand terms and acronyms for a TYPE or family of Metal Halide lamps.

Yes. Metal Halide lamps are MUCH brighter than a Tungsten Halogen Filament lamp at equal wattage. For instance-- a 575W HMI lamp puts out roughly 52,000 lumens. A 575W Tungsten Halogen lamp is ~15,500 on average (Between 14,000-16,250). So.. ~4x brighter. This is because the efficacy of HID can be as much as 100 lumens per watt, and tungsten Halogen caps off at around 27 lumens per watt.

HID lamps produce a LOT of heat. Very similar to Halogen lamps in that regard. Since they are more efficient, they convert more of their energy to light than to heat, but they still generate a great deal of heat.

LEDs are increasing in efficacy with every passing day, so they are starting to get there. For high performance fixtures they are in the 80+ LPW range at the moment, maybe even higher. Some prototype LED lamps have been made that achieve almost 230 LPW, but these aren't in a small enough form factor for using in a moving light.

Typically when deciding between LED moving lights and HID moving lights, the real value/selling factor is in the maintenance, not the energy savings. With HID fixtures, every 500-1000 hrs. (in most cases) you'll need to replace the lamp as the quartz begins to divitrify (re-crystalize) and becomes cloudy, allowing less light out. LEDs will also degrade and shift in color and output over time due to the heat, but should operate for far greater periods without needing replacement. So that is the value. If you need highest output, go with Metal halide. If you need least amount of maintenance, go with LED. This is a VERY simplistic way of framing this, and there are a lot of other factors at play. I'm just trying to give a very basic overview and not cover every possible scenario.

 

[StageTech620]

So a 200 or 300w HID Lamp equals what wattage in like Source 4 terms?

 

[RickR]

Your best bet is to read the data sheet for the fixtures themselves. This goes double for mover! Some manufacturers simply put better glass and reflectors into their products, or just a better design overall. Some will even list 'total lumens' rather than 'center beam' lumens.

Look carefully at beam angle and field angle measurements. (highlighting is links to a glossary) They can tell you a lot about how even and how wide a beam the light has. For a profile or beam type fixture beam and field angles should be nearly identical.

 

[JD]

You must also look at the optical efficiency of the fixture. (How much light the lamp puts out actually makes it out of the fixture.) With followspots, Metal Halide blows away incandescent/halogen lamps not only because of the lamp efficiency, but also because MH lamps are more of a "point source" of light, allowing reflectors and optics to be more efficient. The same is true with moving lights, which are also use "projector" optics. LEDs are also more of a point source lamp (or chip as the case may be.) This is why some LED moving fixtures have darn good outputs for the low wattage they draw.

Bottom line, LEDs have a ways to go before they can compete with MH, at least at a reasonable cost. As far as direct comparison of numbers, you have to go to the charts and see what each fixture can give you at a specific distance.

 

[MikeJ]

Seat of the pants punch,
250w hid, is brighter than a 575 S4, Okay starting point, but modern and inexpensive LED fixture have this beat recently.
575w HID, is the minimum to compete in a 120k rig. R2 Wash/spot, Aura, and other 200-300w led fixture are similar.
1000-1600w is the standard for big moving lights. Get ready for LEDs to move in on this territory in the next year or two.

 

[MikeJ]

Like JD said, do research. A MAC 250 was a really bright fixture for its size, and a MAC 500, was a really dim fixture. The Viper has comparable or better output to other lights drawing 200w less. There are always a lot of variables.

you have to consider wash/spot/beam angle distance etc. Sharpys and other beams are only about 200w but in such a focused beam they are incredibly bright.

 

[Les]

One term to look at as well is color temperature. HID lamps are much higher in the spectrum (bluer). This makes it really hard to do an apples-apples comparison to something like a Source Four since an HID's punchy, crisp white output will appear brighter than an incandescent counterpart even though it may not necessarily be putting out more lumens - although they usually are.

A good example of this would be stadium and gymnasium lights, which use the same basic technology. A common gym light uses a 400w Metal Halide lamp.
Notice where tungsten halogen falls on the scale below. HID lamps start somewhere in the area of noon sunlight and above (The MSD575 lamp specs at 6000 Kelvin).



This also comes in to play when you add Metal Halide fixtures to conventional systems. Getting them to match (if that's what you want) can be tricky as they stick out like a sore thumb.

 

[TJCornish]

The other factor not mentioned is what you put between the lamp and the front lens element. I use 700w discharge-based movers. At full open, they are about 14,000 OTF lumens. My particular fixtures have CMY color mixing, a color wheel, two gobo wheels and a prism. Putting any combination of all of that stuff in the optical path GREATLY reduces the output, so if you are shopping for profile movers, keep that in mind, too.

I generally tend to use mine for gobo projection and typically keep them at open white. In this usage, they are plenty bright on a 575w-level stage. Like any other fixture, saturated gels whack the output VERY significantly. I believe the Congo Blue color wheel color has something like a 4% transmission ratio.

BTW, I rented some Martin Mac Quantum Profiles, which are LED-based. I would consider them roughly the equal to my 700w discharge fixtures.

 

[JD]

The final factor in discharge lamps vs LED has to do with what happens to the output when you get into saturated colors. This has to do with how the colors are mixed.
Metal Halide = Subtractive mixing.
LED = Additive mixing.
Basically, in subtractive mixing, you start with white light and subtract out all the color you don't want to get the color you do want. In additive mixing, (LED) you start with primary colors and then add them together to get the color you want. What this means is that if two fixtures were rated at the same output when white, the LED fixture would produce a lot more usable light when you were trying to achieve a deep color like blue. Not all LED fixtures are additive, but in most cases an LED fixture where you control the color via DMX works by controlling various LED output values, as compared to using a filter system.

 

[JChenault]

The final factor in discharge lamps vs LED has to do with what happens to the output when you get into saturated colors. This has to do with how the colors are mixed.
Metal Halide = Subtractive mixing.
LED = Additive mixing.
Basically, in subtractive mixing, you start with white light and subtract out all the color you don't want to get the color you do want. In additive mixing, (LED) you start with primary colors and then add them together to get the color you want. What this means is that if two fixtures were rated at the same output when white, the LED fixture would produce a lot more usable light when you were trying to achieve a deep color like blue. Not all LED fixtures are additive, but in most cases an LED fixture where you control the color via DMX works by controlling various LED output values, as compared to using a filter system.

Not necessarily. There are a number of white LED fixtures. These use color wheels, etc and do subtractive mixing. I.E. Just because it is an LED fixture does not necessarily imply multi color LEDs

 

[TJCornish]

Not necessarily. There are a number of white LED fixtures. These use color wheels, etc and do subtractive mixing. I.E. Just because it is an LED fixture does not necessarily imply multi color LEDs

Indeed. Wash movers tend to be additive, but profiles tend to be white LED sources with CMY mixing or color wheels. I suspect there are a couple reasons for this: First, most of the LED R&D is directed at white emitters so they are ahead of the colored emitters, and second, it takes many more emitters to do the colored source, as you need to have R,G,B, W/A, etc. This makes the optical design more complicated as it has to focus the larger light source.

I expect we'll get there, and when we do, it will greatly reduce the number of moving parts, and therefore hopefully the cost goes down and the reliability goes up.

 

[StageTech620]

So generally speaking. Overall, would a 280W Metal Halide moving head, with a color wheel, be better for stage use, or a 150W LED moving head, with RGB color mixing.

Thoughts?
Positives and Negatives to each?

 

[Thetechmanmac]

In terms of brightness, a Metal Halide is ALWAYS going to be brighter than an LED. This thread talks a little more about the details of HMI lamps.

As for which one, it depends on what you really need. Do you want brightness and punch, or do you want to be able to "create" your own perfect color? Some color wheel parts can be interchangeable so. Color mixing really allows you to get to that specific color you're looking for without being constrained by the color choices of the manufacturer.

Which models of movers were you looking at in particular?

 

[Les]

I can only offer physical evidence since you'd really need to have each in your space to get a definitive answer on intensity or punch. Factors such as throw distances, footcandles from other fixtures, etc really come in to play more than the type of technology employed. The actual moving heads you're looking at matter as well. I've seen optically efficient 250w moving heads out-perform a cheaper 575w HID moving head, for example.

As far as advantages/disadvantage

HID Pros:
• Established - Proven technology in wide use for many years
• Intensity - Generally very bright*
• Price - Sometimes cheaper initial cost

*Some LED fixtures can easily outperform 250w MH fixtures these days. 700w and up seems to be where MH still dominates.

HID Cons:
• Weight - HID fixtures generally have very heavy ballasts and associated components within
• Maintenance - Power factor capacitors and ignitors do wear out from time-to-time
• Warm-up/Re-start - HID fixtures need a warm-up period of about 5 minutes, and most need to cool for at least 10 minutes before being re-started. It is generally a good idea to leave fixtures lamped-on unless you're done using them for the day. No on/off, on/off. It kills the lamps
• Sensitivity - Slight power fluctuations can cause the lamp to extinguish, making you wait for ten minutes before lamping back on. Had this happen in a show (during a storm) once. Can confirm, does suck
• Light Leak - Since HID fixtures will be lamped-on during the show, you will get a little light leak from cooling vents of the fixtures. Not enough to affect what's on stage, but enough to draw attention when the fixtures can be seen by the audience, especially during a blackout
• Heat - HID/Arc lamps still produce considerable heat, which is hard on components
• Lamp cost - Budget about $200 per lamp. HID lamps also "color shift" as they age, which can be annoying
• Current draw - 250w units aren't too bad, but it can get tricky when more/higher wattage units are added

LED Pros:
• The exact opposite of HID "cons". LED fixtures are lighter, need no warm-up time, don't use expensive lamps, and the light source can be switched on/off rather than doused.
• Color mixing - *some* LED fixtures have RGBA/W LEDs for color mixing; eliminating some moving parts

LED Cons:
• Upfront cost on higher-end fixtures is generally greater
• Not exactly "time-tested" - These fixtures will last ten years in theory, but they are very much still in their infancy
• Obsolescence - Something way better will be out next year. MH fixtures were like this for many years but eventually leveled out. Your LED fixtures will still be good fixtures, but you may experience buyer's remorse once the "LED MOVER 2.0" comes out, which blows yours away for the same price and half the weight. It's a developing technology and will be for a while

Suggestion: If you're looking for some good mid-level LED movers, check out the Chauvet Rogue line. I have heard very good things about them.

 

[DELO72]

So generally speaking. Overall, would a 280W Metal Halide moving head, with a color wheel, be better for stage use, or a 150W LED moving head, with RGB color mixing.

Thoughts?
Positives and Negatives to each?

No. It depends on what it does, and a lot of other factors. Is it a Beam, or a spot? or a wash? How do you intend to use it? Do will it be as a key light on the performers? If so, you need to think about the CRI of the light source and fixture or your actors are going to look pale and sickly. A 280W BEAM fixture (I would argue) is not a good option for a stage (theatre/dance). a 1000W HID fixture with a high CRI and quiet fans (that is a performance or spot) IS a good option for most use. You need to first consider "what do we want to use this for", and then break out what each fixture is capable of and find the fixture(s) that meet the use criteria best. It isn't all about intensity.

 

[DELO72]

HID Cons:

• Heat - HID/Arc lamps still produce considerable heat, which is hard on components
• Lamp cost - Budget about $200 per lamp. HID lamps also "color shift" as they age, which can be annoying
good things about them.

One thing to note- LEDs ALSO color shift as they age because the heat causes the phosphor to degrade over time. Especially in the reds. Some fixtures have sensors and feedback software built in so they adjust for this decline and color shift, but that means "dimming down the other colors to try to compensate".

LEDS also produce considerable heat, which is similarly hard on components. Their heat is mostly out the back, and the components affected tend to be the circuitry and ECG, not the forward items such as the color/gobo wheels, shutters, etc.

There is no such thing as a perfect light source. Each has its pros and cons.

 

[JD]

One thing to note- LEDs ALSO color shift as they age because the heat causes the phosphor to degrade over time. Especially in the reds.

Should note, this has to do with "white" LED elements, which basically use a deep blue source that reacts with the phosphor to produce white light. As the phosphor ages, they shift away from red and toward blue. Some other LEDs (outside or RGB) also use phosphor to achieve color. The actual Red, Green, and Blue LED's are monochromatic, producing tight bandwidths from the diode itself and do not use a phosphor. These do not color shift with age. Which brings me to age. LEDs DO age! They tend to have a higher than rated output when new, but as they age, micro-cracks form in the junction and slowly decrease their output. How fast? Well, it's hard to tell. Very few "full life" tests have been done on 50,000 hour LED emitters, because they would take... well... 50,000 hours! Instead, predictions are made based on the expected degeneration. Another thing is the "failure point." In some cases, the LED will stop cold. This happens when the tie-wire that connects the junction to the input leads breaks. In other cases, life is based on the point at which the junction fails to emit a % of the rated output. So, how do they come up with the lifespan numbers? You tell me! I am not sure there are clearly established industry ratings yet, so the same LED that is rated by one source may be 20,000 hours, and another 50,000 hours. As always, the more reputable a product manufacturer is, the better chance their numbers are conservative. To date, I have only seen the catastrophic type failures, where the diode goes open-circuit or shorts.