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What is Pulse Start Metal Halide (PSMH) and How Do I Build a Ballast ?

Written by: The Professor (Sept. 15, 2003)


Safety Exercise proper safety precautions when working with any electrical devices. The author of this document is not liable for your mistakes. This page is provided for information purposes only. The reader assumes all liability for use or misuse of any information contained herein.

This FAQ will, very briefly, explain indoor lighting in general, and PSMH lighting in particular.

This FAQ describes how to build a PSMH ballast. Compared to building a High Pressure Sodium lighting ballast it is
as difficult or as easy, it is as dangerous or as safe. If you are familiar with ballasts and electrical components then there
should be no problems. Otherwise you can e-mail this page to a friend or to your local hydroponic store. Let them do it.


There are two types of High Intensity Discharge (HID) lights commonly used, (with success), for indoor growing. These are High Pressure Sodium (HPS) and Metal Halide (MH).

Included in the category of HID lighting, but not part of this FAQ, are self-ballasted Mercury vapour lamps which simply screw into a regular socket - they are cheap (in the short run) and inefficient (expensive in the long term). Low Pressure Sodium, (not HPS), lighting - it is monochromatic and of the wrong spectrum for growing plants. Xenon strobes, HMI (short-arc MH), UV lamps, Sulphur bulbs and other electrodeless lighting are all not further discussed in this FAQ. Fluorescent lights are not HID lights and thus are not part of this FAQ either. Icetron electrodeless fluorescent lights are too expensive, dim and not HID - so are not included either.

This FAQ is intended for both smart beginners and experts. If you are new to indoor growing using artificial light you are likely best off to simply buy a 600W HPS light from a reputable hydroponic store. Ask about the warranty.

You will save very little buying a 400W HPS system and may find yourself without enough light, unless you also buy a light rail to move the light. In that case you are probably better off buying either two 400W or 600W lights. If you know (somehow) you will only buy one light and can afford a track you might consider a 1000W HPS system, without a light rail you will likely have too much light in the center and not enough at the edges of your grow. It all depends on your setup - find another FAQ for more info.

The purpose of this FAQ is to assist you to decide if you should purchase a PSMH light and provide a little assistance in choosing which size to purchase. Detailed information on using the light efficiently (either growing "in-the-round" or using a light rail) and using a timer are not within the scope of this FAQ. Further detailed information on lighting is available already in other OverGrow FAQs.

Note: To read less information skip the BLUE tables.

Some wisdom from various places on the Net about PSMH:

Pulse-Start Metal Halide Bulbs

Lamp manufacturers sought to improve traditional probe-start metal halide lighting (>150W) by changing the chemistry and increasing the fill pressure in the lamp arc tube to increase lumen efficacy (lumens per watt). However, probe-start lamps, with only a 600v peak starting voltage from the ballast, would not start where these improvements had been made. Furthermore, removal of the starting probe and associate bimetallic switch from the arc tube construction allows for optimized arc tube design and manufacturing process making the chemistry/fill pressure changes possible. Advance introduced an ignitor as a component of the ballast to deliver a high voltage pulse directly across the lamp's operating electrodes to start the lamp - similar technology as that used for high pressure sodium and low wattage metal halide. The ignitor replaced the ballasts' 600v peak voltage and eliminated the lamp's internal starting probe and its protective switch.

As described in the next section on pulse-start ballasts for metal halide lamps, this technology improves the overall performance of metal halide. Lumen output per watt consumed increases by 25% to 50%, depending on lamp wattage and burning cycle, and lumen maintenance is improved as much as 15-25%. In addition, lamp life is extended, color rendition is improved, and warm-up time is cut to 2 minutes.

Pulse-Start Metal Halide Ballasts

Pulse-start metal halide ballasts specifically meet the needs of pulse-start lamps and are not simply probe-start ballasts with added ignitors. Replacing the internal lamp starting probe with an ignitor allows a separation of ballast starting and operating functions. The ignitor starts the lamp and the ballasts' core and coil operates the lamp, allowing for optimization of both lamp and ballast performance.

The traditional CWA metal halide ballast, with its 600v peak open circuit voltage needed to start probe-start metal halide lamps, creates a relatively high lamp current crest factor that compromises lamp performance. Focusing the ballast design solely on lamp operation lowers the lamp current crest factor - resulting in improved lamp life, lumen maintenance and color stability. Isolating lamp starting and operating functions also result in more efficient and cooler ballast operation, as the core and coil no longer needs to supply the 600v starting voltage. This lower open circuit voltage creates lower ballast operating temperatures, resulting in longer ballast life, reduced maintenance/replacement costs, and the possibility of higher fixture ambient temperature ratings.

Optimized pulse-start ballast/lamp systems boost maintained lumen output by 25% to 50%. Improving the quality and quantity of white light throughout lamp life provides energy savings, since lower wattage pulse-start lamps produce the same light output as higher wattage probe-start lamps. By achieving lumen maintenance of up to 80%, pulse-start lamps reduce light loss over the life by up to one-third compared to probe-start metal halide. Fewer watts per square foot are required because consistently higher light levels are assured throughout lamp life. Other improvements of pulse-start ballast/lamp systems over traditional probe-start systems are in color rendition, lamp-to-lamp color consistency, and reduced color shift.

Advance offers ballasts in Super Constant Wattage Autotransformer (SCWA), Linear Reactor and Regulated Lag circuits. SCWA ballasts, the pulse-start version of CWA ballasts are available in 150W to 1,000W. Linear Reactor ballasts, for 277v applications, are available in 150W to 450W. Regulated Lag ballasts are offered in 175W to 450W for applications with long burning hours and/or heavy industrial applications with large power fluctuations.

From the Venture Tech Center FAQ:

Q. Is it possible to add an ignitor to a standard CWA ballast to convert the system to pulse start?

A. Not really. Many of the present metal halide ballasts in the marketplace have poor sustaining voltage performance. If you add an ignitor, it does nothing to improve sustaining voltage. All of the pulse start ballasts Venture has designed have approximately 270 volts sustaining which is about 50 volts higher than standard metal halide In all likelihood, the many lamps available would probably start and operate properly for a while, but who knows how long. Venture's pulse start ballast have a better current crest factor and lower current off-time, which is much better for the lamp.

From Acuity Lighting (Lithonia) Features & Specifications:

SCWA Ballast Electrical System:

The SCWA is comprised of a two-coil ballast, ignitor, and capacitor for lamp stabilization.

Ballast - Available in 120V, 208V, 240V, 277V and 480V. In Canada, available in 120V, 277V, and 347V. For other voltages, consult factory. A +/-10% line voltage fluctuation results in a lamp wattage regulation of +/-10%. Operates lamp at a crest factor of 1.60. Unlike probe start CWA ballasts which rely on a high crest factor to start the lamp (typically 1.80), the SCWA system uses a pulse ignitor. Because the lamp current is closer to a true sine wave, less stress is placed on the arc tube electrodes, resulting in smoother lamp operation. Consistent color over lamp life. The SCWA ballast circuit operates the lamp more gently than a standard CWA circuit.

Lamp - Hot restrike times of less than 7-10 minutes. Because the starting of the lamp is accomplished through a pulse ignitor, the normal cool-down period before re-ignition has been substantially reduced.

According to Philips:

Q. Why choose Pulse Start metal halide lamps over standard switch start quartz metal halide lamps?

A. Pulse Start metal halide lamps offer an improved performance over standard switch quartz metal halide lamps. Pulse Start offers increased efficacy (up to 110 LPW), improved lumen maintenance (10-15% increase), longer lamp life (15,000-20,000+ hours), faster run-up time (2 minutes vs. 4 minutes), quicker re-strike (4 minutes vs. 15 minutes) and colder ignition temperatures (-40'F vs. -20'F) than standard switch start quartz. Pulse Start offers a total cost of ownership solution with reduced maintenance costs and energy savings.

Reasons NOT to buy PSMH:

1) Availability - you probably will get strange looks at the hydroponic store.
2) Cost - expect to pay 10% LESS if you are very lucky, 50% more if your not.
3) Support - Don't expect any help (except perhaps from this FAQ).
4) D.I.Y. - you'll be building everything yourself.
5) Relatively new technology - for some this is another thing to worry about.
6) Fewer choices of bulb colour (most are 3900 Kelvin).
7) Fewer choices of bulbs (and operating position is usually vertical).
8) It is Metal Halide - you may be one who prefers to use only HPS.
9) Your a technophobe, a Luddite, you just can't do it.

Reasons to buy PSMH:

1) The above reasons to NOT buy will change soon - when more people buy.
2) If you know how to build a HPS ballast then you know how to build a PSMH one.
3) You get your money back in less than two years, likely 6 months.
4) Relatively new technology - for some this is another thing to rejoice about.
5) Lower energy consumption - more lumens per watt (L.P.W.) - up to 25% to 50% more.
6) More choices of wattage - choose exactly the size you think you need.
7) Faster cold and hot starts - provides instant light and reduces wear.
8) Longer bulb life - lumen maintenance of up to 80%, use bulbs twice as long.
9) Colder temperature starting - not that this would matter much to most people.
10) Better colour (Kelvin) stability - not that this would matter much to most people.
11) Lamps are more consistent in colour - not that this would matter much to most people.
12) Lower ballast temperature, smaller physical size - important for some people
13) The best, newest MH bulbs will be PSMH - Ceramic PSMH is better than a retro-bulb.
14) It is Metal Halide - better for vegetative stage - (MIGHT be HPS compatible).
15) Each time you re-start your light it gets 'dirty' - PSMH stays cleaner.
16) It is the way of the future - why buy outdated technology and stay in the dark :) .


Getting Started:

You might wish to read these OverGrow FAQs:

Building and buying an HPS system - Ballast information
How can I build my own HPS or MH light system? - Ballast information
GrowFAQ Electrical Safety Hazard Warning, The Physical Effects of Electricity - Lighting  

The PSMH bulbs and ballasts are available in a large variety of sizes. I suggest a 400 watt system. You can skip to the parts list to get the info to build such a system or you can read the details to follow to specify exactly the size you want, all help is provided for a couple of manufacturers.

Bulbs/Ballasts are available in these (and other) sizes: 320, 350, 400, 450, 750, 1000 watts. Please note that there are new facts to know about PSMH systems - a 360 watt bulb is designed to work in a 400 watt ballast (almost as much light, but you save 40 watts of electricity). A 750 watt bulb will product almost as much light as a 1000 watt (old fashioned) metal halide bulb. A 1000 watt PSMH bulb will really be powerful and need to be tracked so as not to cook your plants (unless you are growing "in-the-round"). Two of those bulbs in an Omega Garden will really turn heads.

Throughout this FAQ "Advance" and "Philips" are suggested manufacturers. The best ballasts are supposedly available from Delta. I also like the looks of Lithonia/Acuity and Holophane but have not tested them. You can search the Internet for more info and build your own the way you wish or use the suggested parts and build one similar to mine, your choice.

So skip to the parts list or read on ...  

Choose your preferred ballast type: ( I suggest SCWA ).

Pulse Start Compatible Ballast Transformer Types:

LLRPSL - Linear Reactor Pulse Start ballast - 277 volt only - 450W max. - Poor Dip Tolerance.
SCWA - Super Constant Wattage Autotransformer - I recommend this type.
SCWI - Super Constant Wattage Isolated Autotransformer - Best? - have not tried.
RLB - Regulated Lag Ballast - Excellent Dip Tolerance - Largest Start Current.
CWA - NO NO NO! - Don't use a CWA ballast - Find an intelligent salesperson !

Extra Ballast Specification Info - Customize your own system:

Refer to Lithonia Lighting's Pulse Start Specification Guide for more info:

HID Ballasts Pocket Guide/Troubleshooting - I didn't need this!

Ballast Specification Factors

Ballast Handbook - EXCELLENT

Super CWA for Pulse-Start Metal Halide Lamps (69KB) HI-4000-R01

HID Ballasts for Pulse-Start Metal Halide Lamps (1.5MB) HI-4020-R01

Linear Reactor for Pulse-Start Metal Halide Lamps (103KB) HI-4040-R01

Reg Lag for Pulse-Start Metal Halide Lamps (121KB)

Trends in Metal Halide Technology:

Advance Catalog - Section 4, High Intensity Discharge Ballasts (5.0MB):

Xtenza Data Sheet (55KB) HI-4010-R02:

Dry Metalized Capacitor (56KB) 1703:  

Need an already built ballast that takes multiple wattages, uses least power, runs bulbs gently and longer than ever (but is not the best for CMH bulbs):

Pulse Start Digital Ballast - $320 - Just plug it in and go. Has dimming too.
DynaVision 320/350/400W for Pulse-Start Metal Halide Lamps (1.5MB) EH-5010-R01  

Choose your bulb:

Currently only Venture ( offers a proper horizontal operating position bulb and it must be used in an enclosed fixture due to risk of explosion. You could use any PSMH bulb in the horizontal position in an enclosed reflector but don't expect all the benefits of PSMH to apply - it won't last long, unless it's a specific Venture bulb. Other manufacturers do make bulbs that are smaller than 400W and work HOR. 400W PSMH bulbs are the size I suggest - you might want a 750W but bulb choices are currently very rare. 400W ballast does largest variety of bulbs.

Many, but not all, bulbs are available for open fixtures in the vertical operating position. If you are using a bulb in the vertical position with a parabolic reflector then it must be open rated! I've yet to see a parabolic reflector with a glass/acrylic covering, (the reflectors are too wide and shallow) from a hydroponic store. You can buy a proper medium/low-bay fixture for big bucks from a lighting distributor - it may be very (too) heavy also.

Check Iwasaki's catalog for a 400W PSMH reflector bulb that is open rated. This will let you hang a mogul/octagon-socket from a chain with no reflector.

Philips Lighting - TDS - MH005 - Pulse Start Metal Halide 400 Watt Lamp (Clear) 3900K

Philips Lighting - TDS - MH006 - Pulse Start Metal Halide 400 Watt Lamp (Coated) 3700K  

Parts List:

Suggested Parts to Order (when calling a lighting distributor):

If in the British Columbia (Canada) area I offer these tips. If there is the word "brite" in the company name, they are not. If they have fluorescent in their name, don't bother. Remember whoever you do call is busy selling 100+ systems to someone who knows what they are doing - that is not you. Don't bug them! Foil Head

If you want to spend less than $220 (Canadian) then get a 400W system. DON'T ask the lighting distributor for parabolic (grow-op) reflectors UNLESS they specifically advertise that they sell hydroponic lighting - they'll hang-up.

Remember a 1000W PSMH system is very powerful and MUST be tracked! The other sizes are currently less popular (but likely will be more common in future, or they will be like beta cassettes.) A 750W PSMH is nearly as strong as a 1000W probe-start (regular) MH system - but saves 250 watts. 360 watt PSMH bulbs are designed to work with 400 watt PSMH ballasts so this gives you greater bulb choice. They are not quite as bright (and cost more) but you save 40 watts of electricity. A 400 watt PSMH bulb would be equivalent to a 600 watt probe-start MH bulb (if there were such a thing) since the lumen maintenance level is much better with PSMH.

Suggested 400W Pulse Start Metal Halide System:

1) Advance 71A6092 Super CWA Ballast (or 71A60A2) - comes with Cap. + Regular Ignitor
2) Advance L1533-HR Xtenza Ignitor (they should swap ignitors for FREE)
3) Philips MS400/BU/PS Pulse Start Metal Halide 400 Watt Lamp (Clear)
4) 600v 5KV standard (NOT open) mogul socket
5) 3 wire, 14 gauge black cord (get two 20 ft. ones, or longer?)
6) Grotek Ballast Box with Louvers (from hydroponic store)

If you already have a lighting system (adding a 5KV mogul is recommended) you only need to buy four parts and swap the old ones out. It is probably best to keep the old one and build another new one. Don't be cheap.

To request a quote from a lighting distributor for the above parts simply say:
"I would like a price quote on an Advance Ballast 71A6092 (or 71A60A2) with an L1533-HR Xtenza Ignitor, a 600v 5KV standard (NOT open) mogul socket and a Philips MS400/BU/PS Pulse Start Metal Halide 400 Watt Lamp (Clear)."

The above should be well under $200 (Canadian). The wire is available cheaply from a hardware store. Don't bother trying to get the box from them (unless they specifically sell "hydroponic lighting" - in which case they will probably be more expensive and you may as well call elsewhere). It's just that easy.


Pulse Start Metal Halide Parts Pictures

A SCWA ballast with a standard ignitor and a metal-can capacitor.

The suggested Philips MS400/BU/PS Bulb.

The MasterColor Pulse Start Ceramic Metal Halide Bulb (notice the spectrum of the 4K version). Build this ballast to run this bulb if for no other reason. It has a molecular spectrum - no more spikes!

A 5kv Mogul - DON'T get a pink one, it won't accept HORizontal bulbs in the future. MAKE SURE your bulb base is NOT an EX type unless you have an enclosed reflector.

TWO - 14/3 Power Cords, one a convenient length (for the wall socket) the other, up to 50 feet long (if using an Xtenza ignitor). Always allow extra length for both.

I suggest an aluminum ballast box with louvers.

Mount your mogul on an octagon box (with lid) for safety.

This is what enclosed reflector bulbs look like (The Philips MS400/BU/PS model looks like this also though it is open rated). Parabolic reflectors are NOT enclosed reflectors (usually). Horizontal reflector may (or may not be enclosed) but most PSMH bulbs do not operate in the horizontal position. This will change soon. :(

This is what a protected PSMH bulb looks like - slightly less lumens - much safer! Notice the wire coil.  

If you need something other than 400W simply order different parts using the catalog URLs provided above. This FAQ provides all the information you need but does NOT provide training in electronics. Make certain the bulb is open-rated if your reflector is not enclosed. Know what your doing, don't do what you don't know.

Ballast Building Tips:

* I recommend using an Advance ballast and an Xtenza Ignitor (0-50 ft. strike range).
* If using an Xtenza use 5 ft. more wire than you think you'll need (up to 50 ft.)
* The PSMH circuit is the same as the HPS circuit (look on the ballast for schematic).
* Mount the ballast transformer an inch away from the side walls of the box.
* If using a Plastic Dry Film Capacitor mount it sideways towards the front of the box.
* If using a Dry Film Cap. and Xtenza Ignitor the cap. looks like an ignitor and vice-versa.
* Add an "all-in-one" switch, fuse and pilot light to the front of ballast.
* Add feet to your ballast to avoid burning the floor, keep water out and further improve cooling.
* Use 1 inch post bolts with cup washers for case feet - alternately use regular bolts and two nuts each.
* Make the lamp wire pluggable - Use a peculiar plug for the lamp wire to avoid trouble.
* Use an aluminum box and leave the protective plastic ON (until you plug it in) to avoid scratching.
* Cover the unused transformer input leads with electrical tape but use Marrettes elsewhere.
* Follow proper safety procedures - know them before you do this.
* READ GrowFAQ Electrical Safety Hazard Warning, The Physical Effects of Electricity - Lighting
* Use a conduit bracket for dry film capacitor (and regular ignitor if you decide to use a regular ignitor).
* Use bakelite or small cork "table savers" to insulate handle and attach handle with bolts NOT sheet metal screws.
* Always use ALL ground wires - ground mogul's octagon box (and reflector) - ground case.
* IF you cut the ballast bolts put the nuts on before cutting - cut them too long. Use split washers. Transformers vibrate.

* Warning: Self-tapping sheet metal screws will cause grindings in the case - assemble empty case, unscrew carefully, clean it. Be careful when later re-inserting self-tapping sheet metal screws to avoid stripping threads - reverse turn them to find thread. You don't want metal shavings in your ballast.

Don't expect that the home-made-hydro-store ballast was made this carefully - check it - it's your grow, your fire. It takes years of accumulated knowledge to know all this stuff. Read this FAQ carefully OR get someone who understands it.  

Internal Parts Layout:

This layout is for a 400W SCWA PSMH ballast. You may have to turn the Xtenza (Ignitor) 90 degrees and stack it above the capacitor for larger wattage systems. Keep the ballast one inch from walls (if possible) and away from the plastic capacitor. Large ballasts use oil-filled capacitors but keep it away from the transformer, to avoid overheating, in any event. The bottom of the box near the front should be the coolest location. Place ballast outside grow area to avoid heat / water and allow easier usage.  

400W SCWA PSMH Ballast 
Click HERE for huge picture
Click HERE for small picture

Caution for ALL Metal Halide Bulbs:

Turn your Metal Halide light OFF at least once per week (some manufacturers recommend 1 hour (Iwasaki), others suggest only 15 minutes (Philips) is needed). This is necessary for the bulb's getter to re-establish itself, otherwise you may get a non-passive failure (explosion). This applies to PSMH and probe-start (regular) MH. This does not apply to pulse-start or retro-HPS Ceramic Metal Halide (CMH). Use a timer, not your memory. This only is needed for 24 ON usage, if your doing 12/12 don't worry about it.


If you have questions please post them in this thread. The OverGrow moderators of the FAQ will compile your comments and fix this up for us should the need arise. Foil

REMEMBER: Wire it correctly, put the cover on, cross your fingers, fire it up! IF you must disassemble it discharge the capacitor with a large resistor (use a toaster if you must) don't use a screwdriver! Don't kill yourself.

It is really simple but you can pay the hydroponic store $30-50 to wire it for you. Once you've plugged it in you'll need to wear rubber gloves if you open it. Always Be Careful.

Good Luck,
The Prof.

PS: In a few months I'm going to sneak over to the op and watch them put a HPS bulb into the PSMH system. It is my understanding that the open-circuit voltage will be much too high and the operating voltage will be a little too low. Still it is expected that it will work - but the engineers give no warranty. I'll keep you informed. The OCV should not matter, the OV will result in a lower (HPS comparative) efficiency - still better than MH though.

Last modified: 04:20 - Oct 02, 2003