Key takeaways
- Ten 315W CMH lamps, one test rig, one variable. The number that matters is the sum of every PAR reading across a 5′ × 5′ footprint.
- Philips MasterColor 3100K took the test at 10,678, about 7% clear of the next lamp. We no longer carry it, and this article says so rather than pretending otherwise.
- The highest-scoring lamp still in our catalogue is the SunPulse 3200K at 9,971, followed by Growers Choice 3100K at 9,676.
- On relative UV between 250 and 400 nm, the Ushio 3000K led at 8.6 against a low of 6.0. That spread is wider than we described it at the time.
- 3000K reads warm and HPS-like with energy near 600 nm; 4200K spreads broader and whiter with its peak closer to 500 nm.
Hey everyone, Nate with GrowersHouse here. We tracked down every 315W ceramic metal halide lamp we could get hold of, ten in total, and ran them all through one test rig so the only thing changing was the bulb itself.
This version of the write-up publishes the actual numbers. The original told you which lamp won and by roughly how much; below you will find the full PAR totals and UV readings for all ten, so you can weigh them against what matters in your own room rather than taking our word for the ranking.
What CMH Is, and What It Is Not
First thing worth clearing up: a ceramic metal halide lamp is not just another metal halide. People hear "metal halide" and assume veg-only. That is not what this technology is.
A traditional metal halide runs a fused quartz arc tube. A CMH lamp runs a sintered alumina ceramic one, and that ceramic holds together above 1200 kelvin. Quartz has a problem at those temperatures: metal ions migrate into the silica, which shifts the colour and costs output as the lamp ages. Alumina does not do that.
The published consequences are a luminous efficacy of roughly 80 to 117 lumens per watt, 10 to 20% better than quartz metal halide, a colour rendering index between 80 and 96, and a rated life up to 24,000 hours. High CRI is why these lamps look like daylight rather than the orange wash of HPS.
For a grower the more useful framing is simpler: how many usable photons land on the canopy per watt going in. That is what we set out to measure.
Sockets and fixtures
315W CMH lamps are physically small and do not use the mogul base most HID gear expects. You need a purpose-built 315W CMH fixture or a compatible adapter. One exception in our range is the GrowLite 315W single-ended mogul base lamp, which is built for the socket you probably already have.
How We Ran the Test
One variable only. Same ballast, same mounting height, same fixture, same measurement routine for every lamp. Whatever differences turned up had to come from the bulb.
- Ten lamps. Five in the 3000K to 3200K class, five in the 4000K to 4200K class.
- Five footprint sizes. Readings taken across 1′×1′, 2′×2′, 3′×3′, 4′×4′ and 5′×5′, then summed.
- Relative UV. Intensity between 250 and 400 nm, measured at 24 inches. This is a comparison within the 315W CMH class, not an absolute UV measurement.
- Spectral captures for each lamp, grouped by colour temperature.
One honest limit on the method. A proper photometric lab measures thousands of points with instrumentation we do not have. We took a few dozen per lamp. That is why the summed totals across the larger footprints are the figures we lean on, and why a single hot-spot reading is the one number you should ignore.
PAR Results: All Ten Lamps
Here is what the original version of this article never published. The sum of every PAR point across the 5′ × 5′ footprint is the headline figure, because it uses the largest sample and reflects real coverage instead of rewarding a bright centre.
| Rank | Lamp | Colour temp | 5′×5′ PAR total | Against the winner | Still carried? |
|---|---|---|---|---|---|
| 1 | Philips MasterColor CDM-T Elite Agro | 3100K | 10,678 | — | No |
| 2 | SunPulse | 3200K | 9,971 | −6.6% | Yes |
| 3 | Nanolux MaxPar | 3100K | 9,708 | −9.1% | No |
| 4 | Philips CDM Elite | 4200K | 9,694 | −9.2% | No |
| 5 | Growers Choice | 3100K | 9,676 | −9.4% | Yes |
| 6 | Solis Tek | 3200K | 9,519 | −10.9% | As a fixture |
| 7 | Ushio HiLux Gro | 3000K | 9,472 | −11.3% | Yes |
| 8 | Nanolux MaxPar | 4200K | 9,426 | −11.7% | No |
| 9 | Ushio HiLux Gro | 4200K | 9,378 | −12.2% | Yes |
| 10 | Growers Choice | 4200K | 9,218 | −13.7% | Yes |
Two things stand out once the numbers are on the page. The first is that the gap from first to last is under 16%. Every lamp here is in the same broad performance band, which means colour temperature, availability and the fixture you are running matter at least as much as picking the top of the table.
The second is that the top of the 3000K class beats the top of the 4200K class, and the pattern holds all the way down. Warmer lamps in this test simply put out more measurable PAR.
A correction to the original write-up
The earlier version of this page said the Philips 4200K came in "just under 5% ahead" of the Nanolux MaxPar 4200K. Against the 5′×5′ totals the real figure is 2.8%, and no footprint size in our data produces 5%. The Philips 3100K lead over SunPulse was given as roughly 8%; it is 7.1%. The rankings were right, the margins were overstated, and the table above is the record.
3000K Against 4200K
The colour temperature question is the one growers ask most, and the spectral captures answer it better than any marketing sheet.
In the roughly 3000K group, intensity concentrates near 600 nm. That is the warm part of the spectrum and it is why these lamps look orange-yellow, much like HPS. There is a notable spike just north of 800 nm and then output falls away, with little past 900 nm.
The 4200K group spreads its energy more broadly with the peak nearer 500 nm. Charts alone will mislead you here: side by side, the 3K lamps feel more intense while the 4K lamps cover more ground spectrally. Both readings are correct, and they are measuring different things.
A practical note the charts do not show. The high CRI is what makes these lamps genuinely pleasant to work under, and it is why problems get spotted earlier. The Ushio 4200K is rated above CRI 95, the 3000K version above 90. If you scout your own plants, that is worth something no PAR total captures.
UV Results
Our UV figures are relative, measured between 250 and 400 nm at 24 inches. That band is mostly UVA with some UVB. Treat these as a ranking inside the 315W CMH class rather than an absolute dose.
| Lamp | Colour temp | Relative UV | Still carried? |
|---|---|---|---|
| Ushio HiLux Gro | 3000K | 8.6 | Yes |
| Nanolux MaxPar | 4200K | 8.2 | No |
| SunPulse | 3200K | 8.2 | Yes |
| Solis Tek | 3200K | 8.1 | As a fixture |
| Philips MasterColor | 3100K | 7.8 | No |
| Philips CDM Elite | 4200K | 7.7 | No |
| Nanolux MaxPar | 3100K | 7.5 | No |
| Ushio HiLux Gro | 4200K | 6.5 | Yes |
| Growers Choice | 4200K | 6.1 | Yes |
| Growers Choice | 3100K | 6.0 | Yes |
Two corrections to what we said the first time. We described the spread as not massive; from 6.0 to 8.6 is a 43% difference between the highest and lowest lamp, which is substantial if UV is what you came for. And we named the MaxPar 4200K as runner-up without mentioning that the SunPulse 3200K tied it at 8.2.
The caveat still stands, though. These are low numbers next to the PAR figures. A 315W CMH lamp gives you some UV as a side effect of how it makes light; it is not a UV solution, and if UV is the goal you want dedicated fixtures.
Which Tested Lamps We Still Carry
This test ran in 2016 and the catalogue has moved since. Rather than quietly editing the winner out, here is the plain position on all ten.
- Philips MasterColor 3100K, the test winner, is no longer in our range. Neither is the Philips CDM Elite 4200K. We have not stocked Philips CMH lamps for some time and there is no equivalent listing to send you to.
- Nanolux MaxPar, both colour temperatures, is also gone.
- The Solis Tek 3200K lamp we tested is no longer sold on its own. Solis Tek is still represented by the Solis Tek C1 complete fixture, though that ships with a 3100K lamp rather than the 3200K one that placed sixth here.
- Five of the ten are still on the shelf: SunPulse 3200K, Growers Choice 3100K and 4200K, and Ushio HiLux Gro in both 3000K and 4200K.
Which makes the practical reading of the table straightforward. The best-performing lamp you can actually get from us is the SunPulse 3200K at 9,971, about 6.6% behind the Philips that won. If UV matters more to you than raw PAR, the Ushio 3000K topped that measurement outright.
Worth adding: the two Growers Choice lamps publish manufacturer PPF figures the others do not. The 3100K is rated 565 µmol/s and the 4200K 535 µmol/s. Those are the manufacturer's numbers measured their way, not ours, so do not read them against our relative PAR totals.
Fixtures and Ballasts
A 315W lamp needs a matched fixture and ballast, and this is the part of the category people most often get wrong on the first try.
| Product | Type | Rated figure |
|---|---|---|
| Solis Tek C1 315W CMH | Complete fixture, 120/240V, 3100K | Lamp included |
| Dutch Lighting Innovations CRI-Series | Fixture, 120V–347V | — |
| iluminar CMH 315W | Fixture | — |
| Endomaxx 315 CMH | Luminaire system, UL listed | 38,700 lumens |
| Endomaxx 150 CMH | Luminaire system, UL listed | See listing |
| Prism Lighting Science 315W | Remote ballast, 120–240V | — |
| GrowLite 315W electronic | Ballast, 120–277V | — |
| GrowLite 315W SE mogul base | Lamp, 4000K, mogul socket | 32,000 lumens |
| GrowLite 315W double-ended | Lamp, DE | 28,500 lumens |
| SunPulse 150W CMH | Lamp, 3200K | — |
Ballasts in this wattage class behave similarly to one another, which is the reason we tested lamps rather than ballasts. Your measurable differences come from the bulb.
Which One to Choose
Four situations cover most rooms running 315W CMH.
- Highest output from what we stock. The SunPulse 3200K, which placed second overall and first among lamps still available.
- Most UV within the class. The Ushio HiLux Gro 3000K at 8.6, the highest reading of the ten.
- Best colour quality to work under. The Ushio 4200K at CRI above 95, if scouting and plant inspection matter to you.
- Starting from nothing. A complete fixture such as the Solis Tek C1, which arrives with a 3100K lamp, removes the socket and ballast matching problem entirely.
3100K or 4200K for flower?
Our data gives a clear answer on output: the warmer lamps measured higher PAR across the board, and the top three positions all belong to the 3000K to 3200K group. If flowering output is the priority, that is where to look. The 4200K lamps earn their place in veg, in rooms where colour rendering matters, and for growers who prefer the whiter light to work under. Plenty of people run 4200K through veg and switch to a warmer lamp for bloom, which the spectral charts support.
If you are weighing CMH against other technology entirely, our guide to LED spectrum types covers what has changed since this test ran, and the lighting calculation guide covers sizing a room properly.
Frequently Asked Questions
The questions we get asked most about 315W CMH, answered from the test data where it applies.
What is the best 315W CMH bulb?
In our test of ten lamps the Philips MasterColor 3100K produced the highest PAR total at 10,678. We no longer carry it. Of the lamps still available from us, the SunPulse 3200K scored highest at 9,971.
What area does a 315W CMH cover?
We measured meaningful output across a 5′×5′ footprint, though intensity falls off toward the edges. A single 315W lamp suits a 3′×3′ flowering space or a larger veg area. Growers commonly treat one 315W CMH as comparable to a 600W HPS for spread, with considerably less heat.
Is 3100K or 4200K better for flowering?
For measured output, the warmer lamps won: every lamp in the 3000K to 3200K group except one outscored the 4200K lamps. The 4200K spectrum is broader and whiter, which suits veg and makes plant inspection easier.
How is CMH different from metal halide?
The arc tube. A CMH lamp uses sintered alumina ceramic that holds above 1200 K; a standard metal halide uses fused quartz. The ceramic tube resists the ion migration that shifts colour and costs output as a quartz lamp ages, which is where CMH gets its higher efficacy and colour rendering.
How long does a CMH bulb last?
Ceramic metal halide lamps are rated up to 24,000 hours, considerably longer than standard metal halide. Output still degrades over life, so most growers replace on a schedule tied to harvests rather than waiting for a lamp to fail.
Do 315W CMH lamps produce UV?
Some, as a by-product of how the arc tube makes light. In our 250 to 400 nm readings the ten lamps ran from 6.0 to 8.6 on a relative scale, with the Ushio 3000K highest. These are small numbers next to PAR, so treat the UV as a bonus rather than a reason to choose CMH.
Can I run a 315W CMH in my existing HID fixture?
Usually not without help. These lamps are physically small and do not use the mogul base most HID reflectors expect, so you need a purpose-built 315W fixture or an adapter. The GrowLite 315W single-ended mogul base lamp is the exception, built for a standard socket.
Does the ballast change the results?
Not enough to matter in this wattage class, which is why we held the ballast constant and varied only the bulb. Your measurable differences come from the lamp.
Is CMH still worth it compared with LED?
LED has taken most of this ground since 2016 on efficiency per watt. CMH still appeals where colour rendering matters, where a grower wants a single-lamp solution with a broad natural spectrum, and where the upfront cost of a comparable LED is the constraint. If you are building a room from scratch today, compare both on photons per watt before deciding.
The Bottom Line
The most useful finding is the one that only becomes visible once the numbers are published: the gap between the best and worst lamp in this test is under 16%.
That is a narrower band than the marketing around these lamps implies. It means a grower choosing on colour temperature, on fixture compatibility or simply on what is in stock is not giving up much, and it means the difference between a good 315W CMH setup and a poor one is mostly in the fixture, the mounting height and the room, not in which box the bulb came in.
Where the lamps do separate clearly is UV, with a 43% spread from top to bottom, and colour rendering, where the Ushio lamps stand apart. Those are the two measurements worth choosing on.
The test itself is nine years old and we have said plainly which lamps have left the catalogue since. The measurements have not changed, and neither has the method: one rig, one variable, every number published. If you have questions about any of this, give us a call or send an email. This is Nate from Growers House, happy growing.