What happens to Spectrum when we dim our lights?

[Greengenes707]

excellent info

are the wattages listed accurate or "nominal". in other words, due to voltage differences is it possible that "600W" could be 580 with one bulb and 630 with another?

It's gavitas testing...not mine.

It says "lamp power" and gives what look like generic settings from a dimmable ballast.
I would assume they put all bulbs on the same ballast(maybe the DE had a 400v version)...dimmed and tested accordingly. And then calculated based on stated "lamp wattage. Small fluxations are probably there. My take is the test is more to show what you are getting out of a "lamp x,y,z" on a 1000w ballast. And the ballast/auxiliary losses are considered "same playing field" or "equal", sonnot mentioned or factored in. We see that loss/effect when the full fixture is tested in test like bugbee's and others.

 

[PilouPilou]

View attachment 4019893

Hi! Do you think it's the same with a LED light?

 

[Greengenes707]

Hi! Do you think it's the same with a LED light?

It's the opposite. Full power on an LED will be its least efficient point. As it's dimmed it increase in efficiency/efficacy. At one point at very low dimming(like <25%), driver inefficiency can make it level out on the system level. But for all intents and purposes...LED lights(full systems) will get more efficient as dimmed.

 

[CobKits]

It's gavitas testing...not mine.

are only the top 2 bulbs DE?

 

[VegasWinner]

Hi! Do you think it's the same with a LED light?

It depends on the led light. If the light is designed to be driven in the efficient range changing resistance will not change the circuit dynamic as the relationship will remain the same no matter the level of amps applied to the circuit.
All leds are not equal as all hps are not equal. More specific the question the more specific the answer.

 

[wietefras]

are only the top 2 bulbs DE?

Whazzup posted this chart at the time when Gavita just introduced their DE fixture. The second line is Gavita's own 1000W SE bulb.

:edit: In another (Dutch) post Whazzup also states that dimming will shift the spectrum to blue and that you should first run the bulb at 100% for a few weeks to stabilize it.
http://www.wietforum.nl/topic/91303-gavita-pro-1000w/page__view__findpost__p__1009015

 

[waynejohn]

Dim the light, volume on max, full screen, press play

 

[OneHitDone]

While as in typical fashion for this section most are sitting around guessing at shit - here is what a lighting manufacturer has to say about dimming hps lamps:

http://www.eyehortilux.com/blog/post/to-dim-or-not-to-dim#continue

 

[MichiganMedGrower]

While as in typical fashion for this section most are sitting around guessing at shit - here is what a lighting manufacturer has to say about dimming hps lamps:

http://www.eyehortilux.com/blog/post/to-dim-or-not-to-dim#continue

Thank you. I was going to post that.

Just to add. Sun system says the dimmer on the galaxy ballast barely hurts the spectrum. Cmh stays balanced.

But I haven't found a reason to dim a 315 watt bulb yet.

 

[wietefras]

While as in typical fashion for this section most are sitting around guessing at shit - here is what a lighting manufacturer has to say about dimming hps lamps

Too bad those charts in itself don't show anything useful. We need a relative change. Besides, COBkits already posted one of those.

Gavita says that the small spectral shift towards blue could actually beneficial since you would normally only be dimming during veg and then the plants could use a bit more blue.

That HPS and MH bulbs lose efficiency when dimming is common knowledge. However, the advice on the bottom of that link is wrong or outdated on that point also. A Gavita Pro 750 does run more efficiently at 600W than a 600W SE fixture at 100%.

 

[Prawn Connery]

Why is the sky blue? Because shorter wavelengths (blue, UV etc) are more susceptible to atmospheric scatter, otherwise known as "Rayleigh scattering".

Longer wavelengths, such as far red and infra-red, have greater penetrating power. So it is no surprise that spectral measurements differ depending on distance from light source in any atmosphere. (Which, in fact, they do.)

Does voltage affect CCT in LEDs? I'm certainly no expert. But on every spec chart I've read, yes voltage does affect CCT shift - the lower the voltage, the lower the CCT; the higher the voltage, the higher the CCT.

Samsung F Series datasheets show the 5000K strips produce 4798K at 43.7v, 4984K at 46.0v ,and 5177K at 48.4v Other CCT strips show a similar pattern.

Why? Well, perhaps the answer is as simple as thermal radiation - the hotter a metal, the higher the "heat" colour (Kelvin). This is certainly true of HIDs. When you dim them, they go redder because they are running cooler. It's like the red glow of a HPS when you turn it off and it immediately starts to cool down; or the transition from red to yellow when you first turn the lamp on and it starts to heat up and stablise to operating temperature.

LEDs give off heat - the higher you drive them, the more heat is given off - so there's no reason for me not to believe the pn junction metals and reflective surface within the LED give off a higher thermal radiation temperature as they get hotter.

That would be my understanding.

 

[PilouPilou]

It depends on the led light. If the light is designed to be driven in the efficient range changing resistance will not change the circuit dynamic as the relationship will remain the same no matter the level of amps applied to the circuit.
All leds are not equal as all hps are not equal. More specific the question the more specific the answer.

I am a DIY COB user..

 

[jonsnow399]

"thank you for your question.

Dimming the the bulb for extended periods will indeed reduce the lamp life but it is negligible. Before you dim or boost your HPS lamp, make sure that you run it at nominal value (100%) for at least 100 hours to stabilize the lamp. Failing to do so may lead to sub-optimal light levels and premature end of life failure of your lamp.

I will ask my colleague for a file where you can see the changing in spectrum.


We recommend changing your lamps and reflectors ones a year, if you keep to this schedule you will have a constant high output of high quality grow light.

Feel free to contact us if you have any additional or other questions.

Best regards, met vriendelijke groet,

Roy Voordouw" Gavita rep FWIW

 

[MichiganMedGrower]

Too bad those charts in itself don't show anything useful. We need a relative change. Besides, COBkits already posted one of those.

Gavita says that the small spectral shift towards blue could actually beneficial since you would normally only be dimming during veg and then the plants could use a bit more blue.

That HPS and MH bulbs lose efficiency when dimming is common knowledge. However, the advice on the bottom of that link is wrong or outdated on that point also. A Gavita Pro 750 does run more efficiently at 600W than a 600W SE fixture at 100%.

There was a video a few years back before the harts posted. The blog did not say but I am pretty sure it is for single ended lamps only.

 

[CobKits]

Too bad those charts in itself don't show anything useful.

it actually tells you a fair amount if you look at the efficiency numbers below the graphs

hps loses 20% of its umol/J at 50% - not ideal to dim bout doable
mh loses 50% of its umol/J at 50% - never good to dim

 

[VegasWinner]

I am a DIY COB user..

What did you design towards regarding drive amperage? With 36v cxb3590 I believe the optimum drive current is 700mA or so, not sure the exact number, lower than most folks drive them.
I used a drive current of 700ma for36v cbx3590 and got excellent results. Used a 185h-c700b driver I never had to dim.
That is my approach. Look for the optimum drive current to get the highest umoles per watt and design to that. Ideal Current varies by cob and manufacturer.

 

[wietefras]

There was a video a few years back before the harts posted. The blog did not say but I am pretty sure it is for single ended lamps only.

It's a chart dated 2011 and Whazzup posted it end of 2011 on Opengrow when they were introducing their DE fixture.

The first line is the DE bulb.

 

[wietefras]

it actually tells you a fair amount if you look at the efficiency numbers below the graphs

hps loses 20% of its umol/J at 50% - not ideal to dim bout doable
mh loses 50% of its umol/J at 50% - never good to dim

I was looking more at the spectral distribution charts. It's hard to read let alone compare them like that.

The Gavita bulb measurements which Greengenes posted gives a better indication of what dimming does for efficacy for the bulb in use. The Hortilux in that comparison is actually one of the bulb which suffer most from dimming.

 

[OneHitDone]

I was looking more at the spectral distribution charts. It's hard to read let alone compare them like that.

The Gavita bulb measurements which Greengenes posted gives a better indication of what dimming does for efficacy for the bulb in use. The Hortilux in that comparison is actually one of the bulb which suffer most from dimming.

This post is about spectrum and dimming, so charts are relevant.
To say that the chart is "outdated" and as many say SE HPS is "outdated" is just not being honest. The truth is SE HPS will still be producing truck loads of dank long after the cobs most of those on this site are using have made their way to the recycling scrap pile behind Fry's Electronics

 

[CobKits]

With 36v cxb3590 I believe the optimum drive current is 700mA or so,

what makes that "optimum"?

500 mA = more efficient
900 mA = more cost effective

saying a certain current is "optimum" seems arbitrary