Supplement HPS with LED's to round out spectrum?

fire-stick

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I have been thinking about this for a while and decided to brush the dust of my CPF username and see what you all thought. I know this would be largely redundant with the advent of cheap, full spectrum LED's, and even partially so, with fuller spectrum MH and CMH lights, but I was just wondering. What type of LED's, and what size, (wattage), would be needed, to add to, say, a ring around the HPS fixture, to take a 20ish CRI, 250 watt, 2200 K HPS light to a daylightish temp, high, (75+ CRI) light? I know, obviously blue would be needed, but that's about where my little brain looses steam. ANY thoughts??!!?? Would the LED's be the monochromatic type with just one number, (like 500nm), or would they have to be a full spectrum colder temp like a 6500k?
 

mattheww50

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I think you are in for a very rough ride. The All HID lamps including HPS lamps run at very high temperatures because basically you have an arc inside, so keeping the LED's cool in the same fixture is going to be a real challenge regardless of wattage of the LED's.Also keep in mind that most HID lighting is fairly efficient, often approaching 100 lumens per watt in the larger lamps, so the LED wattage is likely to end up in the range of 70-80% of the HID wattage. Some of the LPS lamps (which have absolutely horrible color rendition) exceed 200 lumens per watt.
 

fire-stick

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I think you are in for a very rough ride. The All HID lamps including HPS lamps run at very high temperatures because basically, you have an arc inside, so keeping the LED's cool in the same fixture is going to be a real challenge regardless of the wattage of the LED's. Also keep in mind that most HID lighting is fairly efficient, often approaching 100 lumens per watt in the larger lamps, so the LED wattage is likely to end up in the range of 70-80% of the HID wattage. Some of the LPS lamps (which have absolutely horrible color rendition) exceed 200 lumens per watt.

Yea, I wasn't really planning on building one I was just wondering. I watched a video earlier that was kind of along the same lines and the guy said most HPS don't have any cyan. I have heard of the color but not really any led's. You did bring up a good point about the efficiency though. It's hard to believe that HID's have been around for so long and still have such a high efficiency.

I was mostly thinking about HPS grow lights and how they have such a narrow band and why no one has come up with a circular type think that would go around the HPS but there is probably a good reason no one has come up with such a thing, probably due to some of the hurdles you mentioned above, amongst other.. Either way, it was just something I was batting around in the old grey matter. Appreciate your reply.
 

JoakimFlorence

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Jun 4, 2016
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I don't think LEDs would really round out the spectrum all that much. If there was a "complementary" effect, it would be very small.
What you'd probably get is a combined light with a CRI level between the two sources.
If you're talking about efficiency, you would be much better off combining LPS with LED.
The whole point of the development of HPS was to raise the CRI a tiny bit over LPS, whose light is nearly monochromatic, but it comes with a substantial tradeoff in efficiency.
From an engineering standpoint, there'd be no point in using HPS if you were combining it with LED. (HPS + LED is almost not going to give any spectrum advantage over LPS + LED)

The primary yellow-orange spectral line in sodium vapor is not going to give you any spectrum improvement over an ordinary 2700K LED.
 

Ken_McE

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Jun 16, 2003
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What you are describing is technically possible, but I can't think of a market for it. HID bulbs are all about pure brute efficiency, not CRI. If you built an add-on ring it would have to have an air gap between it and the HID lamp, its running gear, and its housing. You would need to change the size and strength of the ring to adjust it to every different fixture. Dozens of models in return for what?

That being said, at the least you would need to add green and blue to a Sodium spectrum. The HID Sodium bulb would produce around 33,000 Lumens, which would take a lot of LEDs to match. I don't know if the natural orange of the Sodium could serve for red. If not, add red too, and now that you have an RGB LED light, that produces almost 100,000 Lumens, what do you need the HID part for?

If you want to start with HID, and CRI is a concern, consider starting with a Multi-Vapor Metal Halide. They have almost the efficiency of Sodium or Mercury HID, and a much nicer spectrum.
 

broadgage

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Adding suitable LEDs to a HPS fitting could be done but would add considerable cost and complexity for a modest gain in colour rendering. A possible advantage would be that the LEDs would stay lit when the bulb burns out. Reduced light of an odd colour would be better than no light, in most circumstances.

I very much doubt that the idea is worth pursuing however. HID lighting is a dying technology that is increasingly being replaced by LED for greater efficiency, better colour, and longer life.

Before the LED age, Phillips lighting used to sell a large floodlight fitting that used two lamps, each of 400 watts. One was high pressure sodium and one was metal halide, the combined light had good colour rendering, pleasing color appearance and modest running cost. If desired, the two lamps could be controlled separately so as to give a reduced lighting level of poorer quality at times of low usage.
 
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