Why do some want high CRI?

Discussion in 'LED and other Lighting' started by disengaged, Oct 6, 2015.


    disengaged Member

    I'm a little confused about the desire of some to build lamps with a high Color Rendering Index. Isn't CRI simply a comparison to how "normal" colors appear under it?
    Plants don't use the same spectrum as the human eye to grow, so just because the light may not render colors in a way that is pleasant / familiar to the human eye it has little to do with what plants need for photosynthesis.
    I'm not going to argue against the discovery that some "multi-color" and perhaps "full spectrum" LED lamps may produce less than ideal results - it seems the forum members here have proven more "white" was needed than scientists and lamp builders had thought. On that subject I might guess the designers were not accounting for the relatively insane amount of light used for "flower production" in comparison to growing lettuce. It's been a year since I spoke with my local retailer, but in reference to the expensive light bars he phrased the benefit of switching to newer (at that time) LED bars as superior "oil production".

    High CRI, that's what I'm searching for when I shop for LED's to replace the tungsten / CFL lights around the home. It is not what I'm searching for in a light for plant growth.

    The most beautiful, and heaviest flowers I've seen were those along the edge of a MH lamp's coverage area, surrounded by HPS on either side. Heavy as in a Grapefruit (dating myself to the last century) cola the size / shape of an American football, but such flower clusters would often rot from the inside out from mold growth before harvest which sucked. Not just the Grapefruit strain, but others which made large diameter / dense colas. The beautiful growth an indication that neither HPS / MH was a perfect spectrum on its own.

    Yes, I'm new to LED's... but is there a reason for high CRI? Have the light spectrum of these been measured to indicate it is better for plant growth, observation of certain qualities, etc... ?

    If my cabinet is raided you will find basil and lettuce and would really prefer to avoid the stress of having my door smashed in and possibly being shot... because that would suck for everyone.

    hyroot Well-Known Member

    Higher the cri. The more even the spectral output.
    alesh likes this.

    ttystikk Well-Known Member

    No, just better values relative to sunlight.

    ttystikk Well-Known Member

    I'm getting 80 CRI chips. I'm running 860W CDM lamps at the moment. One reason I chose them was their 92 CRI. Now, if high CRI did anything for plant growth, they'd outperform HPS thouies which clock in at only 22 CRI. They do not. Therefore, high CRI is nice for growers and photographers, but the plants don't seem to care.
    testiclees, PetFlora and churchhaze like this.

    disengaged Member

    Has this been verified with a spectrometer?
    When you state "The more even the spectral output", is the spectral output in the range of what benefits photosynthesis more than visual appeal?
    These lights are designed for producing "good looking" light, not for the spectrum the plants may need. Maybe my point is "does it benefit the plant, either from increased rate of photosynthesis - or more compact plants, higher yield of flowers, higher yield of resin, increased THC / CBD content... more nutritious vegetables...

    The earliest LED (tungsten screw in replacement for lamps) had poor CRI when dimmed - I think reviews said the light became blue. If we are not running our COB's at full power, then are they dimmed?

    Curious, not attacking, just want to understand.
    testiclees, anzohaze and ttystikk like this.

    ttystikk Well-Known Member

    COB LED does not significantly alter spectrum when dimmed and they do emit light more efficiently. These are the reasons why running them 'softly'- that is, at a fraction of their full rated output- is so popular amongst growers.

    Example; CXB3590 COB LED CD bin 3500k

    Run it at 100W, it returns about 45% efficiency.
    Run it at 50W, efficiency climbs to 56%.
    Run it at 23W and efficiency climbs to 64%!

    The drawback is cost; the chips cost about $50 apiece right now so to get the efficiency improvements, one needs to spend twice or four times as much up front on chips.

    The term 'Dimming' in the LED boards does not refer to this practice of under driving the chips; rather it refers to a dimming pot in the circuit. I honestly don't know how those affect efficiency and I'm as curious as you about it.

    SupraSPL Well-Known Member

    Hi CRi leds (~95 CRi) have a more even spectral balance and they have a larger percentage of their output in the deep red range where human vision response is low. It is a slightly more photosynthetically efficient spectrum BUT it comes at a significant cost to efficiency. 70-80CRi LEDs seems to be a good compromise point of very high efficiency, good output in the red/deep red range and high efficiency.

    To make matters worse for the high CRi option, we do not currently have access to top bins of the high CRi but we do have access to the top bin 3000K and 3500K 80 CRi.

    The curves have been adjusted (thank you @MrFlux ) so they are truly relative to each other in terms of flux, assuming top bins of each.
    CXA spectral flux mod.png
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    alesh Well-Known Member

    Mouser actually expects a batch of the top bin (BD) 3000K/90CRI CXB3590 at the end of October. The price is terrible but they should match their lower CRI counterparts in efficiency. All the data and the design are stolen from your spreadsheets :)
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    SupraSPL Well-Known Member

    Awesome data and graph thank you Alesh! It might be fun to take wagers on the date Mouser will get them hehe.

    alesh Well-Known Member

    When I look at the prices of CXB3590s at Mouser, I guess they could be quite decently priced at Kingbrite had they been able to get them.
    SupraSPL likes this.

    disengaged Member

    That is awesome data!
    Are those the $88 chips or higher?
    Guess it is an ask and receive... in middle of writing a post in the "help choosing led" thread, near post #7000
    Is there similar info for those of us who can only afford Vero COB's?
    Anything compelling enough to make one buy currently available 3070's even if she whom must be obeyed cringed at the up front cost, still tried to justify the energy savings...

    alesh Well-Known Member


    ttystikk Well-Known Member

    Two ways to justify the upgrade to COB LED;
    1. Reduced operating cost, more efficient, less waste heat, no more replacement bulbs, great spectrum, blah, blah, blah
    2. MORE YIELD. Pays for itself in additional yield on the first run, assuming the grower (ahem) doesn't bugger it up.

    Should get the go along somewhere between those two.
    bicit likes this.

    OneHitDone Well-Known Member

    Have you tested 1000W's of CDM against the 1000W hps?
    Where do the 860 CDM's come in in yield vs a 1000W hps?
    ttystikk likes this.

    HiloReign Well-Known Member

    The god of CRI is appeased at the use of high CRI lighting.

    coolbreez1 Well-Known Member

    Higher CRI does make it easier to diagnose plant health. It also makes the plants look much more impressive when people that are used to looking at them under HPS take a gander :)
    ttystikk, OneHitDone and alesh like this.

    disengaged Member

    Thank you
    Different scale? Even if so, can try to draw conclusions. Am I mistaken or is that a slight edge to the Vero's in the red spectrum? Had to print them out in B&W and use my strongest reading glasses. ... No, got that backwards... Cree actually has better spectrum and efficiency?
    You are killing my wallet.
    Still telling myself I'm not going to spend today shopping for COB's...

    and the previous two posts made me laugh...
    Last edited: Oct 7, 2015
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    alesh Well-Known Member

    The scale is the same [W/nm]. But it's absolute output [email protected] vs [email protected], not a very fair match.
    However, the units on the vertical axis of the chart in post #8 are wrong. There should have been [W/nm] instead of [┬Ámol/s/nm] and it it's rather radiometric flux than photon flux. The values are correct, though.
    bicit likes this.

    ttystikk Well-Known Member

    Right about the same g/w, so slightly less bulb for bulb. Quality is noticeably and consistently better, however. I'd expect the 315W version to yield more per watt due to its digital square wave ballast.
    anzohaze likes this.

    ttystikk Well-Known Member

    Yes but when my plants prayed before the munificent 92CRI of 860W CDM for eight weeks, the number on the altar showed no improvement in the all knowing g/w calculations...

    The high intensity discharge priesthood is conferring even now on the portents of this development.
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