Fall 2019 we cando to we wavelengths add light of filters: take they light away.There’s nothing firstThe thing to realize isthattheseare Theory usingthem? advantages anddisadvantages of H wheel), which improves thecolor rendering. (either asaseparate filter or on the color manufacturers now offer adrop-in filter filter. automated Quite a light number of filter,of a color rendering enhancement stimulated anew kind thedevelopment of powerful white LEDsourcesthe useof has is about. What Ido findinteresting isthat one day, switch over to additive mixing. sustainable ortechnology. lasting We must, is king, but you can’t convince meit’s a for those users tooutput white whom light there are reasons good for this, particularly using subtractive color mixing. source, then throw by away thelight mostof use them to make amediocre white light excellent additive mixingsources, but instead that we don’t LEDsas usethestrength of anomaly.transient It to just seems crazy me dichroic subtractive color mixingto a be usingwhite LEDswith current trend of know thatIconsiderin thepastwill the of youThose have who read thiscolumn Color renderingenhancers Out ofthe Wood light away.“ light is thattheseare filters, take they thing to Thefirst realize ow do thesefilters work,what are and the H owever, that’s thiscolumn notwhat “ BY Mike Wood Y es, Iknow a narrow blue spike from theLEDalong phosphor. result net The isasseen here, atranslucenttopped broad-yellow with a blue pump LED 7,000 Kwhite LEDwith phosphor-converteditself. isatypical This Top-left (theblue isthewhite LED curve) each graph. of the left andred on theright different wavelengths, blue wavelengths on thesystem shows at chart theoutput of asitgoes through thesystem.the light Each power (SPDs)of distributions the spectral view.a theoretical pointof beam. Figure from 1 shows story thewhole those thatare already present inthelight don’t have, but of we canadjust theratios The four curves shown here shown fourThe curves represent Fall 2019 20 Figure 1–Colorrendering enhancertheory more like thedaylight. Mathematically filter that convertswhite the LEDto acurve do we from get one to theother? We a need by definition, perfect color rendering. H the samecolor temperature, 7,000Kand, reference source, inthiscase adaylight of (thered curve),right we have ourperfect be. asitmight is notasgood Next, attop- in thecyan meansthatthecolor rendering missingenergy of reds andthevalley lack of together theeye thisasawhite. sees The abroad yellow/greenwith hump. Taken

“ . . . there’s here. nomagic ow “ Fall 2019 Color rendering enhancers rendering | Color Figure 2 – LED source SPD 2 – LED source Figure Figure 3 – LED source color rendering 3 – LED source Figure Out of the Wood Wood of the Out show the same source with a #3308 Minus Green with Green a #3308 Minus the same source 4 and 5 show Figures I’m including CRI Ra values here as a link to the past, you should not not should you the past, including as a link to CRI Ra here values I’m it just of rendering color be using CRI as a measure LED sources, for of a lot history forget to here. there’s I know Nevertheless, work. doesn’t in this article the CRI values with a large pinch of salt and just Take TM-30.) at the look and the expected, as The SPD curve has been flattened place. in filter TM-30-15 Rf a Rg of have we 85, Now up. has gone rendering color Light improvement. a noticeable Quite and CRI Ra ofof 89.5. 104, What’s about 63% of to down the original. has dropped output can spike, blue a large still is that we have noticeable immediately is spike a blue reduce to that? The way reducing stillbetter by do we yellow. a withof a filter complementarycolor, the 21 L PROTOCO ekonic C-800 ekonic o, we can essentially divide the result we want to achieve achieve want to we can essentially divide the result we o, ow much dimmer? In this extreme example the filter the filter example this extreme In dimmer? much ow owever, these graphs are very misleading! I rescaled all four these graphs very all four misleading! I rescaled are owever, What do these filters look like, what color are they? Looking at they?Looking at are color what look like, these filters do What H owever, there’s a problem. We know we can’t add wavelengths we we add wavelengths can’t we know We a problem. there’s owever, o, job done. job o, PDs and TM-30-15 color rendering rendering SPDs and TM-30-15 color can measure which meter, book placed swatch with the filters Rosco was a filter and my index, an the starting 2 and 3 show point, Figures sensor. the meter across The with light 6,100 K white a typical source SPD. approximately is still very there but source, theoretical valleycyan was less than my as measured rendering The color light. red little long-wavelength a TM-30-15 Rfhaving and Rg of of 94 and a CRI Ra of 82, 82.5. (Note: see if better. can do we let’s but a horrible lightNot source, Practice was a LED light a white source set-up was very test simple, My was a S the detector workshop, lightwork in my the process is straightforward: filters is straightforward:act spectraon filters multiplyingthe process as S factors. 23% of the light to a 77% loss. output reduces the original value, the manufacturers Instead, be acceptable. to much too That’s of what decide level light loss approach, an intermediate take will It accordingly. design and then the filter is acceptable, in color be a trade-off improvement much always how between Most it. the light achieve lost to versus is achieved rendering with and 25% loss be working to seem around manufacturers extra points of more or color five around them gives which rendering. a pretty good can take we 1 curve in Figure Filter the Correction attenuates but redblue and through allows which a filter It’s guess. Reduce filter. magenta be a pink or to going It’s and yellows. greens the saturationreducing and lettingbit more a by losses the filter a very to close likely get a pale magenta, light and we’ll through do could if filter green a minus Okay, filter. minus-green standard the theory! test let’s this, by the light we have and the result will be the filter that’s required. required. will that’s and the result be the filter the light have by we H dividing a to be mathematically equivalent That would have. don’t the pick need to we Instead a bad and that is thing. zero, by number and still try let some to going are and correct, that we value lowest That to 20%. limit the filter to this case I chose In light through. of some out It cuts curve). (green is shown at the bottom-left filter through allows and hump, the green/yellow reshapes spike, the blue is shown result bottom-right The final as is available. red as much Still missing the broader. much is now The output (purple curve). (pale the reference matches the curve in the center but and red, cyan rendering. color better in a much This results curve) pretty well. red S comparison make the vertical axis to on one to be zero SPDs to a lot of the removes the filter in actual fact, whereas, easier, light than the original dimmer light and our output is much H LED. Fall 2019 that, primarily because of theblue reduction fromthat, of because the No primarily Color original, that’s but perhaps acceptable insome usecases. Note also acceptable. the isthattheoutput Downside isnow down at58%of points to 87,couple of Rgis98, is89.8. andCRIRa very All Figures 8and9. Minus Green andtheNo Straw intend to usethison itsown. Let’s the both we what with see get 77. of 80andCRIRa H reduced of down to anRf hump aswe expected. U beam. blue The spike isconsiderably reduced relative to theyellow justthe result a#06No with Color Straw paleyellow filter inthe Out ofthe Wood This seems to be working pretty well! TM-30 Rf isupanother seems toThis working be well!TM-30Rf pretty Let’s yellow on to itsown theeffect. see try Figures 6and7show Figure 5–LEDsource +MinusGreen colorrendering Figure 4–LEDsource +MinusGreen SPD nfortunately, color rendering isactually | Colorrenderingenhancers Y ellow inatthesametime. That’s owever, we don’t Fall 2019 22 output, which isprobably going too far. Compare Figure 10with them away. With thetwo filters inplace Iwas down to 42%light blues. deep reds and themissingcyan and lack of to goof because practical a littlebetter, that’s but Isuspect just aboutasfarit’s reasonably other manufacturer’sand tried aswellIcould gelbooks have done at5,636K. good CCT isalsopretty I’m I’d sure if played longer #4930LavenderStraw along with inFigures asshown 10 and11. 99, 91using a#06No 88,of of andCRIRa Color of TM-30 Ra Rf approach result best empirical very this Iachievedwasa with paleyellows magentas/minus green gelswith andstrawsof andthe Straw, ourCCTisreduced to 4,172K. I experimented for longer, awhile different combinations trying Y ou cannever missingwavelengths add filters, with just take Figure 7–LEDSource +NoColorStraw ColorRendering Figure 6–LEDSource +NoColorStraw SPD Fall 2019 40-year A 40-year Color rendering enhancers rendering | Color n Figure 10 – LED source + Lavender + No Color Straw SPD + Lavender + No Color Straw 10 – LED source Figure and Co-Chair of the Technical Standards Council. Mike can be can be Mike Standards Council. Technical A and Co-Chair of the Out of the Wood Wood of the Out As to the point of the article? Just to show that there’s no magic that there’s of show the point to to As the article? Just Figure 11 – LED Source + Lavender + No Color Straw color rendering Color Straw + Lavender + No 11 – LED Source Figure here and we are able to trade to able off to are rendering and we light color here for output designcould you In the same way filtering. suitable the needsuit by measurableor other spectral matching, TLCI, to maximize filters we and filters subtractive that these are forgetting Never parameters. lose light. will always C, which provides consulting which provides consulting Consulting LLC, Wood runs Mike Wood Mike support to companies within the entertainment industry on product design, and Intellectual Property. standards, R&D, technology strategy, is a past President Mike of the entertainment technology industry, veteran of EST reached at [email protected]. 23 L PROTOCO Figure 8 – LED source + Minus Green + No Color Straw SPD + No Color Straw + Minus Green 8 – LED source Figure Figure 9 – LED source + Minus Green + No Color Straw color rendering + No Color Straw + Minus Green 9 – LED source Figure There’s no real conclusion to be drawn here. This was an interesting This was an interesting be drawn here. to conclusion no real There’s using standard be done in seeing what could me, at least for exercise, Ifofrendering color LEDs. the white off-the-shelfto improve filters to the source, tailored filter a custom manufacture been to able I’d good color results: get better been possible to have it would then taken This is the approach with in output. less reduction rendering, using They are of light manufacturers. many the automated by suit their to with tweaks on minus based green, likely filters, dichroic specific lightengines. So what? , and you can see what an improvement can see what an improvement and you 2, Figure started, we where of in continuity made the spectrum. we’ve