r/lightbulbs

Its often said that violet pump white LEDs(WLED from here on) are superior and they are used in some of the best LEDs you can buy in terms of color rendering. Those include names like Soraa, Sunsy Shine, Yuji Sunwave and Waveform Absolute. In this post I will be using some jargon that was explained in my previous posts on CRI and CCT to keep this less than a mile long. Only new stuff will be completely broken down.

Most WLEDs use a 450nm visible blue LED coated with a phosphor that converts that short 450nm light into longer wavelengths, which is how they make white light. The underlying blue LED is called the "pump" LED.

This shapes the spectral power distribution(SPD) of many WLEDs to have a nasty spike where the blue light punches through the phosphor coating in excessive amounts. Cheap high color temp LEDs are notorious for this, and while the blue light is useless *glare* it still counts towards luminous efficacy! That's how some manufacturers cheat.

A violet pump WLED uses the same principle but shortens the wavelength of the pump LED to somewhere around 410-420nm, which makes it closer to the ultraviolet part of the spectrum.

I wondered what the advantage of this is beyond the usual marketing speak about "eliminating the blue spike". But there *are* some blue pump WLEDs with very low blue spikes like the Philips Ultra Def 2700K but not the new crappier 5000K, some Yuji, Waveform, Emery Allen etc. So why go to all the trouble i wondered?

Turns out there is another HUGE advantage of using violet pumps that gets almost no discussion. Real daylight *and* halogens/incandescents all include visible violet and some invisible UV in their spectra, in varying proportions. Incandescents produce less than halogens and halogens less than daylight.

Some materials will react to higher energy, short wavelength light. UV, visible violet or even visible blue light can make different materials *fluoresce*. They glow by reemitting the light that strikes them as a longer wavelength.

If the light that strikes them is invisible UV and you're in a dark room, the objects will appear to glow in the dark. However, the UV in daylight or even in halogen/incandescent bulbs is enough to make materials fluoresce! That changes the color and brightness that objects appear *when brightly lit as well*.

There is a huge, little known industry revolving around this phenomenon that produces chemicals called optical brightening agents(OBA) that they put in tons of things you see and use every day like fabrics, paper, laundry detergents and plastics of all kinds.

They are used to make white materials fluoresce a bluish color, which makes them look *whiter* since the OBAs in the clothing or paper reemitting bluish light which they convert from invisible UV basically shifts their white balance. This can counteract the natural, slightly dingy look of untreated cotton or paper, which often absorbs more blue than yellow making it look dingy. OBAs are added to laundry detergent to literally make the clothing fluoresce.

If you have a blacklight or ever played with one, you know your white clothing will glow and some laundry detergents will also glow vividly. They're also in tons of colored objects as well!

Blue pump LEDs can't make these OBAs fluoresce bluish due to physics: phosphor conversion can only take shorter wavelengths and convert them to longer ones. This is key. If the shortest wavelength the blue pump LED emits is already visible blue light, it can only make an object *reflect* blue light. Since the blue spike is undesireable, and since a lot of materials with OBAs added naturally absorb blue light more than longer wavelengths, cloth and paper or anything with OBAs added can look dull or dingy when lit by even very high CRI blue pump LEDs when compared to daylight or incandescents.

Not only are chemicals that fluoresce added to all sorts of stuff, but a lot of natural materials will fluoresce to some degree from specific regions of the visible violet to UV parts of the spectrum.

This finally brings us to the actual LEDs. A *violet* pump's SPD begins significantly closer to the UV part of the spectrum around 410nm, and therefore covers more of the entire spectrum than blue pumps which start around 450nm. That 40nm extra changes the overall shape of a violet pump WLED's SPD significantly, making it more like incandescents at 2700K-4000K and more like daylight at 5000K or higher.

That 40 extra nanometers of wavelengths also activates optical brighteners and natural fluorescent materials more like real daylight or incandescent bulbs do! That little discussed fact is actually a HUGE benefit of violet pump WLEDs!

This object fluorescence and "white rendering" is not taken into consideration properly by CRI or TM-30. The only real way to account for it is to examine the SPD of a light source.

Its a bummer that the high CRI violet pump LEDs are so expensive. A single A19 60W equivalent is about $25 at a minimum. So 10x a blue pump 95 CRI or 100 CRI incandescent/halogen.

Pretty much any LED is super efficient, but violet pumps are among the least efficient as well, so with stupid overregulation of consumer light bulbs, its likely to stay a niche product.

All of the acronyms or jargon used were covered in plain English here:

https://www.reddit.com/r/Lighting/comments/1rzviiw/a_primer_on_spd_cct_and_duv/

Appendix:

I should probably clarify a couple of things, maybe more.

The fact that these violet pump WLEDs include some violet light in their spectrum is neither harmful or intended to make objects visibly glow in the conventional sense.

Real daylight and incandescent bulbs both include UV and violet light in their spectra. For incandescents the amount of UV in relation to their overall light output is tiny. Its more with daylight but still not a large portion of its actual light is in UV on earth, due to the atmosphere filtering out all UVC and much of the UVB and UVA, as well as some of the visible spectrum. Hence, daylight's lumpy but not spiky SPD graph at any CCT in its wide range.

Similarly, violet pump WLEDs include some violet(no UV) and its a tiny amount in relation to their overall output.

The violet light in real daylight and incan/halogen will cause objects to fluoresce or glow, but it doesnt look like the kind of thing you'd see in a dark room with a blacklight as the only light source at all. The fluorescence of objects under daylight, incan/halogen or violet pump LEDs manifests as bright white clothing and paper, or vividly colored paint, plastic and glass which have OBAs added or have nautral fluorescence in their chemical makeup.

So its more that a tablecloth or sheet of paper will look crisp bright white under daylight, incan/halogen or violet pump LEDs without a dingy or dull appearance that may happen with even a very high CRI blue pump LED.

The main drawback to violet pump LEDs is their low luminous efficacy as i mentioned, which also means for a given luminance they generate more heat, which is bad for LEDs and they typically need big expensive heatsinks compared to blue pumps.

For comparison, a 60W incandescent has a luminous efficacy of 13 lumens/Watt. A blue pump 60W equivalent is usually between100-200 lumens/Watt. While a violet pump is about 60-70 lumens/Watt.

The violet pumps are still super efficient compared to incan/halogen but much lower than even the least efficient blue pumps.

Hey all.

Can anyone confirm that this connection is incorrect? Questioning it because I don’t know much considering this is my first time replacing headlights, but it plugs in perfectly.

Thanks