Something you need to realise about our perception of colour is that when we see a reddish or bluish colours (such as the sunset or a blue sky) the spectrum that we are seeing is actually broad band and contains all visible wavelengths with just a 'slope' over the spectral band. Blues and reds are seldom removed from any common light source - except for monochromatic sources and suitably driven TV displays.renault said:
Could you post the spectra from a couple of your LED light bulbs in your home, along with their ratings (power, "warmth", etc.)? That would be interesting to see...sophiecentaur said:
The device is very small and works well when you put your eye right next to it - very impressive in fact. But I never go round to fixing it securely enough to take a photo image.berkeman said:
Afaik, domestic lighting bulbs start with a UV source which passes through a mix of phosphors to produce any spectrum they want. If you're talking about the 'false filament' lamps thenrenault said:
berkeman said:
Interesting. If you were to try to get good matches for two different 'strongly' coloured cyan fabrics (i.e. blues and greens reflected by the dye and a cyan dye for the other fabric) then you could risk seeing a mismatch when you get home or go outside where the illumination is uniform. Time was when people would take coloured clothes outside the shop to see what they would really look like. Those horrible flu tubes were very popular in department stored. Incredible spectra! I believe the M&S women staff used specially chosen makeup to make female customers feel inadequate and needing new clothes and makeup.pinball1970 said:
renault said:
We are not talking about hot tungsten filaments. We are talking of the (used to be) fancy filament-look-alikes which have a string of leds with extras- see the link in the post above.f95toli said:
Not strictly true. The colour temperature achieved with a led device is artificial and a sort of match to a black body source. The low cost eastern manufacturers often think of a number ; a high number for blue-white and a low number for a warm white. In the old days, temperature meant temperature and was fairly easy to reproduce if you could rely on the voltage value.f95toli said:
you are absolutely right. All you can do is use (full price) led bulbs from just one manufacturer throughout a room or house if you want consistency. If you are into Feng shui then you have to use oil lamps.f95toli said:
Worth reading this study.renault said:
Virtually no UV in the commercial LEDs I've looked at. You can see that in the SPD I posted.Vanadium 50 said:
yes I remember being told that the meat counter in supermarket was illuminated with lower colour temperature bulbs in order to make the meat look more red. It is true - look down the isle of the supermarketsophiecentaur said:
This switch to LEDs is a huge energy benefit as we have discussed before. M&S used TL84 not sure if they still do CCT of 4000K.sophiecentaur said:
What problem?renault said:
Of course. You can make a 'white' illuminant that has massive holes in its spectrum which will match (metameric) a hot filament (black body). Narrow band pigments could appear almost black if they fall in the holes. It's important to distinguish between analysis of colours and synthesis.pinball1970 said:
Haha - to add further confusion to the discussion. In the context of regular colourimetry, the illuminant is assumed to be a black body. When it's not we have a different can of worms. I imagine the mqarketing of 'high quality' lighting (as used in surgery and printing) could risk being like the HiFi trade)pinball1970 said:
Yes we have had a discussion on this too and that's when you demonstrated, reflectance data on a surface is not the same as discussing a black body.sophiecentaur said:
As far as I am aware, there is no good evidence that blue and violet light has negative effects on people, including sleep disturbances and macular degeneration. There's an immense amount 'information' that gets tossed around when it comes to health, the vast majority of which is nonsense. Combine that with sensationalist news articles and people jumping on every new fad that pops up and you get an environment that highly susceptible to misinformation, fearmongering, and exaggeration.renault said:
Because then they wouldn't have white lights. They would have orangish lights.renault said:
You can't eliminate blue light if you want to achieve white light. You're going to need at least some.renault said:
That's your choice, but be aware that one can never prove the health effects are zero. If there were health effects for one person in a trillion, would we ever know? There aren't a trillion people. There have never been a trillion people.renault said:
You are free to believe whatever you'd like and to take whatever steps you'd like. But if you come here to PF and ask what steps you can take to protect yourself, you have to accept that we can only give you advice that is based on mainstream literature (or at least our understanding of it). Since that literature doesn't appear to clearly support the idea that blue light is harmful, nor that some protective measures like blue-light blocking glasses are even effective, you cannot fault us for saying so.renault said:
That's exactly right.renault said:
No, but there is one between color temperature and color. The reason there isn't one between color temp and wavelength is that, on the whole, many different combinations of wavelengths can generate the same color. This is why the red, green, and blue pixels on your computer of phone screen can generate yellow, orange, and other non RGB colors.renault said:
They are indeed marketing descriptions but they are not without validity. The CIE ( "Commission Internationale de l'éclairage" ) color response curves are attempts made in 1933 and 1964 to characterize a standard human's vision and color response. Within that context, the meaning of color is pretty well defined. All humans may not percieve colors this way but the majority will, and the system provides a useful, but not unique, characterization. So I quibble with disnissing it out of hand......Drakkith said:
Aye, the beauty of conspiracy theories is that the best conspiracies leave no evidence.renault said:
Perhaps I was overly harsh on the descriptions.hutchphd said:
You have mistaken "there's no good evidence for this" with "everything is fine, stop questioning, you're being stupid". I don't care whether or not you continue to look into a topic. But I also know that health and safety information about any topic is almost always distorted and misunderstood by virtually everyone not professionally experienced with that topic. If I were to follow every piece of advice on every health topic I can find online I'd never eat red meat, never eat sugar, never eat fats, undercook my food, overcook my food, eat raw food, eat zero processed foods, not watch TV or use a computer, take only 'natural' medicine, get acupuncture or use healing crystals or something, not get vaccinated, not use sunscreen, not get an MRI or an X-Ray, drink non-fluorinated water, drink ionized water, not live near power lines, not use wi-fi or cell phones, use blue-light blockers... should I go on?renault said:
in the interest of not boring others, I will simply say that I wish you well with taking your 'number 1' choices, personally I tend to take your number 2 option, being guided by the 'follow the money' principal and generally what I see around me. I will be happy to continue this line of discussion if you want to create another topic if you wish, but now I am gong to bring this thread back on the topic I started.Drakkith said:
Fair enough but that is zero to do with how Science works and this is a scientific forum. I would read the Forum mission statement again.renault said:
I am interested in your idea of putting bulbs in glass bowls. Just as an example, are you saying that if I put a jam jar over my bulb, the wavelengths of light emanating from the jam jar would change.?Vanadium 50 said: