Thanks MYN. So it is reasonable to say that the light of a pressure kerosene lamp is about the same or similar to an incandescence lamp? Electric incandescence lamps are about 2400 K to 2700 K according to wikipedia. So if you say that mantle~blackbody@2000-2500K, then they are about the same. True? But why do you say that the CRI is not the same? About health issues of the light: Checking the black body article of Wikipedia the first graph shows that at 5000K converts part of its energy to UV which is considered dangerous. When you reach 3000K there is almost no UV. Going lower to a classic pressure lamp things get even better. Candles are at 1700 K and they also have 100% CRI. So, is it correct to assume that the light from classic pressure lamp is "healthier" in this sense? (forget about other problems with the kerosene). I try to understand where the light of classic pressure lamps stands for health and color quality in the series from the candle to the today's widely used leds. For example, being more red than blue should be better for the circadian rhythm and should not badly affect sleep as leds do. I do not know what happens in other countries but suddenly the TV in Greece has been bombarding us with melatonin products for better sleep. I started from this observation to investigate what is going on with old and new light sources.
Well I did mentioned that they're not exactly the same in a sense that the similar wavelength ranges were not being produced with exactly the same physics. Despite that, I'd reckon that they usually do have similar CRIs..(both the light emitted from the incandescent electric lamps and the classic gas mantles). Similarly, the modern LED-type of light source could be made to produce similar CRI as the electric incandescent light sources, daylight/Sunlight or almost any desired colour temperature without the need to make things that hot. As you would know it, the LED could be made to emit more light with frequencies towards the blue or ultraviolet ranges. It would have required a solid to be heated to temperatures in excess of 6000K(without melting or vaporizing off) in order to produce it. Practically impossible. No known material on Earth could remain solid at those temperatures(I mean without subjecting it to extremely high pressures). Those are in the realm of electric arcs and plasmas which, are not considered blackbody radiation simply because they were not emitted from heated solids. The light flash created from a nuclear detonation is another matter.
There are some exceptions somehow. Ok, for example, if tungsten or rhenium are being heated to just below their boiling points, you might get quite close to the blue range. Light radiation from molten material might still be considered blackbody radiation since plasmas are not involved yet.
There are health issues related to light and information is scattered throughout the Internet. It is not easy to understand what is going on unless you are an expert (in the science sense). So Colin indeed CPL is very useful. Now, about leds. I understand that they can be made to mimic incandescence. However, they are not! V-tac for example produces leds for home lightning at about 82 CRI. Most leds for home use are about 80% (wikipedia). Very few companies sell leds above 90% and are not sold in most countries. I found 1 company that produces leds at 99% available only in US. Philips does produce hi CRI leds but their external design is ugly. Home leds in Greece are often in a candle_flame_shape and these are 80% typically. So this comes down to the fact that most people have to live with 80% CRI and lamps that the only information given on them is temperature in Kelvin. Many bars here, trying to make their customers feel good and objects with true color (such as the label of a bottle) refuse to go to leds. They still use incandescent electric lamps even if they have to look for them in the "black market" (they are forbidden in EU). So 80% gives more blue than red. More cataract for our eyes (experiments with rats are clear about this), less melatonin, less quality sleep. So I think that companies must be forced by law to write CRI on their products as well as emissions on the UV range for the high temperatures. Ozone protects us from the Sun UV but manufacturers with their 5000K brought UV in our life without ozone protection. True or false? So what is the proper advice for people? 1st Buy a classic pressure lamp (*) 2nd Prefer incandescence electric lamps until the led companies decide to behave humanely Of course we have to deal with the environment which is in danger. I wonder though.... led lamps are all plastic. Are they really so good for the environment? What is needed to produce them? (*) although I do not understand this market. All companies that sell CPL say "out of stock". All (except one in US for only one model). But if you talk to them they will find one for you. So why they are "out of stock"? Who knows...
Well the bar can still choose to use classic mantle lamps. Incandescent electric lamps are getting scarce these days except for automotive headlights and some applications requiring tungsten/quartz-halogen ones. These are usually rated around 3000K colour temperature. I think its a little more costly to make LEDs with 100 CRI. That is partly due to difficulties and additional measures to obtain the right blend of wavelengths at the ideal relative output amplitudes with respect to each colour. There are of course other methods of measurements that could dispute the CRI measurement but that would be way off topic. Not everything has to produce colour temperatures close to that of Sunlight on order to have 100 CRI. That would introduce too much blues, violets and UV. Other than incandescent lamps, there are other electric light sources(besides LEDs) than can produce the colour rendering close to or at 100. These include certain 'short-arc' xenon discharge lamps and similar devices. However, these are not conveniently applicable for general domestic use. They are more for larger scaled applications such as special lighting for live video broadcasts, some studios and other spectrally demanding applications. Needless to say, the setups are costly. They consume substantial amounts of energy too. They are not incandescent lamps. As for here in where I live, the plain old general purpose incandescent bulbs are still available on the market but have greatly reduced in quantity.
Just to be noted, so it stays in CPL forum, it seems that leds take advantage of the "metamerism" effect not producing a full spectrum (as Sun, incandescence lamps and cpl mantles). You can produce "white" by blending all colors in equal amounts or by blending specific colors in certain amounts. The human eye will see the same color of the produced light: "white", because it contains three type of cells that get excited around peak values of blue, green and red with sensitivities around these peaks that overlap with each other. But the accuracy of the color objects reflect, will depend on the mixture of the light they receive. As a consequence humans may say that these two lights are both white but when the same object is brought under these lights they look as having different colors. So what MYN says makes full sense. It is much more difficult to make a led lamp produce 100% CRI of the incandescence or approximate the CPL mantle. Finally wikipedia says that many leds contain lead and arsenic. If true, then they are energy efficient but they are not the "environmental angels".
Seems that what we see is not always what we get. They will just produce what most people would roughly perceive as 'white' on first sight....until they notice the colour differences being reflected off objects later at home . As we get older, our eyes become less adaptive to subtle changes to spectral differences. We tend to require higher CRI in order to read or see normally. I could no longer see as well in the dark as I used to and took longer to determine the correct colours of objects under less than ideal CRI lighting.
Do you know if a 99% CRI led lamp is n ecessarily less efficient in energy consumption than an 80% one?
It could be. Energy efficiency or efficacy for these stuffs are usually rated with units of lumens/Watt (lm/W). Electrical light sources(LED gor instance) to produce the right amount of the selected wavelengths might not be as energy efficient as those having different colour outputs. Lumen output has nothing to do with the colours. To get the right blend of colours, some efficiency could also be compromized.
