Shopping & Style1 min ago
Daylight Bulbs
There are a number of 'biobulbs' available on websites claiming to give a light close to that of daylight, but none show an emission spectrum to substantiate that claim. Does anyone know if this information is available anywhere, or can shed any light on it ;-)
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This is a Canadian/US site; however, the information in it should also apply to the UK.
http://www.homedepot.com/webapp/catalog/servlet/ContentView?pn=KH_BG_EL_Choosing_CFL_Light_Bulbs&storeId=10051&langId=-1&catalogId=10053
http://www.homedepot.com/webapp/catalog/servlet/ContentView?pn=KH_BG_EL_Choosing_CFL_Light_Bulbs&storeId=10051&langId=-1&catalogId=10053
contains this:
What’s the difference between “daylight” and ordinary light bulbs?
There are several different types of daylight simulation light bulbs but one thing that they all have in common is that they appear far “whiter” than ordinary light bulbs. Ordinary (incandescent) light bulbs give off a very yellow light and although your eyes easily become accustomed to this, you do not see colours in the same way as you do in natural daylight.
If you compare photographs taken indoors when lit by normal incandescent light bulbs (without flash) with similar photographs taken in natural daylight you will instantly see the “yellowness” of normal light bulbs.
What is meant by “colour temperature”?
The colour of a light bulb is measured using a scale known as “Kelvin” (°K). Lower colour temperatures contain more red light and appear “warmer” whereas higher colour temperatures contain more blue light and appear “cooler”. Standard light bulbs typically have a fairly yellow light with a colour temperature around 2700°K whereas daylight bulbs give off a much “bluer” light at the same colour temperature of natural daylight - around 6000 to 6500°K. (also see our colour temperature page)
What does “CRI” mean?
Natural daylight is not just a single colour but, as we all know, contains all of the colours of the rainbow. It is this range of colours that enables our eyes to see in a way that we perceive to be natural and balanced. Light bulbs that give a good balance of colours and allow colours to be reproduced accurately are said to have good “colour rendering”. The colour rendering index (Ra) is measured on a scale of 1 to 100. Light with just a single colour has an Ra of 1 whereas that of natural sunlight is 100.
To see the effect of this, try looking at the cars in a street that is lit solely by the very yellow light of sodium streetlights – effectively a single colour of light. Although there is plenty of light to see the cars, deciding what colour they are is often extremely difficult.
What’s the difference between “daylight” and ordinary light bulbs?
There are several different types of daylight simulation light bulbs but one thing that they all have in common is that they appear far “whiter” than ordinary light bulbs. Ordinary (incandescent) light bulbs give off a very yellow light and although your eyes easily become accustomed to this, you do not see colours in the same way as you do in natural daylight.
If you compare photographs taken indoors when lit by normal incandescent light bulbs (without flash) with similar photographs taken in natural daylight you will instantly see the “yellowness” of normal light bulbs.
What is meant by “colour temperature”?
The colour of a light bulb is measured using a scale known as “Kelvin” (°K). Lower colour temperatures contain more red light and appear “warmer” whereas higher colour temperatures contain more blue light and appear “cooler”. Standard light bulbs typically have a fairly yellow light with a colour temperature around 2700°K whereas daylight bulbs give off a much “bluer” light at the same colour temperature of natural daylight - around 6000 to 6500°K. (also see our colour temperature page)
What does “CRI” mean?
Natural daylight is not just a single colour but, as we all know, contains all of the colours of the rainbow. It is this range of colours that enables our eyes to see in a way that we perceive to be natural and balanced. Light bulbs that give a good balance of colours and allow colours to be reproduced accurately are said to have good “colour rendering”. The colour rendering index (Ra) is measured on a scale of 1 to 100. Light with just a single colour has an Ra of 1 whereas that of natural sunlight is 100.
To see the effect of this, try looking at the cars in a street that is lit solely by the very yellow light of sodium streetlights – effectively a single colour of light. Although there is plenty of light to see the cars, deciding what colour they are is often extremely difficult.
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