What is light?
Light is reflection. To get a good light image you need a complete light reflection, which is generated by artificial light by phosphorus powders in a tube or by the amount of LEDs in a led light. Daylight consists of visible light, ultraviolet light and infrared light:
Sunlight consists of 5% of UV light, 50% of visible light and 45% of infrared light.
Not all UV light reaches us. The UVC is completely filtered through the ozone layer and the atmosphere and does not reach Earth. Only UVA and UVB are important to us, UVB causes our body to create vitamin D. This UV radiation is also in a good full-spectrum daylight lamp.
What is colour temperature?
The colour temperature indicates which light colour the lamp itself gives. This is indicated by the Kelvin value.
Colour 2700 kelvin is very "warm" yellow light and colour 6500 kelvin very "cold" white light. In Europe, the perfect daylight colour is 5500 Kelvin.
What is colour rendering?
Colour display is the ability of the artificial light to accurately display the colours of illuminated objects as compared to the colour reproduction of the daylight. Daylight is set to 100. The closer the value of the light source is near 100, the closer the display comes to natural daylight, so objects look more natural. This is expressed in CRI or RA value.
CRI / RA is a general indicator of how "natural" colours are reproduced when illuminated by a particular light source. Generally, a CRI of 70 and higher is required for most applications. The standard lamps are in the 70 or 80 range. A better quality lamp is in the 90 range, preferably as high as possible: 95 or 96.
Why uva and uvb in a daylight lamp?
The uva and uvb radiation is very important for a complete light image and has proven utility for the body to stay healthy. A lamp that gives a high CRI, right Kelvin value and Uva / uvb is called full-spectrum daylight lamp.
Why not sit for a daylight bulb for 20 minutes, but integrate into the living / work area?
To get or maintain a good energy level, the body needs daylight. Outside is daylight throughout the day. That's what our body needs. Therefore it is important to receive daylight throughout the day. If you only have daylight for 20 minutes before a daylight lamp, your body will receive that daylight. But when you turn off the lamp, the body is experiencing a "dusk" and will respond to it with extra fatigue. This gives you a peak and a drop in your energy level and that is not the purpose of artificial daylight. Therefore, throughout the day, artificial daylight is important and a solution to combat winter depression or fatigue.
Colour display of light.
The colour rendering index is achieved by most lightproducts producers by measuring 8 colors with moderate saturation (pastels). The CRI (Ra) is measured over the colours R1 to R8, as shown in the figure below. In the measurement, the important colour red (R9) is not included. In practice, this means that an light can have a relatively high CRI value (> 90), while the "strong" red colour (R9) is poorly represented. Red is an important and dominant colour that occurs in skin tones, clothes, food (meat, vegetables), medical world, etc. Red is therefore essential for the natural representation of colours. That's why it's just as important to get a light in the total range, then you know that the red colour is also represented.
Today there are several brands of daylight lamps on the market. As soon as one speaks about a daylight lamp, one usually speaks about a high colour temperature ≥ 5000 Kelvin. But there are not many brands that also indicate how much CRI / RA value they have and if they measure the full R1-R15 range.
A good daylight lamp needs a CRI / RA value of ≥ 90 or higher measured in the R1-R15 range. If this is not the case, the light becomes very bright but a little greenish or bluish. Only when the CRI / RA value is ≥ 90 and measured in the R1-R15 range, you see the real light from outside, inside: daylight.
To support this story we did 2 measurements ourselves: 1 with a Philips Master led tube and 1 with a True-Light tube. We used the Essence Lighting passport PRO.
The Philips LED tube 6500 Kelvin, we measured: 6189 Kelvin.
True-Light fullspectrum led tube 5500 kelvin, we measured 5502 kelvin.