Lighting is one of the most important features in the workroom when painting repairs on ceramic bodies. Without the right
colour and intensity of light, it is difficult to achieve colours that match and that will remain true under other light sources.
Often our ability to match colours can be traced back to the lighting being used, either the customers or ours. To understand
this you have to know a little about light and how to measure it.
Visible light is considered that portion of the electromagnetic spectrum that is used by our eyes to see. If the energy from a
light source is balanced in all wavelengths, the colour seen by the eye should be white. When another colour is seen, there is an
imbalance in the wavelengths of energy reaching the eye. Unfortunately, our eyes aren't uniformly sensitive, we see more red-
yellow-green in bright light and blue-green in low light.
There is more than one way of measuring light.
1. Brightness, the amount of light available is measured in lumens
2. Intensity The amount of light falling on a given area in lux or foot-candles.
3. Colour temperature (chromacity) is a measure in degrees Kelvin of the colour of the source of the light.
4. The radiant power that is emitted by a light at each wavelength is measured by the spectral power distribution curve.
5. The effect of a light's source on an object's colour is measured by the Colour rendering index, CRI
The amount of light available in your workroom should be enough to give 100 - 200 foot candles and up to 500 foot candles
on the work area where fine detail must be accomplished. Be sure that the lights are arranged to eliminate all shadows in the
work area as well. Once you have determined the number of lights needed, you can determine the colour of light. This will often determine the type of lighting you should have.
The chromacity will tell you the colour of the light. The lower the lights temperature the redder the colour and the higher the
lights temperature the bluer the colour. The output spectrum of incandescent light, halogen or regular is biased heavily toward
the red. Non halogen bulbs have a colour temperature of 2700 Kelvin , while halogen bulbs have a colour temperature of 3000
Kelvin - they are a slightly more whitish light. Regular fluorescent bulbs produce light in shorter wavelengths above 4000
Kelvin, usually in the orange/yellow portion of the spectrum, leaving out the red/blue/violet, however, they still do not produce a
full spectrum of colours. Some bulbs do add a blue tint, which gives a much truer colour rendering Chromaticity does not tell us
how well the light source renders colours, it just tells us the apparent colour of the source.
Light sources emit energy in selected wave bands, The spectral power distribution curve measures the light emitted by a source
at each wavelength in the visible region. White lights or full spectrum lights generally emit energy in all visible wavelengths.
Some white light sources especially the tri-phosphor bulbs can be deficient at some wavelengths. This affects colour perception
with some colours becoming greyer or brighter depending on the missing wavelengths. Full spectrum light may be new to many
people, but it is not a new concept. Full spectrum light simulates the full spectral power distribution of natural outdoor light.
Our eyes evolved in full spectrum light. It is the light in which we see best. The advantages of full spectrum light include
perceiving fine details clearer; performing visually demanding tasks (such as colour matching) more effectively; reducing glare,
thereby lessening eye fatigue and strain. Beware of the bulbs that advertise a large portion of ultraviolet light as ultraviolet light
bleaches out colours and may adversely affect (fade) items remaining under it for long periods of time.
Two bulbs that burn in the same temperature range can produce different colours! This is especially true in fluorescent bulbs.
The Colour Rendering Index, or CRI, of a source indicates how well it renders eight standard colours compared to a perfect
reference lamp of the same colour temperature. The comparison is only valid for lamps of the same colour temperature
(chromacity). The CRI index ranges from 1 to 100. A lamp with a CRI of 80 will render colours better than a lamp with a
CRI of 50. However, the CRI alone does not indicate colour accuracy. To compare the colour rendering capability of two
light sources, first choose two sources with an appropriate colour temperature for the situation. Then compare the CRI of
each source. The higher CRI source will render the colours in the space more accurately. Light sources having a CRI of 100
mean objects illuminated by it look like they are supposed to, their natural colour is not distorted. A light source having
a very low CRI would tend to make objects appear to be a different shade or colour than they really are.
Legislation went into effect Nov. 1,1997 in the US requiring light bulb manufacturers to produce fluorescent and some common
residential reflector incandescent bulbs that meet minimum federal efficiency and/or CRI requirements.
As you can see, the simple act of finding lights for your workplace can get complicated. A good lighting establishment should
be able to help you. So check the lighting in your workroom. For the best results it should be 200+ foot candles on the
workbenches with no shadows, full spectrum or at least tri-phosphor, and have the highest CRI index you can find (at
least 91). With this arrangement colour matching should be a snap.