Light article in Summer 2018 Challenge Magazine
Steve Bolter charts a revolution in lighting
When I started school in 1947 London, the classrooms had tall windows and coal-gas lights. Home had filament lamps.
My current home has Light Emitting Diodes. Even the National Trusts has embraced modern lighting technologies in its historic houses; but many ordinary households have not.
The paucity of quality information, and confidence shattering free samples of very dim "energy savers" are partly responsible for the reluctance to change.
The Victorians built my school for maximum use of daylight. Gas lights were only for dull winter afternoons. Modern buildings have low ceilings and are designed to fit the site, rather than to catch the sun, making it even more important to have efficient lighting.
Achieving efficiency does not just depend on the efficiency of the lamp. White ceilings, light walls and furnishings, unobstructed light paths, diffusing rather than absorbing light shades, conveniently positioned switches, and the design of light fittings contribute too.
Measuring light and colour
Light flows are measured in lumens. The unit is part of a system based on the stimulation the light produces in the normal human eye.
The luminous efficiency a light source is the ratio of the light flow produced, to the power the source consumes. The unit is the lumen per watt [ lm / W ] .
Colour temperature is used to express the whiteness of light.
All matter emits I R, visible and UV radiation. The predominant type and colour of the radiation depends on the temperature. The temperature at the surface of the sun is about 5000 kelvin (or 4727°C). A light that looks like sunlight has a colour temperature of 5000 kelvin (symbol K).
The tungsten filament in a traditional bulb operates at about 2700 K. Its light looks yellowish. Light that looks like light from a filament lamp has a colour temperature of 2700 K.
Filament lamps are very inefficient light sources. More of the power supplied to them is converted to invisible Infra-Red radiation, than to light. Modern alternative "white" light sources, give white light without wasting energy in generating IR. Lamps giving 2700 or 3000K "warm white" are recommended for relaxing by. 4000 K white or 5000 K daylight lamps are suggested for work spaces, kitchens and bathrooms. Because the visible spectra of such "white" lights are not exactly the same as those of sunlight, objects lit by them may not look quite the right colour. Various colour rendering scales have been designed. The closer the value is to 100, the better the colour rendering. (For a rigorous treatment of colour temperature visit the G L D website)
By making the filaments short and fat or long and thin, incandescent lamps can be made for direct connection either to low or high voltage supplies. Most other light sources require controllers to match to the supply voltage and control the current. LEDs require controlled Direct Current.
Some non-filament lamps have built-in controller, so that they can be plugged in just like filament lamps. Others are used with external control units. When assessing efficiency, one has to include the power used in the controller as well as the lamp itself.
When using fluorescent or LED lamps, any dimmers or electronic switches used have to be compatible with the controller electronics.
These are filled with mercury vapour. An alternating voltage causes electrons to crash into mercury atoms, which then release UV. That causes the phosphors on the inside of the tube to glow. The blend of phosphors determines the colour of the light.
Compact Fluorescent "energy saver" or "eco" lamps
These are folded miniaturised fluorescent tubes. They are generally less efficient than full size fluorescent tubes. They are slow to reach full brightness, and perform poorly in cold conditions sold off very cheaply as "energy savers", but shorter life and lower efficiency make them much more expensive overall than LEDs.
Light Emitting Diodes
LEDs save the most energy. They emit light when electrons move between two semiconductors. Different pairs of semiconductors produce different colours. A mix of red, green and blue LEDs can produce an approximation to white light. The useful life of such LEDs is over 30 000 hours, but their colour rendering is poor.
Modern "white" LEDs include phosphors. The actual LEDs produce mostly blue light, but lamps include phosphors which convert some of the blue into a yellowish broad spectrum of light. The phosphors are blended so that unconverted LED light, plus light from the phosphor, give white light.
LEDs with phosphors produce good colour rendering, but do not maintain their brightness for quite as long. They last over 10 times longer than filament lamps.
Since 2012, affordable domestic white LED lamps, with phosphors and internal control gear, giving good colour rendering, have been available with efficiencies of over 100 lm / W. Versions with a controller that can be used with a suitable dimmer are slightly more expensive.
Light from Colour LEDs can look different to that from white lights with filters. It is advisable to see the colours before purchase.
The LED is the best option for most domestic lighting, the main exceptions being inside ovens, and in beloved old fittings with electronic switching or dimming designed for fluorescents or filament lamps. (If they are not loved it would greener to replace them with ones for LEDs.
A common 13 watt GLS LED gives 1520 lumens, [almost equal to the 1600 lumens given out by a 100 W filament bulb] making its luminous efficiency 1520 lm /13 W = 117 lm/W.
With the tradition central "General Lighting Service" bulb suspended from the ceiling, light from the cap end is reflected back from the ceiling to soften shadows. LEDs are available in "GLS" bulb shapes, and in stick shapes that send little light little light towards the ceiling.
For LEDs with a diffusing white envelope, The amount of white visible from a particular direction gives a rough guide to the amount of light that goes in that direction.
Downlighters incorporate narrow angle LED floodlights or spotlights. They are fine for lighting the floor, but not much good for seeing faces in mirrors, or for uniformly illuminating work surfaces, unless on a high ceiling, or fitted in large numbers. (Good for fitters!).
An alternative for work surfaces is a strip of low power LEDs, sharing a single controller, mounted under a shelf or on the ceiling.
Kitchen up-light can be provided by an LED strip light on top of a cupboard, out of direct view. Tubes enclosing a strip of LEDs, that fit directly into old T8 (slim) fluorescent tube units, are available on the internet.
These tubes contain the LED control gear at one end. The old fluorescent tube control gear has to be disconnected, (but can be left in place) and the wiring adjusted to bring live and neutral to the two pins at the controller end of the tube.
Lamps and light fittings, or integral units.
Incandescent lamps are very hot, small intense sources of light, that have to be replaced every 1 to 2 thousand hours of use. They were mounted in light fittings (or 'lanterns') to isolate the heat and protect from glare.
LED lamps are cool, their light output can be spread over large areas and they last 15 to 30 thousand hours. Although often used in conventional fittings, LED lamps can be designed to be used directly on their own. Under shelf lighting and ceiling lights for kitchen and bathroom are often integral fittings.
Green Liberal Democrats advocate better package labelling, to facilitate and encourage change to lower energy lighting. Referring to newer light sources filament lamp equivalent power is confusing, and increasingly redundant as fewer changes will be directly from filament lamps. Terms such as 'ecolight' or 'energy saver' should be replaced by simple descriptions such as 'LED' or 'halogen' or 'compact fluorescent', as LEDs give more energy saving than earlier "energy savers".
Product packaging should show the light output (in lumens), the actual wattage, the colour temperature, the spread of the light, the cap type, and the supply voltage if relevant. The wattage and/or the lumen output should be clearly visible on the on the device itself
Websites and retailers should have charts for the typical lumen output of different types and powers of lamps.
Hints on LEDs
Beware of very cheap LEDs. Make sure they have a genuine CE mark, or whatever the Brexit replacement. LEDs are expensive and long lived. Get one or two to try out in various locations before bulk buying. If the lumens are not printed on the lamp itself, write them on as a guide for future purchases when the box is long gone. An LED saves even more when switched off!.
Steve Bolter is a member of the GLD executive
- Website only supplement which firstly explains some of the terminology and gives some science background for those who are curious. Then it moves on to wide issues. After Colour temperature will come something on the biological effects of artificial light. Download PDF
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