Compact Fluorescent, LED, Halogen, Watt, Lumen, Candela… Explanations
1 – New Technologies Have Emerged
New sources of light have appeared on the market, at the expense of readability for the consumer. Before, the purchase of a light bulb was a simple act: we buy a bulb of a certain power, for a given lighting: 100W for good light, 25 or 40W for a smaller lamp, no issues other than the type of nerve (in small or large, screw bayonet).
The situation has become more complicated as a result of 3 factors of Shoppingpicks:
- New technologies such as LED or compact fluorescent bulbs
- New regulations prohibiting the use of traditional incandescent bulbs;
- Confusion of the institutional discourse (regulator and manufacturers) on regulation and new types of bulbs.
Should what key points we learn?
- Incandescent bulbs are actually removed from the market, except some very low-power models which do not concern this presentation;
- They are very advantageously replaced by 230V halogen bulbs that can be used in place and place, on same fixtures, offering a saving of around 20%. These bulbs produce a similar light, and are also compatible with dimmers to light with your installation or your luminaire can be already fitted;
- Fluo-compact technology undeniably offers substantial energy savings, but these bulbs produce unsightly “neon” light, are expensive to buy, and polluting: they contain mercury and, as a mobile phone, to produce electromagnetic fields that the effect on health is still being evaluated.
- The LED are definitely a solution for the future, but still suffer from technical limitations: fixtures designed specifically for LED, if they are well built, work perfectly, but can be used in place of traditional bulbs LED bulbs are clearly not convincing so far: high price and insufficient brightness.
In addition, the guide below will explain:
- How to measure the energy efficiency of a light bulb;
- Would you also be interested in the performance of its luminaries;
- What mean technical terms that appear in description of fixtures and recent bulbs: candela, lumen, lux.
2 – Light Output and Energy Efficiency of the Bulb
A bulb is like a transformer of energy: it consumes electrical power – found on its electricity bill – and in turn a part in light. This transformation is not perfect, a significant proportion of energy consumed is converted into heat. Each technology (fluo-compact, traditional incandescent, halogen, incandescent, halogen, LED) displays a different performance. In addition, two bulbs of same technology can reach different yields, including function of the quality of their construction.
The amount of light produced by a light bulb is measured in lumens. More a bulb is effective, more lumens for a given consumed electric power it produces.
The efficiency of a light bulb measures its ability to transform electrical energy into light energy. It is measured in lumens produced by watts of electrical power consumed. This is a similar approach to, for example, measure the consumption of a car in litres per 100 km: how far can I travel with a certain amount of fuel.
The table below shows the electric power consumed, the amount of light and the light output for some examples of light bulbs.
We see that the best returns are obtained by neon tubes – that is why they are massively used in industrial or office – and lighting by fluorescent compact bulbs – which are just miniature neon. With returns of 50 to 60 lumens / W, these light sources consume 4 to 5 times less current than conventional incandescent bulbs.
Best current LED models also display high light output – and the fast progress made by manufacturers allow to plan medium-term levels well above still. In ideological, the LED available today remain modest power – they produce a quantity of light – from 100 to 150 lumens – much less than a small bulb of 60W, for example. For this luminaire manufacturers integrate sometimes several LEDs in the same light – but the limit becomes particularly economic, the LED still a high price.
Halogen bulbs offer a return of the order of 18 lumens / W – a saving of 20% to 40% compared to traditional bulbs.
3 – Performance of a Luminaire
The speech of our benevolent authorities focus on the energy efficiency of the bulb. But the amount of light produced is also depends on the performance of the luminaire which is equipped with.
The return of a luminaire depends on two factors:
- Features electrical and optical light source used (for example, bulb incandescent or set of LEDs);
- The ability of the luminaire to transmit this light around him: a simple surrounded by an opaque black shade table lamp has a lower efficiency to an identical lamp surrounded by a Lampshade white semi transparent. The problem for a designer is to produce a light fixture that is effective from the point of view of the return of the light produced by the bulb, while being decorative and comply with applicable safety standards. Where’s the lost by the luminaire light? She is transformed into heat, thus contributing to heating the House with the same efficiency as an electric heater.
In conclusion, lights in the greenest way possible requires to banish dark blinds luminaires and lighting preferably with bare bulbs.
4 – Illuminance – Measured in Lux
What we see with our eyes, it’s surfaces and objects that surround us – and to be enlightened. Illuminance measures the amount of light which illuminates. The degree of illumination is expressed in lux. It is easily measured with a light meter (it’s being used by professional photographers to check the good illumination of the subject – also known as the “cell”).
The table below shows several lighting levels as an example:
What is the relationship between the luminous flux (measured in lumens) and irradiance (measured in lux)?
Imagine a room empty and square of 3 meters with a ceiling at 3 meters from the ground. We hang a light bulb that generates a stream of 2000 lumens (for example, a light bulb halogen 100W without shade). The total area of the surfaces of the room (walls, ceiling, floor) is 6 x 3 x 3 = 54 square meters.
The average illuminance of the room is 2000 lumen divided by 54 square meters = 37 lux.
In reality, the lighting specialists commonly practice the reverse calculation:
- Based on the objectives of use and successful aesthetic imperatives, they choose the lighting level to reach, expressed in lux;
- Depending on the size of the surface to illuminate, they determine the flow of light total (expressed in lumens) necessary to achieve the level of illumination used;
- A set of fixtures is then selected, capable of producing the necessary total flow. Of course, other constraints are taken into account, including for a breakdown of aesthetic and ergonomic light. This is to take into account the way in which each luminaire distributes the light it produces – in space it’s approach to the next paragraph.
5 – Brightness – Expressed in Candelas
A bare bulb (or candle) light in virtually all directions. But many fixtures concentrated most of the light they produce in a more or less narrow beam. In assimilating this beam to a cone, we often measure the width of the beam by an angle expressed in degrees. More this angle is low, of course, more the beam is narrow. If her team a spot in-ceiling to three meters in height, a halogen bulb:
- 6 degrees of beam produced on the ground a circle of thirty centimeters in diameter;
- 35-degree beam produces a circle of 1.90 meters in diameter.
Among other things, the below calculator to calculate the diameter of the illuminated surface, depending on the width of the beam and the distance of the luminaire.
Experts measure the light intensity produced by a light bulb or a spot in its ‘useful’ beam using another measurement unit, the candela.
- For a given flow (in lumens), more this flow is concentrated in a narrow beam, more this beam has a high (in candelas);
- Measures the light intensity (in candelas) so the amount of usable in the beam light produced by a light source.
This somewhat esoteric definition hides the simplicity of use of the greatness she described – which is a direct link between the illumination of a surface and its distance from the projector, and allows a practical dimensioning of fixtures. E illuminance in lux to a surface at a distance D to a C candela projector is just equal to: E = C / (D x D). Two examples:
- Illuminates a 1000 candelas projector placed at a distance of 10 metres from a surface at a rate of 1000 / (10 x 10) = 1000 / 100 = 10 lux;
- Illumination of 50 lux by a projector placed at 5 meters, to install a 50 x 5 x 5 = 1250 candlepower spotlight. Of course, there are also the projector has a sufficiently wide beam to illuminate the entire reporting surface since its distance.
The calculator below allows you to calculate the illuminance obtained with a given light, from his power, his light bulb technology, the width of the beam, and the distance to the illuminated surface. It calculates the diameter of this surface, the amount of light in lumens produced by the light, the light intensity of the beam in candlepower and obtained illumination.
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