The World's Only
Flashlight Industry News Site

Are Xenon Burners Still
Useful Illuminators?

---

FlashlightNews.org - 12/6/2011 A -     A +

By Urs Baeumle -- Permalight (Asia) Co., Ltd.

Continued from Page 1

"Light Power" - Light Measurement Units

There are many and sometimes confusing light definitions and measurements units, such as Watt, Candela, Lumen, Lux, Luminescence, etc. some of which are explained below. For comparison, this paper focuses mainly on Lumen and Lux as both are understandable to and can easily be verified by laymen.

This comparison shall explain some technical and optical differences between the two but also illustrate advantages of Xenon burners and reason why they will remain useful for some time to come.

Lumen [lm] - is the total amount of visible light emitted by a light source in all directions. In simple terms, Lumen may also be described as 'outgoing' light. However, one must be aware that Lumen do not correspond with 'brightness' as perceived by the human eye!

Lux [lx] - is the light intensity hitting a surface at a distance and the resulting 'light coming into the human eye'.

Candela [cd] - Is the luminous intensity or amount of light (flux) emitted in specific direction by a light source. A common household candle emits light of an intensity of one Candela measured at the distance of 1 metre or 1 foot respectively.

Luminescence [cd/m2] - The intensity of the amount of light (flux) leaving a surface in any given direction measured in Candela per square metre (or square foot - cd/ft2)

Watt [W] - Measures the power energy measures and not the 'light output'! It indicates the energy consumption of the light device.

Colour Temperature [K] - Measurement of the colour of 'white', expressed in 'Kelvin'. Reddish light has a lower and bluish light has a higher colour temperature.

The table below compares Lumen and Lux of Pila® tactical and Parat® X-treme safety lights. Lux were measured with a calibrated Lux Metre at a defined distance of 1.5 metre.

	Lumen	Colour Temp.	Lux @ 1.5m
6V Xenon (Pila GL2)	120 Lumen	Around 3,000 K	8,500 Lux
9V Xenon (Pila GL3)	200 Lumen	Around 3,000 K	13,500 Lux
3.7V - 9V LED (Pila)	250 Lumen	Around 7,000+ K	2,600 Lux
1W Xenon (Parat PX 2)	10 Lumen	Around 2,500 K	330 Lux
0.5W LED (Parat PX 2)	20 Lumen	Around 6,000+ K	200 Lux

Notes:
• Pila® tactical and Parat® X-treme safety lights are manufactured by Permalight (Asia) Co., Ltd. www.pilatorch.com

• Parat® trademark is registered and owned by Parat Gmbh, Germany.

From the above table it is evident that higher Lumen ratings do not directly result in higher Lux readings. Optics and physics will explain why the 200 Lumen Xenon burner fares better than the 250 Lumen LED emitter. One of the reasons is the size and form of the actual light emitter. Xenon bulbs include a round filament emitting light in all direction, which is then collected, reflected and emitted by the reflector. The LED is a miniature square dice emitting light in an angular direction. The LED light is focused with the help of a reflector or a collimator. As previously explained, the quality of reflectors respectively collimators are essential for reaching optimal luminance. The main factor to achieve higher Lux readings is that the Xenon burner has a higher Watt rating and so more 'light power' than the LED emitter.

When correlating 'light power' with 'distance' or 'light throw', one must remember that Lux values decrease by inverse square (1/x²) to the distance between the light source and the illuminated surface because the amount of light will be spread on a wider area. Therefore, the longer the distance, the 'dimmer' the light is perceived by a standard observer. Consequently, Lux ratings of different luminaries must be measured at defined distances.

'Light power' versus 'light efficiency' - in our example, the Watt rating of the 9V Xenon burner (200 Lumen) is around 9 Watt and has, therefore, more 'power' than the 250 Lumen LED 3 Watt emitter. But as most of the generated 'power' is lost as heat, the efficiency rate of Xenon burner is reduced to 22 Lumen/Watt compared to 82 Lumen/Watt of the LED emitter!

"Light Throw" Compared to Detection, Recognition and Identification (DRI)

'Light throw' is an subjective distance assessment depending primarily on the observer's eyesight and on prevailing environmental factors, such as humidity, rain, fog, temperature but also on the degree of darkness - moonlight, starlight, overcast sky.

The paramount question is: What can I see at what distance under what conditions?

It is easier for everyone to visualize a beam 'illuminating a path of 100 metres' than imaging an absolute value of 0.85 Lux, the amount of light captured by the eyes.

To truly assess and compare the performance of different luminaries, 'Detection, Recognition and Identification' (DRI) of objects at different distances should be taken into consideration. DRI is a terminology, also referred to as 'Johnson Criteria', predicting the performance of electro-optical sensor systems under different environmental conditions enabling observers to detect, recognize and identify objects of defined sizes at set ranges.

Detection - barely see 'something'
Recognition - discern a car versus a person
Identification - determine the car model, distinguish a woman from a man

Like electro-optical detectors, the observer's eyes are the human visual sensors designed for scanning surroundings and to detect, recognize and identify different objects. It is apparent that environmental conditions such humidity, temperature, degree of darkness (moon-, starlight, overcast sky) but foremost fog, rain and snow will affect and reduce the "Light Throw" of luminaries greatly. In heavy fog or pouring rain, instead of being able to recognize an object or a person at 100 metres, the same observer will barely be able to detect the target at 20 metres, not to mention the blinding reflection effect of high-power lights.

The below pictures show and compare the 'light throw' of 6V respectively 9V Xenon burners and LED emitters as well as two low Lumen LED and Xenon penlights.

The 12V Xenon 550 Lumen illuminator serves as reference showing the lit-up area for better orientation. Of main interest were distances at which different objects and colours could be recognised and distinguished by the observer respectively captured by the digital camera; e.g. the white (foreground) and black vehicle (middle) and the orange truck at the far end. Readers must be aware that the spectral response of the human eye with its well over 120 million light sensors (rods and cones) is far more light and colour sensitive than a 8.7 Mio. pixels (8.7 Mega Pixel) digital camera CCD sensor. In the test setup, the orange truck illuminated with 9V Xenon (200 Lumen) appeared to the observer's eyes as 'orange' and under LED light (250 Lumen) as brownish. Yet, under LED light (250 Lumen) the CCD camera sensor captured, with delayed shutter active, the scene to appear much 'brighter' than if flooded with Xenon 200 Lumen, a phenomenon which can partly be attributed to the 'white' sensitivity of the CCD sensor and optics and partly to the narrower LED light beam.

Test conditions:

• Distance to white car : around 50 m
• Distance to orange truck : around 130 m
• Temperature : 30°C
• Humidity : 78%
• Ambient light : present in background, half-moon
• Sky : Slightly overcast
• Visibility : 10 km

Reference Picture
12V Xenon 550 Lumen
Shutter 8 & F2.8

6V Xenon - 120 Lumen
Shutter 8 & F2.8

9V Xenon - 200 Lumen
Shutter 8 & F2.8

3W LED - 40 Lumen
Shutter 8 & F2.8
(Note: Pila 'Quick-Switch' LED Emitter at 15% light output)

3W LED - 250 Lumen
Shutter 8 & F2.8
(Note: Pila 'Quick-Switch' LED Emitter at 100% light output - Camera CCD responds to white LED better than to Xenon!)

Penlight - 10 Lumen
Shutter 8 & F2.8

Penlight - 0.5W LED 20 Lumen
(Note the 'bluish' shift of the white car.)

Reliability (Meantime Between Failure)

The 'light source' in a Xenon bulb is a very thin tungsten filament which will burn and break over time. The tungsten filament is encapsulated in a glass enclosure filled with highpressure Xenon gas, the actual light medium. Manufacturers of miniature quality Xenon burners state the Meantime Between Failure (MTBF) to be around 25 hours despite some bulbs might last for 100 hours or even longer. LED chips are declared to function for 100,000 hours but such statements are only partly correct. LED chips per se have indeed a very long lifespan but the LED modules' failure rate depend on a number of electronic components, some having a life span limited to a few thousand hours only! Therefore, the MTBF of LED modules depend solely on the weakest electronic component and solder points reducing the "guaranteed" LED MTBF greatly! Cheaper LED flashlights often drive the LED directly from the batteries without using any safety circuit or driver. In this case, LEDs are easily 'overdriven' and become overheated with the result that they will turn blue and fail within a few thousand hours of operation. Yet, it is clear that, under normal conditions, LED emitters will outlive Xenon burners!

Conclusion

The presented comparison between Xenon burners and LED emitters demonstrate that Xenon have still some optical advantages over LED lights, which are: 'Light power', better colour rendition and contrast results. These properties are favoured by numerous individual operators and might be considered as important by specialist personnel, mainly in law enforcement, military and in the engineering field. For these reasons, Xenon burners will retain their operational values for some time to come. However, the above observations and explanations make it apparent that modular flashlights which allow the free interchange of Xenon assemblies and LED emitters present the best light options and optimal operational choice!