GE G8.5 brochure UV and damage to sensitive materials, Information on luminaire design, Ballasts

UV and damage to sensitive materials

The wall of the bulb, which is produced with specially developed ‘UV Control’ material, absorbs potentially harmful high energy UV radiation emitted by the ceramic arc-tube.

The use of UV control material together with an optically neutral front glass cover allows the lamp to significantly reduce the risk of discolouration or fading of products. When illuminating light-sensitive materials or at high light levels, additional UV filtration is recommended. Luminaires should not be used if the front glass is broken or missing. It is recommended that a safety interlock switch is incorporated into the luminaire to prevent operation when the luminaire is opened.

Although PET determines limits of human exposure to lamp UV, the risk of fading of mechanise due to UV can be quantified by a Damage Factor and a Risk of Fading. The risk of fading is simply the numerical product of the illuminance, exposure time and damage factor due to the light source.

Finally the selection of luminaire materials should take into consideration the UV emission. Current UV reduction types on the market are optimised for UV safety of human eye and skin exposure. However, luminaire materials may have different wavelength dependent response functions. Designers must take account of emission in each of the UV-A, UV-B and UV-C spectral ranges as well as material temperatures when designing luminaires. Typical values for UV-A, UV-B and UV-C range radiation can be found in the table below.

		20W	35w	35w	70w	70w
Lamp type		3000K	3000K	4200K	3000K	4200K
UV-PET Performance µW / (cm²) / 500LUX
UV C	220-280nm	0.036	0.0367	0.020	0.014	0.011
UV B	280-315nm	0.049	0.0467	0.040	0.006	0.009
UV A	315-400nm	10.170	10.360	113.870	6.980	9.800
UVC/UVB		10.720	0.786	0.509	2.365	1.321
UVB/UVA		0.005	0.005	0.003	0.001	0.0099
Eeff		0.052		0.034	0.015	0.014
PET (h)±10%		16	15	26	54	64
Risk Group	IESNA RP-27.3-96	Exempt	Exempt	Exempt	Exempt	Exempt

Information on luminaire design

Ballasts

ConstantColor CMH™ operate from the same type of ballast as conventional quartz technology metal halide lamps of the same nominal power. IEC 61167 MH lamp standard and IEC62035 HID lamp safety standard specify use of ballast thermal protection or equivalent protection device in the circuit. This safety device will protect the ballast and fixture from overheating damage at lamp end-of-life should rectification occur due to electrode imbalance or arc-tube failure. The IEC61167 requirement applies to both ceramic and quartz arc tube metal halide lamps of the UV-A, UV-B and UV-C spectral ranges as well as material temperatures when designing luminaires.

ConstantColorTM CMH G8.5 lamps are compatible with a list of approved ballasts; contact your GE representative for more information.

Stay magnetic field from conventional ballast

At the design stage for fixtures incorporating the control gear, careful consideration should be given to the physical layout of the lamp and ballast. The relative positions and distance between lamp and ballast can adversely affect lamp performance and drastically reduce lamp life survival.

Conventional magnetic ballasts can produce a stray magnetic field and if the lamp is placed within this field, “bowing” of the arc in the discharge tube can occur. Since ceramic is a very rigid material severe arc bowing can cause high thermal stress leading to cracking or rupture of the arc-tube resulting in failure of the lamp early in life.

Such bowing of the arc can also affect the quartz arc-tube in conventional metal halide lamps, but cracking or rupture failure is less likely since quartz softens at the resulting higher wall temperature causing the arc-tube to become swollen. Excessive swelling of a quartz arc-tube can however also result in cracking or rupture failure.

In fixtures where the ballast is necessarily placed close to the lamp, use of magnetic shielding is essential. Another solution is to use an electronic ballast, which eliminates the need for an ignitor, simplifies wiring, reduces the risk of stray magnetic field and eliminates light output flicker.

Electronic ballast operation

CMH 20W is designed only for operation from electronic gear*. This provides many advantages:

•Flicker free light output

•Well controlled electronic ignition process

•Simple wiring for fixtures due to elimination of ignitor and

PFC capacitor

•Reduces fixture weight

•Automatic sensing of failed lamps and shutdown

•Lower overall system power consumption

•On further details of operating gear please refer to GE

Circuit diagram

electronic ballast

LH = Lamp holder

E = Electronic Gear

Mains

N P

E

LH

Containment requirement

ConstantColor CMH™ lamps operate above atmospheric pressure, therefore a very small risk exists that the lamp may shatter when the end-of-life is reached. Although this failure mode is unlikely, containment of shattered particles is required as prescribed by IEC 61167. ConstantColor CMH™ lamps should only be operated in a suitable enclosed luminaire with front cover glass capable of containing the fragments of a lamp, should it shatter.

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