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575 Watt Loads

Bulletin Number: 149
Released By: Don Stauffer
Product Family: ULD 360 DIMMER
Date: 8/26/2004
Classification: Advisory

The 575 watt lamp as used in the Source 4 and other popular fixtures has become very common in the industry. As a dimmer manufacturer, we have become aware of some issues with these lamps over the past few years.

The lamps are available from several well-known manufacturers. Some offer 115 and 120 volt versions of the lamps. If the fixtures are used in venues with line voltage over 115 volts, it is important to use the 120 volt lamps.

If the lamps are used at higher than rated voltage, it can cause shorter lamp life and present a larger load to the dimmer circuit. Instead of presenting a 5 amp draw, the lamps will require 5.5 amps or more.

Even at rated voltage, it is not uncommon for these lamps to draw more than the stated current. Here is the actual measured current for six new lamps randomly purchased from local suppliers. Note that ALL lamps tested draw more than 5 amps:

Sample Manufactuer Current draw Watts
1 Usihio 5.16 593.4
2 Philips 5.24 602.6
3 Osram 5.09 585.4
4 Ushio 5.13 590.0
5 GE 5.13 590.0
6 Ushio 5.33 613.0

The ETL Listed version of the ULD dimmer uses a NEMA 5-15 plug for convenient connection to standard electrical outlet. Along with that 15 amp cord set, we are required to use a 15 amp breaker. There are cases where three lamps will draw over 15 amps, and trip the circuit breaker.

We recommend using 120V lamps whenever possible to keep the load within spec. Several lamp manufacturers offer 'Extended Life' versions of the 575 lamp, these are a good choice for dimmers that are loaded to 100% of the dimmer rating.

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