More About Lamps

This information is intended as a general background guide to tungsten halogen filament lamps, the principal light sources for theatre lighting.

Filament lamps generate light from the heating of a tungsten filament wire to white hot. The management of this heat is a major consideration in luminaire design. Be aware of the fragile nature of these lamps when operating!


Always refer the manufacturer’s instructions regarding handling and disposal of failed lamps. Use the plastic glove or packaging to mount the lamp in the luminaire to ensure no harmful skin oils are transferred to the quartz lamp envelope.

Lamp Life

Lamp specifications refer to ‘Average Lamp Life Hours’ This refers to the number of hours when 50% of the test batch size remain operating - 50% have failed, 50% are operating satisfactorily.

These tests are carried out in the manufacturers' labs in open air, i.e. not in your luminaire. Luminaire design is therefore key to achieving average life hours.

Lamp life is a compromise between output and performance. High output lamps such as CP and P – studio lamps have a short average life, 50–200hrs; typical theatre lamps T class etc 300–900hrs and long life lamps 1500–2000hrs. Output varies accordingly with a drop in colour temperature and rendering from the highest performance, short life lamps (3300–3200K) down to the 2700–2900K for the long life lamps.


Effect of Under/Over Voltage on Lamp Life

Note the halogen cycle is affected by the lamp temperature. The lamp envelope should operate between  250°C and 900°C to maintain effective operation of  the halogen cycle.

Operating the lamp at below design voltage will increase lamp life. A 5% reduction will increase lamp life by 200%.

Conversely operating the lamp over the design voltage will dramatically decrease lamp life e.g. 5% over voltage will halve the lamp life.



Fig. 1 (left)

Typical Life Variation Against Operating Voltage

Calculations of lamp life achievement taken from this graph should be considered strictly theoretical as the life factor is considerably influenced by frequency of switching, environment, vibration, handling, cleaning etc. This graph is based on the average achievement of numerous lamp tests, and thus should only be used as an approximate guide to performance.

Vertical axis = % Rated Life

Horizontal axis = % Rated Volts

Pinch Temperature

The pinch is where the quartz envelope enters and is cemented into the ceramic base. Temperature limits here are critical to ensure this joint is not heat stressed. Typical maximum pinch temperature for theatre lamps is 350–500°C, managing this temperature is a major requirement in luminaire  design.

Colour Temperature

The colour of the light source compared to a heated black body radiator measured in degrees Kelvin (K).

Colour Rendering (Ra)

The colour of the light source based on the appearance of various colours compared to that using a reference tungsten halogen source of 100 Ra.

LCL – Light Centre Length

Typically the height from the bottom of the ceramic mount to the centre of the filament. Centre reference point for the optical system of  Fresnels and PCs - reflector/centre of lamp filament/centre of the lens.

Important Maintenance Note

Lamp socket contacts will deteriorate over time. This process will accelerate if the contact terminals are not kept clean. As soon as signs of over heating (scorch marks) pitting etc are detected on either the lamp terminals or in the socket replace it!

Poor contact will increase the resistance leading to over heating and the possibility of critical cable failure and equipment short circuit.

Lamp Sockets used in Selecon Luminaires




Medium Bi Pin:

Acclaim Axial

Pacific 575W, 600W, 750W, 800W




GY 9.5:

Acclaim Fresnel, PC

Pacific 1000W




GX 9.5:

Rama 150 and 175 Fresnel

Rama 150 and 175 PC





Rama 6” and 7” Fresnel

Rama 6” and 7” PC




Rama 150 and 175 Fresnel G22

Rama 150 and 175 PC G22

Arena Theatre Fresnel & PC

Arena Zoomspots

Pacific 80V lamp module

Pacific MSR 575 HR lamp module




GY 16:

Arena Theatre Fresnel & PC

Arena Zoomspots




G 38:

Arena Fresnel & PC – North America models






Hui, Lui and Aurora ranges of Cyc, Flood and Groundrow



*R7 lamp sockets for double ended linear halogen lamps. Secure mounting of these lamps into the sockets is essential to avoid premature failure of both the lamp and socket. Use of high quality lamps from reputable manufacturers is recommended to minimise the risk of out of tolerance lamps.