Appendix DBulk lamp replacement interval for HPS Lamps#
Data available from lamp manufacturer Osram for their 250 w and 400 w high pressure sodium tubular lamps show the following lamp survival rates and lamp depreciation factors:
| Months burning | Survival rate (%) | Luminous flux (%) |
|---|---|---|
| 18 | 98 | 94 |
| 24 | 97 | 92 |
| 36 | 92 | 89 |
| 48 | 81 | 84 |
AS/NZS 1158 Lighting for Roads and Public Spaces specifies service availability of 95%. Using the manufacturer’s survival rate data, approximately 92% of the lamps will still be burning after three years. The failure rate increases rapidly after that time. A spot replacement program will assist in achieving the 95% level.
Maintenance factors (MF) used in lighting design are the product of the luminaire maintenance factor (LMF) and the lamp lumens maintenance factor (LLMF). Luminaire maintenance factors for IP5X and IP6X rated luminaires are found in AS 1158.1.1 Lighting for Roads and Public Spaces – Vehicular Traffic (Category V) Lighting – Performance and Design Requirements. Rexel Optispan luminaires installed before February 2002 are rated at IP54. Luminaires installed after this date are rated at IP66.
The following table provides the maintenance factors for various lamps, IP rating and pollution category for a 36 month cleaning interval based on the Rexel and Osram data:
| IP5X Low | IP5X Med | IP5X High | IP6X Low | IP6X Med | IP6X High | |
|---|---|---|---|---|---|---|
| 250/400W LMF | 0.88 | 0.82 | 0.76 | 0.90 | 0.87 | 0.83 |
| LLMF | 0.89 | 0.89 | 0.89 | 0.89 | 0.89 | 0.89 |
| MF | 0.78 | 0.73 | 0.68 | 0.80 | 0.77 | 0.74 |
Maximum allowable maintenance factors for IP5X luminaires is 0.7 and IP6X luminaires is 0.8. Having bulk lamp changes every three years with a minimal spot replacement program will enable the service availability compliance to be achieved as well as optimising road lighting design.