When prismatic and opal diffusers were very popular in the eighties and early nineties, we were all aware when regulations demanded that we use only TPa material in recessed luminaires - that is, a material that passes the 850°C hot wire test. This enabled the integrity of the ceiling to be maintained in the event of fire.

With the introduction CIBSE's guides of CAT 1, 2 and 3 there was a major swing to reflectors and plastic diffusers popularity waned.

With a more open view of workplace lighting and LG7, there is a new impetus to the use of diffused light or mellow lighting - and with this has come the increased use of plastics.

It is surprising how many specifiers have forgotten the requirement to use TPa 850°C material in recessed fittings - or maybe these specifiers were not in the profession 15 years ago.

Many lighting manufacturers are not making the consultant engineers aware of the regulations and subsequent breach of Part B of the building regulations by using TPb materials such as PMMA Acrylics, and the consequences of failure to comply with these.

Polycarbonate diffusers are required for TPa compliance, but these cause a loss of transmission that reduces light output ratios by around 7%. This then compromises many manufacturers ability to meet Part L energy efficiency of 45 luminaire lumens per circuit watt.

Anyone wanting to know the full requirements of the regulations should contact The Office of the Deputy Prime Minister, which is most helpful - or go to the following website (link below)

Richard Harrison, ETAP lighting

Source

Building Sustainable Design