I wonder if the lamp is fading due to age and needs to be replaced. Do you have the 6X6 light mixing box or the 35mm? If you have the 35mm it will be darker and will not cover 6X6. Although a long shot has anyone added an addtional layer of material for diffusion? My color head come to full intensity almost immediately and is in the same ball park as the condenser head in in terms of brightness with the 6X6 box and condenser set.