I've noticed some CFLs need a few minutes to warm up, or reach full brightness. Is there a way to determine which warm up fastest?

By choosing an ENERGY STAR qualified CFL, you are assured that it will turn on in less than a second, and reach at least 80% of full light output within 3 minutes. If the CFL doesn't have the ENERGY STAR, both start time and warm up time could be much longer. Additionally, many lighting manufacturers offer "instant on" CFLs. Some spiral and mini-spiral products incorporate "instant-on" technology in their products and display this feature prominently on the product packaging. Some covered or reflector CFLs actually do take longer to warm-up, but the tradeoff is that they last longer than regular CFLs. ENERGY STAR qualified CFL products that are covered (like incandescent shaped, reflectors, globes, candles) have a higher operating temperature so they require a compound called amalgam to perform properly. This compound actually increases the bulb life and the light output! The one tradeoff is that these CFLs cannot offer "instant full brightness." The CFL will turn on, but may take up to three minutes to warm-up to reach full light output.