Halogen PAR lamps are the workhorses for retail product highlighting. Halogen bulbs are a type of incandescent but the presence of halogen gas in the inner capsule or "burner" enable the filament to burn hotter, generate more light and last longer that a standard incandescent. The ability of the "parabolic reflector" to get light out of the bulb and the lens' ability to concentrate the light on the target makes halogen a perfect source for accent lighting.
A typical retail store will use 75 or 90-watt lamps to provide product highlights. That means using a lot of electricity and generating a lot of heat. Halogen lamps are thought to be hotter than reflector incandescent lamps. The reality is a 75-watt light source of any type generates 75 watts of heat to be dealt with by the HVAC system. Halogens are thought to be hotter because the energy (heat and light) is concentrated by the lens. Halogen lamps put the same amount of heat into the space as incandescent, fluorescent or any other source of the same wattage. One watt of electricity equals a watt of heat.
The difference between halogen lamps which are a point source and compact fluorescent lamps which are a diffuse source is significant. Compact fluorescent reflectors should not be substituted for halogen accent lighting.
Advanced Energy Design Guide for Small Retail Buildings says this about compact fluorescents:
"Compact fluorescent lighting may be used for general store lighting but is less efficient than linear fluorescent and is much more expensive to dim. Compact fluorescent lighting should not be used for accent lighting."
Remembering that our objective for sustainable lighting is to meet the qualitative needs of the visual environment while minimizing the impact on the physical environment, we need to use a point source for accent lighting. If we decide the sales floor needs no accent lighting then we can use all fluorescent lighting. Office Depot made that determination. Walmart, Target, and Sears use accent lighting to draw your attention to products.
What ASHRAE says on this issue is, "To achieve the LPD recommendations in Chapter 3, halogen IR lamps may be used for accent lighting. Halogen IR lamps are defined, for the purpose of this Guide, as having a lamp efficacy of 20+ lumens per watt and using thin films to help redirect thermal energy through the filament, increasing light output.
Because of the infrared coating we can get more light with less energy. In the case of PAR38 halogen, we can nearly match the light output of a 90-watt with 60 watts -- 30% lower watts but with the same quality of light, if we use infrared coated halogens. Lower energy, longer life the payback basically means free light bulbs.
Ceramic metal halide lighting is different from the metal halide lighting you see in the warehouse and some retail stores like Home and Office Depot. They are efficient in terms of electricity in and light out but ceramic metal halide also has excellent color rendering.
Ceramic metal halide comes in 20, 39 and 70 watt sizes. The 39-watt metal halide has the light output of two 90-watt halogen bulbs. In some retail situations the number of heads can be reduced by half. In furniture stores the reduction is 20-30% for the number of track heads because room groups are displayed in a "U" configuration. Each CMH head saves $18.40 compared to the 90-watt halogen plus the reduction in heads.
Ceramic metal halide heads have an electronic ballast built into the fixture. There are self-ballasted CMH bulbs with the ballast in the bulb like compact fluorescents. You will see both types in retail especially grocery stores that now use CMH in produce, bakery, deli and meat departments.
With lamp life of 12,000 to 15,000 hours, CMH bulbs are twice as expensive as halogen bulbs but there are fewer bulbs to buy and service and electricity savings are significant. Rates of 15-16 cents per kilowatt hour should take a look at ceramic metal halide lighting for product accent lighting.