The brightness and type of bulb determines the efficiency at which phosphorescent material charges. Efficient bulbs not only charge faster, but can obtain a brighter level of glow. For example, a black light shining on a glow surface for 30 seconds will cause that surface to be 10x brighter than a flashlight on it for 6 hours. Here is a simple list of bulbs in order from least to most efficient:
- White LED lights
- Blue/purple LED lights
- Incandescent standard light bulb
- Compact fluorescent or CFL light (spiral tube, screw-in)
- White LED's Blue/Purple LED's Incandescent
- Fluorescent bulb with long tubes
- UV LED lights
- Black light tube
- Direct sunlight
The efficiency of light as a phosphorescent charging source is determined by its brightness and its spectrum. White light is comprised of equal amounts of all of the colors, such as red, green, and blue. White light bulbs typically also emit ultraviolet (UV) light - the "color" above purple in the spectrum which humans can not see. Each part of the spectrum effects glow in the dark materials differently. Red light actually discharges the glow pigments. Green light is neutral. Blue Light inefficiently charges the pigments. Ultraviolet light charges the pigments efficiently. A standard incandescent light bulb emits similar amounts of the four colors above. The green does not effect the glow pigments. The red discharges and the blue charges in similar amounts, which results in a cancelation. The result is that only the ultraviolet is working to charge the phosphorescent pigments.
Therefore, when using a 100 watt incandescent light bulb as a charging source, only about 10-25 watts are working to actually charge the pigment. Therefore, a 60 watt black light bulb will far outperform the higher powered white light. The efficiency of white light can be determined by the ratios of the colors contained. "Warm" lights contain more red and therefore are poor for charging glow in the dark items. "Cool" or "Daylight" bulbs contain more blue and therefore are slightly more efficient. Fluorescent bulbs, both CFL and tube style, naturally emit more ultraviolet light, which makes them more efficient. Black lights have another major advantage. White light bulbs cause the human eye to adjust to the bright light. When the light is removed, it takes 15 minutes for human eyes to adjust back to the darkness. If your eyes are adjusted for a bright room, then even the brightest phosphorescent material will appear dim when the light is removed. Black lights do not cause your eyes to readjust. For most applications, this will cause the glow in the dark materials to "appear" considerably brighter.
The final major consideration is direct vs. reflected light. Many ceiling fixtures are designed to point light down onto a room. Therefore, the only light reaching the glow in the dark stars on your ceiling is reflected. Reflected light is extremely inefficient for charging. This holds true for sunlight entering through a window. While a room inside may look bright, it is mostly from reflected light. This is also why glow in the dark house numbers on a west-facing house are brighter at 10pm than an east-facing house.
A frequently asked question at Glow Inc. is "How long does it take to get a full charge?" The easy answer is that any of our products will be at their maximum charge from any light source in 20 minutes. However, that is a useless answer. "Maximum Charge" will change depending on the light source. A black light on for seconds can cause our products to glow brighter than an incandescent bulb lit for 10 hours. Of course, the speed of charge is also determined by the light source. A "full charge" is also a hard statement. Under black light, most pigments will get to 80% of their charge within seconds, 90% over 30 seconds, 95% over about 2 minutes, 100% in about 10 minutes. This is further complicated by the size of the pigment. Larger pigments can glow brighter and longer, but charge slower.
In conclusion, use a black light if possible. If white light is needed use CFL "Daylight" bulbs.