All Keeler instruments use genuine Halogen and Xenon technology, yielding a brighter, whiter illumination and a longer life. Look at the bottom of your bulb to identify if your instrument is Blue 2.8V (Dry cell battery) or Red 3.6V (Rechargeable battery). The Standard/Practitioner ophthalmoscope Bulb is a 2.8v replacement bulb for the Keeler Standard and Practitioner ophthalmoscope. These bulbs are supplied in packs of two.